Hindawi Publishing CorporationInternational Journal of PhotoenergyVolume 2013 Article ID 268723 13 pageshttpdxdoiorg1011552013268723
Research ArticleThe Synergistic Effect of Nitrogen Dopant and CalcinationTemperature on the Visible-Light-Induced Photoactivity ofN-Doped TiO2
Yao-Tung Lin1 Chih-Huang Weng2 Hui-Jan Hsu1 Yu-Hao Lin1 and Ching-Chang Shiesh3
1 Department of Soil and Environmental Sciences and Center of Nanoscience and NanotechnologyNational Chung Hsing University TaiChung 402 Taiwan
2Department of Civil and Ecological Engineering I-Shou University Kaohsiung 84001 Taiwan3Department of Horticulture National Chung Hsing University TaiChung 402 Taiwan
Correspondence should be addressed to Yao-Tung Lin yaotungnchuedutw
Received 9 January 2013 Revised 28 March 2013 Accepted 29 March 2013
Academic Editor Jiaguo Yu
Copyright copy 2013 Yao-Tung Lin et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
The synergistic effect of nitrogen content and calcinations temperature on the N-doped TiO2catalysts prepared by sol-gel method
was investigated The phase and structure chemical state optical properties and surface areapore distribution of N-doped TiO2
were characterized using X-ray diffraction spectrometer high-resolution transmission electron microscope X-ray photoelectronspectroscopy UV-vis diffusion reflectance spectroscopy and Brunauer-Emmett-Teller specific surface area Finding showed thatthe photocatalytic activity ofN-dopedTiO
2was greatly enhanced compared to pure TiO
2under visible irradiation N dopants could
retard the transformation from anatase to rutile phase Namely N-doping effect is attributed to the anatase phase stabilizationTheresults showed nitrogen atoms were incorporated into the interstitial positions of the TiO
2lattice Ethylene was used to evaluate
the photocatalytic activity of samples under visible-light illumination The results suggested good anatase crystallization smallerparticle size and larger surface are beneficial for photocatalytic activity of N-doped TiO
2TheN-doped TiO
2catalyst prepared with
ammonia to titanium isopropoxide molar ratio of 20 and calcinated at 400∘C showed the best photocatalytic ability
1 Introduction
Titanium dioxide (TiO2) is an effective photocatalyst due to
its inexpensiveness chemical stability nontoxicity biologi-cal and chemical inertness and long-term stability againstphoto-corrosion and chemical corrosion [1 2] In the lasttwo decades many works have been done on expandingand augmenting the utility of TiO
2in heterogeneous pho-
tocatalysis (eg water purification air cleaning and watersplitting for the production of hydrogen) [2ndash5] self-cleaningsurfaces [6] inactivation of bacteria and fungi [7 8] solarcells [9] anticorrosive coatings [10] and Li-ion batteries [11]TiO2has three phases in nature brookite (orthorhombic)
anatase (tetragonal) and rutile (tetragonal) It is amorphousat temperature up to 300∘C becoming anatase and rutiletypically at 350 and 800∘C respectively [3] Anatase powderwith good crystallinity small grain size and high specific
surface area is desirable as long as the photocatalytic activityis concerned However its wide band gap of 32 and 30 eVfor anatase and rutile polymorphs respectively requires UVlight for the excitation of electron-hole pairs It only uses 4-5 of the UV light in the solar irradiation To utilize solarenergy effectively many attempts have been made to modifythe properties of TiO
2 such as doping with transition metal
ions [12ndash14] or nonmetal anions [3 15ndash23] and sensitizationwith organic dyes [24 25] Among the nonmetal-dopingTiO2photocatalysts the simplest and most feasible TiO
2
modification approaches for achieving visible-light-drivenphotocatalysis seem to be N-doping that is doping nitrogenatoms into interstitial (or substitutional) sites in the crystalstructure of TiO
2 Sato [4] was the first to report on nitrogen-
doped TiO2 It was treated with various nitrogen sources
such as urea ammonia ammonium chloride and nitricacid Asahi et al have prepared TiO
2minus119909N119909films whose
2 International Journal of Photoenergy
absorption activity not only was shifted toward the longervisible wavelength but also had higher thermal stability andless recombination centers of charge carries than the metal-doped TiO
2[5] However to date little research has been
conducted on gaining in-depth information on the propertiesof the interstitial (or substitutional) N-doped TiO
2 as well as
its photocatalytic activity Different dopants result in TiO2of
different properties and consequently alter the photocatalyticactivity of the materials Currently few works have focusedon the synergistic effects of nitrogen dopant and calcinationtemperature on the characteristics and visible-light-inducedphotoactivity of N-doped TiO
2[6]
In this study we focused on sol-gel synthesis process forthe preparation of nitrogen-doped TiO
2catalysts (N-TiO
2)
because the wet processes have the advantages of low costease of scale-up and stablility for practical applications Theeffects of N atom and calcination temperature on the struc-tural optical and photocatalytic properties of N-TiO
2were
assessedThe gel samples were calcined at 400 500 600 700and 800∘C The photocatalysts were characterized using X-ray diffraction (XRD) high-resolution transmission electronmicroscope (HRTEM) X-ray photoelectron spectroscopy(XPS) UV-vis diffusion reflectance spectroscopy (UV-visDRS) Brunauer-Emmett-Teller (BET) specific surface area(119878BET) and thermogravimetric-differential thermal analysis(TG-DTA) The transition from amorphous to anatase andrutile phases at different calcination temperatures was alsoexplored Ethylene was chosen as a probe reactant becauseit is structurally simple has relatively high reactivity and isthe parent compound of many widespread volatile organiccompounds (VOCs) of environmental concern (eg TCE andtetrachloroethylene) The object of this study is to investigatethe synergistic effects of nitrogen content and calcinationtemperatures in the synthesis process of N-doped TiO
2
prepared by sol-gel process and to investigate the influenceof ethylene on photocatalytic decomposition
2 Materials and Methods
21 Preparation of N-Doped TiO2Catalyst Titanium iso-
propoxide (TTIP C12H28O4Ti 97 Aldrich) a highly re-
active alkoxide was used as precursor Aqua ammonia(NH4OH) was used as nitrogen source A given amount of
aqua ammonia was added to the distilled water while beingstirred until it completely dissolved at room temperatureThen the solution was added dropwise to a constant amountof titanium isopropoxide as to obtain an aqua ammoniato TTIP molar ratio (AT) of 1 1 the TiO
2sample was
designated as N-TO2 While the mixture was being stirred
vigorously the urea solution was introduced to the TTIPHydrolysis and ploycondensation reactions occurred Thereactant was stirred continuously for one hour after all aquaammonia solution was dissipated The sol was aged in air for24 hr to allow further hydrolysis The final sol was left on thebench top to allow thickening After aging the sol was driedat 70∘C for 24 hr to evaporate the solventThe residual xerogelwas crushed to fine powder before calcined in a furnace at400 500 600 700 and 800∘C respectively for 3 hr Pure
TiO2powder was also prepared without the presence of aqua
ammonia following the same procedures as described aboveThe nitrogen-doped samples were labeled AxTy where 119909and 119910 refer to the aqua ammonia to TTIP molar ratio (AT)and calcining temperature respectively For example A20T4means the N-TiO
2prepared with AT molar ratio 20 and
calcinated at 400∘C
22 Characterization The 119878BET of the samples was deter-mined using nitrogen adsorption method measured with aMicromeritics ASAP 2020 adsorption apparatus Pore sizeand pore volume were calculated by the BJH isotherm Thecrystallization behavior and stability of N atoms in N-TiO
2
were monitored using a TG-DTA (STA 6000 PerkinElmer)while the sample was being heated from room temperatureto 1000∘C at 10∘CminThe morphology structure and grainsize of the samples were characterized by a high-resolutiontransparent electromicroscopy (HRTEM JEM-2010 JEOL)To study the optical response of N-TiO
2samples (120582 = 200ndash
800 nm) UV-vis DRS (U3900H Hitachi) were recordedusing a spectrophotometer with an integrating sphere attach-ment and Al
2O3was used as the reference The chemical
environment information and the N concentration of all ofthe samples were measured by X-ray photoelectron spectra(XPS) (PHI 5000 VersaProbeScanning ESCA Microprobewith aC
60ion gun) All sampleswere collected in vacuumand
transferred to the main ultrahigh-vacuum (UHV) chamberfor measurements The shift of binding energy due to relativesurface charging was corrected to the C 1s level at 285 eV asan internal standard The XPS peaks were assumed to haveGaussian line shapes and were resolved into components by anonlinear least-squares procedure after proper subtraction ofthe baseline The crystallinity and phase of the samples wereanalyzed byXRD (PANalytical XrsquoPert-ProMPDPW304060)with Cu-Ka radiation at a scan rate of 005∘ 1s in the rangefrom 20 to 80∘
23 Photooxidation Performance The experiment setup andoperating conditions for photocatalytic activity tests werethe same as those reported previously [7] The catalyst wasprepared by depositing suspension of the as-prepared catalystat the bottom surface of the reactor that was subsequentlydried at ambient conditionThe obtained catalyst film densityon the bottom surface of reactor was kept at 4mgcm2 Theexperiment setup and operating conditions for photocat-alytic activity tests were the same as those in our previousreports [7] The photocatalytic activity experiments of theas-prepared catalysts for the oxidation of ethylene in gasphase were performed at room temperature using a 250mLphotocatalytic reactor Air with 60 relative humidity waspassed through the reactor with the sample inside for 1 hrto reach equilibrium and then a desired amount of ethylenewas injected into the reactor with a gastight syringe Theethylene inside the reactor was taken at regular intervals withgas-tight syringe and analyzed using gas chromatographs(PerkinElmer Clarus 500 USA) equipped with a flameionization detector (FID) and a thermal conductivity detector(TCD) detection The GC instrument was equipped with an
International Journal of Photoenergy 3
Elite-Plot-Q capillary column (Agilent Technologies) Theethylene was allowed to reach adsorption equilibrium withthe catalyst in the reactor prior to irradiation Two 500-W horizontal halogen lamps (95 cm in length PHILIPS)were used to simulate the solar light The lamp equippedwith a cut-off filter (120582 gt 400 nm) was vertically placedoutside the photocatalytic reactor Light intensity at thecatalyst surface was 16mWcm2 Blank experiments usingan uncoated (no catalyst) glass plate had no effect on theethylene concentration and did not generate any carbonmonoxide or carbon dioxide (see supplementary materialonline at httpdxdoiorg1011552013268723) The photo-catalytic activity of the catalyst can be quantitatively evaluatedby comparing the apparent reaction rate constants
3 Results and Discussion
31 Thermal Analysis To investigate the process of phasetransformation of titanium(IV)-oxide-hydroxide to titaniumoxide and the effect of nitrogen doping content on thetransformation from anatase to rutile thermoanalytic tech-niques including TGA and DTA were conducted Typicallythe hydrothermal weight loss is attributed to a multistepof polycondensation of titanium(IV)-oxide-hydroxide andphase transformation of anatase into rutile or brookite fromroom temperature to 700ndash800∘C as shown in Figure 1 andTable 1 DTA measurements established the transformationof TiO
119909(OH)119910into TiO
2including two endothermic and
one exothermic peaks from room temperature to 398∘C(Figure 1) A sharp endothermic peaks at 105∘C due to therelease of absorbed water while the other minor peak at253∘C is referred to as the desorption of organic Therewas a corresponding weight loss from TGA of about 198and 94wt respectively In the region mentioned abovethe finely exothermic peak around 276∘C is ascribed to thethermal decomposition of unhydrolyzed TTIP with about08 wt weight loss The weak thermal effect at 276ndash730∘Cis accompanied by obvious exothermic peak at 451∘C whichcan be assigned to the crystallization of the amorphous phaseto anatase At around 730∘C an obvious exothermic peakwas observed owing to the oxidation of carbon residue andevaporation of chemisorbed water which can be assignedto the phase transformation from anatase titania to rutileTiO2 It can be concluded from the DTA result that the as-
prepared TiO2sample was amorphous According to TGA
the weight loss roughly consists of three distinct stages Thefirst stage was up to 276∘C over which the mass loss is thegreatest A mass loss of up to 30 was observed which isattributed to the evaporation of the physical adsorbed waterand the release of organic The second stage is from 276 to451∘C where the mass loss is about 17This corresponds tothe thermal decomposition of unhydrolyzed TTIP The thirdstage is from 451 to 730∘C and the mass loss is about 07which is attributed to the removal of chemisorbed water Atabout 730∘C no mass loss was observed The exothermicpeaks of N-TiO
2prepared at 05 10 and 20 AT ratios
were at 710 720 and 730∘C respectively (Table 1)The resultsindicated that nitrogen atoms doped in TiO
2could prevent
100
80
60
40
20
0
60
50
40
30
20
10
00 100 200 300 400 500 600 700 800
Wei
ght l
oss (
)
Hea
t flow
(mW
mg)
Temperature (∘C)
198 94 17 07
105∘ C
253∘ C
276∘ C
451∘ C
730
∘ C
Anatase into rutile
Release of adsorbed water
Desorption of organics
Amorphous into anatase
Thermal decomposition of unhydrolyzed TTIP
Figure 1 TG-DTA curve of N-TiO2samples prepared with 20
ammoniaTTIP ratio
phase transition of anatase to rutile because as far as pureTiO2was concerned most TiO
2particles were transformed
into rutile at 700∘C
32 Phase and Structure The characteristics of N-TiO2at
various calcination temperatures and molar ratios of ATare summarized in Table 1 Figure 2 shows the XRD patternof the N-TiO
2samples at various AT ratios and annealed
at different temperatures The presence of peaks (2120579 =2544∘ 3806
∘ and 4824∘) was regarded as an attributive
indicator of anatase titania and the presence of peaks (2120579 =2754∘ 3614
∘ and 4120∘) was regarded as an attributive
indicator of rutile titaniaThediffraction peaks for the anatase(JCPDSno 21-1272) and rutile (JCPDSno 21-1276) phases aremarked with ldquoArdquo and ldquoRrdquo respectively and the correspondingdiffraction planes are given in parenthesis No N-derivedpeaks were detected in all the patternsThismay be caused bythe lower concentration of the doped species and the limiteddopants may have moved into either the interstitial positionsor the substitutional sites of the TiO
2crystal structure which
is consistent with [8 9] The average grain size was estimatedat 28ndash131 nm comparable to that from the HRTEM imageA comparison of XRD patterns clearly shows that nitrogendoping significantly changes the crystalline size and thecrystal structure of TiO
2
The transformation from the amorphous to the crys-talline form of TiO
2usually requires temperatures close
to 300∘C [8] For the samples prepared with 20 AT andcalcinated at 400ndash500∘C (Figure 2(a)) the intensities ofthe anatase peak are increased and the width of the (101)plane diffraction peak becomes narrower as the calcinationtemperature increases implying an improvement and growthin crystallinity Increasing the temperature to 800∘C theintensity of anatase peak decreases but the rutile peaksappear suggesting the transformation of anatase to rutilephase The average crystalline size was 32 85 and 103 nmand the mass percentage of anatase was 90 60 and 6 forsamples prepared at 20 AT and calcination temperature
4 International Journal of Photoenergy
Table 1 Characteristics for N-TiO2 at various ammoniaTTIP molar ratios under different calcination temperatures
SampleaXRD BET TG-DTA TEM Optical properties
Phase ratio Crystallite size Surface area (m2g) Abrarr Rc Temp (∘C) Size (nm) 1205821198921 1198641198921 1205821198922 1198641198922
Ab Rc Ab (nm) Rc (nm) (nm) (nm) (nm) (nm)A00T4 90 10 32 mdash 93 703 11 plusmn 1 392 316 mdash mdashA05T4 89 11 28 mdash 108 710 12 plusmn 1 392 316 505 246A10T4 90 10 28 mdash 119 720 12 plusmn 1 391 317 506 245A15T4 87 13 29 mdash 119 728 11 plusmn 1 388 320 513 242A20T4 90 10 32 mdash 98 730 12 plusmn 1 390 318 510 243A25T4 90 10 37 mdash 98 728 12 plusmn 1 392 316 515 241A30T4 92 8 37 mdash 86 729 12 plusmn 1 392 316 514 241A00T5 94 6 46 mdash 50 703 13 plusmn 2 402 308 mdash mdashA05T5 89 11 46 98 64 710 13 plusmn 1 404 307 503 247A10T5 90 10 41 87 68 720 15 plusmn 2 400 310 508 244A15T5 91 9 40 mdash 71 728 15 plusmn 2 396 313 517 240A20T5 94 6 45 mdash 62 730 15 plusmn 2 394 315 513 242A25T5 94 6 49 mdash 55 728 17 plusmn 2 397 312 507 245A30T5 94 6 47 mdash 53 729 17 plusmn 2 397 312 510 243A00T6 34 66 106 156 7 703 24 plusmn 2 420 295 mdash mdashA05T6 14 86 86 128 8 710 40 plusmn 3 422 294 mdash mdashA10T6 14 86 81 132 9 720 40 plusmn 4 425 292 mdash mdashA15T6 22 78 79 141 14 728 35 plusmn 3 424 292 mdash mdashA20T6 60 40 85 184 17 730 34 plusmn 3 415 299 mdash mdashA25T6 78 22 90 184 16 728 35 plusmn 4 416 298 mdash mdashA30T6 74 26 97 169 12 729 36 plusmn 4 415 299 mdash mdashA00T7 6 94 131 177 2 703 80 plusmn 5 424 292 mdash mdashA05T7 3 97 95 148 5 710 145 plusmn 10 428 290 mdash mdashA10T7 3 97 102 149 6 720 145 plusmn 10 429 289 mdash mdashA15T7 3 97 92 159 6 728 150 plusmn 11 428 290 mdash mdashA20T7 6 94 103 163 4 730 170 plusmn 13 428 290 mdash mdashA25T7 15 85 108 178 8 728 60 plusmn 6 426 291 mdash mdashA30T7 15 85 117 182 6 729 60 plusmn 6 427 290 mdash mdashA00T8 1 99 mdash 174 3 703 200 plusmn 17 424 292 mdash mdashA05T8 1 99 mdash 161 3 710 190 plusmn 15 428 290 mdash mdashA10T8 1 99 mdash 159 3 720 160 plusmn 13 429 289 mdash mdashA15T8 1 99 mdash 171 3 728 170 plusmn 15 428 290 mdash mdashA20T8 1 99 mdash 164 2 730 160 plusmn 14 428 290 mdash mdashA25T8 3 97 106 184 4 728 200 plusmn 18 427 290 mdash mdashA30T8 3 97 127 179 3 729 170 plusmn 15 429 289 mdash mdashaAXXTY ammoniaTTIP molar ratio = 0XX calcination temperature = Y00∘CbAnatasecRutile
of 400 600 and 700∘C respectively The maximum meansize of anatase and rutile crystallites was observed at 800∘CResults agreed with those reported that the crystalline sizegrows and the content of anatase diminishes as calcinationtemperature increases [8 10ndash13] For the samples prepared at05 AT the anatase peaks appear at temperatures 400 and500∘C Increasing the temperature to 500∘C the intensity ofanatase peak decreases but the rutile peaks appear Whentemperature is increased further to 600∘C rutile becomesa main phase In this case the anatase-to-rutile phasetransformation temperature is between 400 and 500∘C XRD
patterns of samples prepared at 30 AT and annealed at700∘C show both anatase and a rutile phase indicating thatanatase-to-rutile phase transformation is shifted to highertemperature It can be seen that the presence of nitrogencan restrain the formation and growth of TiO
2crystal phase
thereby retarding the anatase-to-rutile phase transformationThis result is further supported by the appearance of rutilein XRD patterns of sample prepared at 05 and 15 GTat 600∘C and disappearance for samples prepared at GTgreater than 20 at 600∘C (data not shown) Comparedwith P25 the peak position of the (101) plane of N-doped
International Journal of Photoenergy 5
A A A
A A
AR
R
RR R R
(101) (110) (004) (204)(200)
(105)(211)
(101)
(111)
(210) (211) (220)
Inte
nsity
(au
)
20 30 40 50 60 70 80
Calcination temperature (∘C)400
500
600
700
800
2120579 (deg)
AT ratio 2
(a)
A A A A A A(101) (004) (204)(200)(105)(211)
Inte
nsity
(au
)
20 30 40 50 60 70 80
0051
15
2253
2120579 (deg)
AT ratio
Calcination temperature 400∘C
P25
(b)
Figure 2 XRD patterns of N-TiO2samples prepared (a) at various calcination temperatures and (b) with various ammoniaTTIP ratios
TiO2shifted slightly to higher 2120579 value and the peak was
broader as NT ratio increases suggesting distortion of thecrystal lattice of TiO
2by the incorporation of nitrogen The
crystalline sizes of samples calcinated at 400∘C and pre-pared at 05 15 20 and 30 AT were 28 29 32 and37 nm respectively The average crystalline size of samplesincreases with increase in AT revealing that nitrogen canenhance the growth of N-TiO
2crystals Results agreed with
those reported that the crystalline size grows as nitrogento Ti proportion increases [14] The results reveal that thephase transformation temperature of anatase to rutile wasprogressively increased when the amount of N dopant wasincreased Clearly calcination temperature andAT ratio playa significant role in the formed crystal structure and particlesize (Figure 3)Higher temperature favors the growth of rutilestructure and produces N-TiO
2nanoparticles with larger
particle size Thus a fine control of calcination temperatureand AT ratio is crucial for obtaining a pure phase of N-TiO
2
Further insights into the effect of calcination and dopingon the morphology and structure of the N-TiO
2samples can
be obtained from HRTEM image (Figure 4) The selectedarea electron diffraction pattern and TEM confirmed itshighly crystalline anatase or rutile structure The observedd-spacing from HRTEM image is 3522 A and is comparableto 352 A previously reported for (101) crystallographic planeof undoped anatase [15ndash18] The HRTEM image showedthe nanocrystallines with primary grain size around 11ndash200 nm From the TEM images the particles in N-TiO
2
samples are monodispersed The crystalline form aggregateswith a mesoporous structure The formation of mesoporousstructure is similar to that reported in the literature [1920] First monodispersed amorphous titanium oxide solparticles are formed by the hydrolysis processes Then themonodispersed sol particles are crystallized and aggregatedunder calcination treatment to form mesoporous crystallineBased on the HRTEM results the calcination temperature
100
80
60
40
20
0400 500 600 700 800Calcination temperature (∘C)
AmmoniaTTIP molar ratio
Ana
tase
()
005115
2253
Figure 3 The anatase content of N-TiO2samples as a function of
the various ammoniaTTIP molar ratios
significantly changes the size of particles (Table 1) The grainsize of crystalline is in consistent with the calculated valueobtained from XRD patterns (Table 1) The grain size ofsamples increases with the calcination temperatureMorpho-logical observation by TEM and XRD calculations revealsthat the large particle size of A20T8 was mainly caused byagglomeration and the growth of crystallite size
33 Surface Area and Pore Size Distribution Typical nitrogenadsorption-desorption isotherms of N-TiO
2photocatalyst
6 International Journal of Photoenergy
400∘C
10nm
(a)
500∘C
10nm
(b)
600∘C
50nm
(c)
700∘C
50nm
(d)
100nm
800∘C
(e) (f)
Figure 4 TEM images of N-TiO2prepared (a)ndash(e) at various calcination temperatures with 20 ammoniaTTIP ratio and (f) the selected
area electron diffraction of A20T4
are shown in Figure 5 The 119878BET of N-TiO2prepared with 20
AT ratio at calcined 400 500 600 700 and 800∘C was 9862 17 4 and 2m2g respectively Obviously the values of119878BET and pore volume of N-TiO
2prepared with the same AT
ratio decreased with increasing calcination temperaturesSuch phenomenon could be attributed to the collapse of themesoporous structure the growth of TiO
2crystallites and
the removal process of nitrogen core by high-temperaturecalcination Consequently N-TiO
2calcined at 800∘C has the
least 119878BET Based on the results obtained the hysteresis loop ofN-TiO
2is significantly shifted in direction of higher relative
pressures as calcination temperature increases indicatingmuch larger mesorpore The average pore size of N-TiO
2
increased with increasing calcination temperature due to theformation of slit-like pores [21]
The N-TiO2samples obtained at various calcination
temperatures gave different nitrogen adsorption isotherms(Figure 5) implying differences in their porous structureThe N-TiO
2samples prepared at low calcination temperature
(ie 400 and 500∘C) exhibited a type IV isotherm and atype H2 hysteresis loop at lower relative pressure regionwhich are typical characteristics of mesoporous structurewith ink bottle pores Note that the adsorption branches ofthese isotherms resembled type II indicating the presence ofsome macropores Otherwise the N-TiO
2samples prepared
at higher calcination temperature (ie 600ndash800∘C) exhibiteda type V isotherm and a type H3 hysteresis loop at higherrelative pressureThe hysteresis loop at lower relative pressureregion (04 lt 119875119875
0lt 08) was attributed to a smaller mes-
opore while that at the higher relative pressure (08 lt1198751198750lt 10) was of larger mesopores Thus samples prepared
at high calcination temperature (gt600∘C) had a wide poresize distribution in the mesopores scale The isotherm of N-TiO2prepared at higher calcination temperature was below
that of lower calcination temperature (Figure 5) indicatinglower surface area and pore volume of the former Furtherobservation from Table 1 indicated that 119878BET for the N-TiO
2
samples at the same AT ratio increased with increasingcalcination temperature (Figure 5(c)) Results reveal thatall N-TiO
2samples calcined at various temperatures show
monomodal pore size distributions and mesopores may beassigned to the pores among interaggregated particles (datanot shown) With calcination temperature increasing thereis a significant tendency of pore size distribution toward tothe bigger pore size The increase of pore size is due to thecorruption of smaller pores during calcination as the smallerpores endured much greater stress than the bigger poresFormation of bigger crystalline aggregation upon increasein temperature could form bigger pores also Consequentlythe pore size increases while the pore volume decreases with
International Journal of Photoenergy 7
200
150
100
50
00 02 04 06 08 1
400500600
700800
IV
IV
V
VV
AmmoniaTTIP ratio 2Calcination temperature (∘C)
Qua
ntity
adso
rbed
(cm
3g
STP
)
Relative pressure (1198751198750)
(a)
0 02 04 06 08 1
005115
2253
IV
250
200
150
100
50
0
H3
Calcination temperature 400∘CAmmoniaTTIP ratio
Qua
ntity
adso
rbed
(cm
3g
STP
)
Relative pressure (1198751198750)
(b)
0
120
100
80
60
40
20
0400 500 600 700 800
Calcination temperature (∘C)
Surfa
ce ar
ea (m
2g
)
05115
2253
AmmoniaTTIP ratio
(c)
Figure 5 Nitrogen adsorption and desorption isotherms of N-TiO2samples (a) calcined at various temperatures (b) prepared with various
ammoniaTTIP molar ratios the surface area as a function of calcination temperature
calcinations temperature increasing Based on the TEM andBET results the mesopores of TiO
2were decreased due
to the heat shrinkage of calcination The results indicatedthat calcination at high temperature and in the presence ofnitrogen atoms will help to improve the thermal stabilityof the photocatalyst While the calcination temperature wasincreased both the specific surface area and the pore vol-ume of N-TiO
2samples decreased This indicated that the
average pore size increased while the pore volume and the
specific surface area decreased with calcination temperatureincreasing
34 Optical Properties The typical UV-vis diffuse reflectancespectra of N-TiO
2are shown in Figures 6(a) and 6(b) It can
be seen that nondoped TiO2(P25) has only one light sharp
edge (120582 = 410 nm) which can be assigned to the band gapof TiO
2 while part of N-TiO
2showed two absorption edges
and a noticeable shift to the visible light region as compared
8 International Journal of Photoenergy
400500600
700800
2
15
1
05
0
Abso
rban
ce (a
u)
Abso
rban
ce (a
u)
200 300 400 500 600 700 800Wavelength (nm)
Wavelength (nm)Calcination temp (∘C)
05
04
03
02
01
0350 400 450 500 550
NTi 2 molar ratiocalcination at different temperatures
AT ratio 2
A20T4A20T5A20T6A20T7A20T8
P25
(a)
2
15
1
05
0
Abso
rban
ce (a
u)
200 300 400 500 600 700 800Wavelength (nm)
Abso
rban
ce (a
u)
Wavelength (nm)
04
04
03
03
02
02
01
01380 400 420 440 460 480 500 520 540
Calcination at 400∘C temperaturedifferent NTi molar ratios
325
215
1050P25
A00T4A05T4A10T4A15T4
A20T4A25T4A30T4
AT ratio
Calcination temperature 400∘C
(b)
Figure 6 The typical UV-vis DR spectra of N-TiO2samples (a) prepared with 20 ammoniaTTIP molar ratio and calcined at various
temperatures (b) prepared with various ammoniaTTIP molar ratios and calcined at 400∘C
to that of the TiO2(ie P25) This phenomenon should be
ascribed to either the nitrogen doping andor sensitizationby a surface-anchored group The calcination temperatureand AT ratio are the crucial factor that can further affectthe absorption as seen in Figure 6 Similar phenomenonhad been reported by previous publications [17 22ndash25] Theabsorption edges of the N-TiO
2samples show continuous
red shift as the calcination temperature changes from 400to 700∘C which can be assigned to the intrinsic band gapabsorption of TiO
2 The shift is too minor to be observed
when the calcination temperature changes from500 to 600∘Cwhich is possibly caused by the synergetic effect of the loss ofthe nitrogen and the increase of the TiO
2crystallinity during
the calcination processThe absorption threshold (120582119892) can be
determined using the onset of the absorption edges by thesection of the fitting lines on the upward and outward sectionof the spectrum (shown in the graph inserted in Figure 6)[23] Table 1 lists the determined 120582
119892(nm) and the derived
band gap energy values The band gap of N-TiO2(119864119892) was
calculated using the 119864119892= 1240120582
119892equation It also can be
seen that N-TiO2samples have two characteristic light
absorption edges One of them corresponds to the band gapof TiO
2(1205821198921= 390sim430 nm) while the other originates from
the N-induced midgap level (1205821198922= 505sim517 nm) The color
of the samples was different with calcination temperatureand AT ratio The color of N-TiO
2samples prepared with
20 AT ratio and calcinated at 400 600 and 700∘C wasvivid yellow yellow and white respectively There is no 120582
1198922
when N-TiO2calcinated above 600∘C It can be ascribed to
the amount of N dopant decreased The color of N-TiO2
prepared with 00 10 20 and 30 AT ratio and calcinatedat 400∘C was white pale yellow yellow and vivid yellow
respectively The phenomenon that the AT ratio increasesthe shifting of the spectra towards visible region was clearlyobserved (Figure 6(a)) The absorption threshold (120582
119892) was
increased with increasing AT ratio It reveals that morenitrogen doping in the matrix of TiO
2structure results in a
shift of absorbance region toward visible light wavelengthThis is possible attribute to the nitrogen incorporated intoTiO2lattice and formation of new electronic state above
valence band caused by nitrogen doping to generate a redshift
35 Analysis of Chemical State The chemical states of dopingimpurity are critical to the optical property band gap andphotocatalytic activity of nitrogen-dopedTiO
2 To investigate
the chemical states of the doping nitrogen XPS spectra wereapplied to examine three regions the Ti 2p core level near460 eV the O 1s core level near 530 eV and the N 1s core levelnear 400 eV Figure 7 shows the experimental observation ofsurface chemical composition and the electronic structuresof N-TiO
2samples using XPS XPS peaks showed that the N-
TiO2contained only Ti O N elements and a small quantity of
carbon The presence of carbon was ascribed to the residualcarbon from the precursor solution and the adventitioushydrocarbon from the XPS instrument itself In Figures 7(a)and 7(b) the binding energy (BE) peaks corresponding toN 1s core levels for N-TiO
2are observed one major peak at
400 eV The N 1s peak at 400 eV is ascribed to the presenceof the oxidized nitrogen species and the nitrogen may beincorporating into the interstitial positions of the TiO
2lattice
and to form a TindashOndashN structure [26 27] No other N 1s peakswere detected in N-TiO
2samples As shown in Figure 7 N 1s
peak at 400 eV slightly decreased with increasing calcination
International Journal of Photoenergy 9
Bind energy (eV)
Inte
nsity
(au
)800
700
600
500
400
Calcination temp (∘C)Ti-O-N
390 395 400 405 410
AT ratio 2
(a)
Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
325
2
15
1
05
0
Ti-O-N
390 395 400 405 410
AT ratio
(b)
Bind energy (eV)
Inte
nsity
(au
) 800
700
600
500
400
Calcination temp (∘C)
Ti-O
524 526 528 530 532 534 536
AT ratio 2
(c)
Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
3
25
2
15
1
05
0
Ti-O
524 526 528 530 532 534 536
AT ratio
(d)
454 456 458 460 462 464 466 468Bind energy (eV)
Inte
nsity
(au
)
4582
4581
4583
458
4583
800
700
600
500
400
Calcination temp (∘C)AT ratio 2Ti4+2p32
Ti4+2p12
(e)
454 456 458 460 462 464 466 468Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
3
25
2
15
1
05
0
Ti4+2p32
Ti4+2p12 AT ratio
(f)
Figure 7 XPS survey and core level spectra of (a)-(b) N 1s (c)-(d) Ti 2p and (e)-(f) O 1s of N-TiO2samples
temperature This is different from the N-TiO2prepared by
flame oxidation in which nitrogen partially substitutes theoxygen sites in the TiO
2[28] The preparation method plays
an important role in determining the nitrogen state in TiO2
band structure [26 29 30]Depending on the nitrogen source
and experimental conditions N species are incorporated intoTiO2in interstitial form or substitutional form [31 32] The
interstitial N-doping is favored when the doping is carriedout under oxygen-rich conditions and the substation-typeN-doping occurs under reducing conditions [31ndash33] Therefore
10 International Journal of Photoenergy
from the atomicN 1sXPS spectra the interstitial sites (400 eV)were observed under air atmosphere
The XPS spectra of Ti 2p regions are shown in Figures7(c) and 7(d) The peaks at around 4585 and 4642 eV forP25 are ascribed to Ti 2p
32and Ti 2p
12of TiO
2(data not
shown)The line separation between Ti 2p12
and Ti 2p32
was57 eV which is consistent with the standard binding energyAccording to Figure 7 all spectra of Ti 2p
12are symmetry
The spectra of Ti 2p12
are consistent of single state and thebanding energy of peaks is 4580ndash4583 eV which shows aredshift of 05 eV compared to the binding energy of Ti4+in P25 This suggests that Ti3+ was present in N-TiO
2and
the distance of peaks between Ti 2p12
and Ti 2p32
is 57ndash59 eV The 396 eV peak is assigned to the atomic b-N stateand generally proves the presence of TiAN bonds formedwhen N atoms replace the oxygen in the TiO
2crystal lattice
[30]The peak characteristic for TindashN (396 eV) is not presentindicating the absence of the TiN phase in the N-TiO
2
samples [34]The results show that the binding energies of Ti2p peaks shift to lower energieswith a negative shift ofsim05 eVfor the N-TiO
2due to the N doping [27] The lower binding
energy than a typical Ti 2p signal of Ti4+ oxidation state sug-gests that titanium cation has a considerable interaction withthe doped nitrogen and thus TiO
2lattice is modified [27
35] Nitrogen doping accompanies the formation of oxygenvacancies andor Ti3+ defects resulting in slight shifts of theTi 2p peak toward the lower binding energy [36ndash38] Hencethe red shifts of the Ti 2p peak in comparison with P25 areused to highlight the successful nitrogen doping into the TiO
2
lattice The XRD results did not indicate the formation ofTiN bondsTherefore results indicate that the titanium atombonds with oxygen but not nitrogen Thus a shift towardlower binding energy of Ti 2p and the binding energy of N1s upon nitrogen addition indicate that the nitrogen can beindeed incorporated into the interstitial positions of TiO
2
lattice and the formation of TindashOndashN bonding by partiallyinterstitial with a carbon atom
The incorporation of nitrogen into the oxide latticeshould influence the BE of O 1s as wellTheXPS spectra of theO 1s core level consists of the one peak (Figures 3(e) and 3(f))at around 5293ndash5295 eV which is ascribed to TindashO bondin the TiO
2lattice [30] The O 1s core level moved toward
lower energy state from 5296 eV in P25 to 5294 eV in N-TiO2prepared with AT ratio 30 and calcined at 400∘C The
peak shifts by sim02 eV which might be related to the creationof oxygen vacancies as a result of the nitrogen doping Theshifting of bind energy in both N 1s and O 1s region indicatesthat nitrogen was incorporated into the lattice The shifts ofTi 2p32
and O 1s peaks are due to the introduction of oxygenvacancies into the TiO
2lattice [32] The presence of nitrogen
dopant facilitates the formation of oxygen vacancies Theaforementioned results clearly indicate that nitrogen dopingis accompanied by oxygen vacancy formation The opticaltransitions between the dopant and dopant-induced level andTi3d orbital explain the observed visible light absorptions ofN-TiO
2nanomaterials The observed two absorbance edge
features in the UV-vis spectra are directly related to the abovemodification of the electronic states from the dopants
50
40
30
20
10
00 05 1 15 2 25 3
AmmoniaTTIP molar ratio
Rem
oval
effici
ency
()
Calcination temp
400∘C
500∘C
800∘C
Figure 8 The removal efficiency of ethylene photooxidation overN-TiO
2as function of the various ammoniaTTIP molar ratios
Experimental conditions [C2H4] = 200 ppmv [H
2O]= 25060 ppmv
[O2] = 21 light intensity = 16mWcm2 temp = 30∘C reaction time
= 3 h
36 Visible Light Photocatalytic Activity To explore the pho-tocatalytic activity of different N-doped TiO
2at different
calcination temperatures and AT ratios the degradationof ethylene under visible light with a cut-off wavelengthof 400 nm was investigated Carbon dioxide started beingformed immediately after the visible light was turned on andethylene was almost totally converted to CO
2in all mea-
surements It is obviously that the N-TiO2shows significant
progress in the photodegradation of ethylene compared toP25 in visible light system P25 has no obvious photocatalyticactivity (less than 1) under visible light irradiation Resultssuggest modification of TiO
2provides visible-light-sensitive
photocatalyst which can be applied to the photooxidationof ethylene gas as the band gap of TiO
2was modified by
nitrogen doping evidenced by XPS and UV-visible DRSresults Figure 8 shows the activity of N-TiO
2catalysts in the
presence of visible light for photodegradation of ethyleneThe reaction rate increases with the increase in the AT ratiofrom 05 to 20 and then decreases in AT ratio from 20to 30 The enhancement of photocatalytic activity can beascribed to an obvious improvement in anatase crystallinityand larger surface area For the sample prepared with ATratio 20 and 30 however the removal efficiency decreasedrapidly which can be due to its less surface area Thephotocatalytic ability of N-TiO
2samples calcinated at 400
500 and 800∘C is also examined It was found that thephotocatalytic activity decreased with increasing calcinationtemperature The enhancement of photocatalytic activitycan be ascribed to an obvious improvement in anatasecrystallinity at 400∘C calcination temperature Good anatasecrystallization is beneficial for reducing the recombinationrate of the photogenerated electrons and holes due to thedecrease in the number of the defects [39] Zhao and Yangshowed that for photocatalytic oxidation application anataseis superior to rutile (a) the conduction band location foranatase is more favorable for driving conjugate reactions
International Journal of Photoenergy 11
32 eVCO2 + H2O
IntermediatesH2O
OH∙ C2H4
eminuseminusTiIII OH
TiIV OH
TiIV OH
O2
∙O2minus
∙HOO H2O2
TiIV OH+∙
CB
VBh+ NS
OV
Figure 9 Schematic diagram for the process in the photooxidation of ethylene and electron transfer process over N-TiO2under visible light
illumination
involving electrons and (b) very stable surface peroxidegroups can be formed at the anatase during photo-oxidationreaction but not on the rutile surface [40] For the samplecalcined at 800∘C the removal efficiency decreased rapidlywhich can be due to its fewer amounts of anatase andsmall 119878BET The result indicates that higher specific surfacearea smaller crystallite size and good anatase crystallizationwill promote the photocatalytic activity in visible light Theresults indicate the N-TiO
2catalyst prepared with AT ratio
20 and calcinated at 400∘C shows the best photocatalyticability
37 The Formation Mechanism of N-Doped TiO2 For the
pure TiO2 the energy of the visible light is not sufficient
to excite electrons from the valence band (VB) as theintrinsic band gap of pure TiO
2 Based on the results of UV-
vis DRS XRD and XPS the nitrogen atoms were weavedinto the crystal structure of TiO
2with structure as TindashOndash
N N-TiO2was active in the visible light irradiation for
the degradation of ethylene The following explanation forthe photocatalytic activity of N-TiO
2in the visible light
spectra can be consideredThe nitrogen existing at interstitialpositions of TiO
2lattice induces localized occupied states and
forms midband gap leading to the red shift of absorptionedge and photocatalytic activity under visible light irradiation[41] The electron (eminus) can be excited from the N-impuritylevel to the conduction band (CB) The exited electrons aretrapped by O
2adsorbed on the catalyst surface producing
O2
minus∙ superoxide anion radicals After a series of reactions(1)ndash(12) ethylene molecules are finally mineralized into CO
2
DFT calcinations and experimental results indicate that N-doping favored the formation of O vacancy (subband levelO119907) which was below the bottom of the conduction band
[42ndash47] Therefore the electrons (eminus) are excited from theN-impurity level bond to the subband level (O
119907) and then
recombine with the hole (h+) as proved in Figure 9 Theholes and electrons react with OHminus and O
2molecules on the
catalyst surface to form ∙OH radicals and O2
minus∙ superoxideanion radicals respectivelyThe protonation yields theHOO∙radicals which after trapping electrons combine to produceH2O2 The O
2
minus∙ radicals then interact with H2O adsorbed to
produce more ∙OH radicals These ∙OH radicals then reactwith gaseous ethylene and mineralize it
TiO2
h120592997888997888997888997888997888rarr h+ + eminus (1)
SndashH2O + h+ 997888rarr SndashOH∙ +H+ (2)
SndashOHminus + h+ larrrarr SndashOH∙ (3)
S1015840ndashO2+ eminus 997888rarr S1015840ndashO
2
minus∙ (4)
SndashOH + S1015840ndashO2
minus∙997888rarr SndashHO
2
∙+ S1015840ndashOminus∙ (5)
S1015840ndashO2997888rarr 2S1015840ndashO (6)
S1015840ndashO + eminus 997888rarr S1015840ndashOminus∙ (7)
SndashH2O + S1015840ndashOminus∙ 997888rarr SndashOH∙ + SndashOHminus (8)
SndashHO2
∙+ SndashHO
2
∙997888rarr SndashH
2O2+O2
(9)
SndashH2O2997888rarr 2SndashOH∙ (10)
SndashC2H4+ SndashOH∙ larrrarr SndashC
2H4OH (11)
SndashC2H4OH + S1015840ndashO
2997888rarr intermediates 997888rarr CO
2+H2O(12)
4 Conclusions
The observed changes in the UV-vis DRS XRD and XPSspectra are providing consistent structural information forTindashOndashN formation that is the nitrogen can be incorporatedinto the interstitial positions of TiO
2lattice which leads to
the enhanced photocatalytic activity in N-TiO2samples It
is concluded that the photocatalytic oxidation reactivity ofN-TiO
2under visible light illumination is mainly due to the
presence of localized occupied states caused by interstitialnitrogen and the electronhole pairs generated under visiblelight irradiation It has been found that N dopant retardedthe anatase to rutile phase transformation by forming TindashOndashN incorporated into the interstitial position of TiO
2lattice
Moreover the transformation temperatures of anatase-to-rutile progressively slightly increase when N dopant contentis increased The photocatalyst N-TiO
2prepared with AT
ratio 20 and calcinated at 400∘C shows the highest photo-catalytic activity in the oxidation of ethylene This N-TiO
2
provides an effective visible-light-responsive photocatalystfor future industrial applications in pollution control
12 International Journal of Photoenergy
Acknowledgment
This research was financially supported by the NationalScience Council of Taiwan ROC under Grant nos NSC-100-2221-E-005-007 and NSC-100-2120-M-005-002
References
[1] T Horikawa M Katoh and T Tomida ldquoPreparation and char-acterization of nitrogen-doped mesoporous titania with highspecific surface areardquo Microporous and Mesoporous Materialsvol 110 no 2-3 pp 397ndash404 2008
[2] K Yang Y Dai and B Huang ldquoStudy of the nitrogen concen-tration influence onN-dopedTiO
2anatase fromfirst-principles
calculationsrdquo Journal of Physical Chemistry C vol 111 no 32 pp12086ndash12090 2007
[3] K Pomoni A Vomvas and C Trapalis ldquoDark conductivity andtransient photoconductivity of nanocrystalline undoped andN-doped TiO
2sol-gel thin filmsrdquoThin Solid Films vol 516 no 6
pp 1271ndash1278 2008[4] S Sato ldquoPhotocatalytic activity of NO
119909-doped TiO
2in the
visible light regionrdquo Chemical Physics Letters vol 123 no 1-2pp 126ndash128 1986
[5] R Asahi T Morikawa T Ohwaki K Aoki and Y TagaldquoVisible-light photocatalysis in nitrogen-doped titaniumoxidesrdquo Science vol 293 no 5528 pp 269ndash271 2001
[6] J Ananpattarachai P Kajitvichyanukul and S Seraphin ldquoVisi-ble light absorption ability and photocatalytic oxidation activityof various interstitial N-doped TiO
2prepared from different
nitrogen dopantsrdquo Journal of Hazardous Materials vol 168 no1 pp 253ndash261 2009
[7] Y T Lin C HWeng and TW Tzeng ldquoPhotocatalysis and cat-alytic properties of nano-sized N-TiO
2catalyst synthesized by
Sol-gel methodsrdquo Journal of Advanced Oxidation Technologiesvol 13 no 3 pp 297ndash304 2010
[8] B Kosowska S Mozia A W Morawski B Grzmil M Janusand K Kałucki ldquoThe preparation of TiO
2-nitrogen doped by
calcination of TiO2sdot xH2O under ammonia atmosphere for
visible light photocatalysisrdquo Solar Energy Materials and SolarCells vol 88 no 3 pp 269ndash280 2005
[9] F Peng L Cai L Huang H Yu and H Wang ldquoPreparationof nitrogen-doped titanium dioxide with visible-light photocat-alytic activity using a facile hydrothermal methodrdquo Journal ofPhysics and Chemistry of Solids vol 69 no 7 pp 1657ndash16642008
[10] H Yu X Zheng Z Yin F Tag B Fang and K HouldquoPreparation of nitrogen-doped TiO
2nanoparticle catalyst and
its catalytic activity under visible lightrdquo Chinese Journal ofChemical Engineering vol 15 no 6 pp 802ndash807 2007
[11] Z Wang W Cai X Hong X Zhao F Xu and C CaildquoPhotocatalytic degradation of phenol in aqueous nitrogen-doped TiO
2suspensions with various light sourcesrdquo Applied
Catalysis B vol 57 no 3 pp 223ndash231 2005[12] A Trenczek-Zajac K Kowalski K Zakrzewska and M
Radecka ldquoNitrogen-doped titanium dioxidemdashcharacterizationof structural and optical propertiesrdquoMaterials ResearchBulletinvol 44 no 7 pp 1547ndash1552 2009
[13] J S Jang H G Kim S M Ji et al ldquoFormation of crystallineTiO2minus119909
N119909and its photocatalytic activityrdquo Journal of Solid State
Chemistry vol 179 no 4 pp 1067ndash1075 2006[14] H L Qin G B Gu and S Liu ldquoPreparation of nitrogen-doped
titania using sol-gel technique and its photocatalytic activityrdquo
Materials Chemistry and Physics vol 112 no 2 pp 346ndash3522008
[15] J Xu Y Ao D Fu andC Yuan J ldquoLow-temperature preparationof anatase titania-coated magnetiterdquo Journal of Physics andChemistry of Solids vol 69 pp 1980ndash1984 2008
[16] DWuM LongW Cai C Chen and YWu ldquoLow temperaturehydrothermal synthesis of N-doped TiO
2photocatalyst with
high visible-light activityrdquo Journal of Alloys andCompounds vol502 no 2 pp 289ndash294 2010
[17] K M Parida and B Naik ldquoSynthesis of mesoporous TiO2minus119909
N119909
spheres by template free homogeneous co-precipitationmethodand their photo-catalytic activity under visible light illumina-tionrdquo Journal of Colloid and Interface Science vol 333 no 1 pp269ndash276 2009
[18] N R Neti R Misra P K Bera R Dhodapkar S Bakardjievaand Z Bastl ldquoSynthesis of c-doped TiO
2nanoparticles by no-
vel sol-gel polycondensation of resorcinol with formaldehydefor visible-light photocatalysisrdquo Synthesis and Reactivity inInorganic Metal-Organic and Nano-Metal Chemistry vol 40no 5 pp 328ndash332 2010
[19] K Bubacz J Choina D Dolat E Borowiak-Palen D Mos-zynski and A W Morawski ldquoStudies on nitrogen modifiedTiO2photocatalyst prepared in different conditionsrdquoMaterials
Research Bulletin vol 45 no 9 pp 1085ndash1091 2010[20] Z Zhang X Wang J Long Q Gu Z Ding and X Fu
ldquoNitrogen-doped titanium dioxide visible light photocatalystspectroscopic identification of photoactive centersrdquo Journal ofCatalysis vol 276 pp 201ndash214 2010
[21] X Z Bu G K Zhang Y Y Gao and Y Q Yang ldquoPrepara-tion and photocatalytic properties of visible light responsiveN-doped TiO
2rectorite compositesrdquo Microporous and Meso-
porous Materials vol 136 no 1ndash3 pp 132ndash137 2010[22] C Liu X Tang C Mo and Z Qiang ldquoCharacterization and
activity of visible-light-driven TiO2photocatalyst codopedwith
nitrogen and ceriumrdquo Journal of Solid State Chemistry vol 181no 4 pp 913ndash919 2008
[23] R Kun S Tarjan AOszko et al ldquoPreparation and characteriza-tion of mesoporous N-doped and sulfuric acid treated anataseTiO2catalysts and their photocatalytic activity under UV and
Vis illuminationrdquo Journal of Solid State Chemistry vol 182 pp3076ndash3084 2009
[24] Z Pap L Baia K Mogyorosi A Dombi A Oszko and VDanciu ldquoCorrelating the visible light photoactivity of N-dopedTiO2with brookite particle size and bridged-nitro surface
speciesrdquo Catalysis Communications vol 17 pp 1ndash7 2012[25] X Z Bu G K Zhang and CH Zhang ldquoEffect of nitrogen dop-
ing on anatase-rutile phase transformation of TiO2rdquo Applied
Surface Science vol 258 pp 7997ndash8001 2012[26] Y P Peng E Yassitepe Y T Yeh I Ruzybayev S I Shah and C
P Huang ldquoPhotoelectrochemical degradation of azo dye overpulsed laser deposited nitrogen-doped TiO
2thin filmrdquo Applied
Catalysis B vol 125 pp 465ndash472 2012[27] H Jie H B Lee K H Chae et al ldquoNitrogen-doped
TiO2nanopowders prepared by chemical vapor synthesis
band structure and photocatalytic activity under visible lightrdquoResearch on Chemical Intermediates vol 38 no 6 pp 1171ndash11802012
[28] S U M Khan M Al-Shahry and W B Ingler ldquoEfficientphotochemical water splitting by a chemically modified n-TiO2rdquo Science vol 297 no 5590 pp 2243ndash2245 2002
International Journal of Photoenergy 13
[29] X X Wang S Meng X L Zhang H T Wang W Zhong andQ G Du ldquoMulti-type carbon doping of TiO
2photocatalystrdquo
Chemical Physics Letters vol 444 pp 292ndash296 2007[30] N R Khalid E Ahmed Z L Hong Y W Zhang and
M Ahmad ldquoNitrogen doped TiO2nanoparticles decorated
on graphene sheets for photocatalysis applicationsrdquo CurrentApplied Physics vol 12 no 6 pp 1485ndash1492 2012
[31] Q J Xiang J G Yu and M Jaroniec ldquoNitrogen and sulfurco-doped TiO
2nanosheets with exposed 001 facets synthesis
characterization and visible-light photocatalytic activityrdquo Phys-ical Chemistry Chemical Physics vol 13 no 11 pp 4853ndash48612011
[32] J Wang D N Tafen J P Lewis et al ldquoOrigin of photocatalyticactivity of nitrogen-doped TiO
2nanobeltsrdquo Journal of the
American Chemical Society vol 131 pp 12290ndash12297 2009[33] Q Xiang J YuWWang andM Jaroniec ldquoNitrogen self-doped
nanosized TiO2sheets with exposed 001 facets for enhanced
visible-light photocatalytic activityrdquoChemical Communicationsvol 47 no 24 pp 6906ndash6908 2011
[34] Y C Tang X H Huang H Q Yu and L H Tang ldquoNitrogen-doped TiO
2photocatalyst prepared by mechanochemical
method doping mechanisms and visible photoactivity of pol-lutant degradationrdquo International Journal of Photoenergy vol2012 Article ID 960726 10 pages 2012
[35] D E Gu Y Lu B C Yang and Y D Hu ldquoFacile preparationof micro-mesoporous carbon-doped TiO
2photocatalysts with
anatase crystalline walls under template-free conditionrdquo Chem-ical Communications no 21 pp 2453ndash2455 2008
[36] W Ren Z Ai F Jia L Zhang X Fan and Z Zou ldquoLow tem-perature preparation and visible light photocatalytic activity ofmesoporous carbon-doped crystalline TiO
2rdquo Applied Catalysis
B vol 69 no 3-4 pp 138ndash144 2007[37] EM Rockafellow X Fang B G Trewyn K Schmidt-Rohr and
W S Jenks ldquoSolid-state 13C NMR characterization of carbon-modified TiO
2rdquo Chemistry of Materials vol 21 no 7 pp 1187ndash
1197 2009[38] Y Zhang P Xiao X Zhou D Liu B B Garcia and G Cao
ldquoCarbon monoxide annealed TiO2nanotube array electrodes
for efficient biosensor applicationsrdquo Journal of Materials Chem-istry vol 19 no 7 pp 948ndash953 2009
[39] J Yu L Zhang B Cheng andY Su ldquoHydrothermal preparationand photocatalytic activity of hierarchically sponge-like macro-mesoporous Titaniardquo Journal of Physical Chemistry C vol 111no 28 pp 10582ndash10589 2007
[40] J Zhao and X Yang ldquoPhotocatalytic oxidation for indoor airpurification a literature reviewrdquo Building and Environment vol38 no 5 pp 645ndash654 2003
[41] C Di Valentin G Pacchioni and A Selloni ldquoOrigin of thedifferent photoactivity of N-doped anatase and rutile TiO
2rdquo
Physical ReviewB vol 70 no 8 Article ID 085116 4 pages 2004[42] S Livraghi M C Paganini E Giamello A Selloni C
Di Valentin and G Pacchioni ldquoOrigin of photoactivity ofnitrogen-doped titanium dioxide under visible lightrdquo Journal ofthe American Chemical Society vol 128 no 49 pp 15666ndash156712006
[43] X Chen and C Burda ldquoThe electronic origin of the visible-lightabsorption properties of C- N- and S-doped TiO
2nanomateri-
alsrdquo Journal of the American Chemical Society vol 130 no 15pp 5018ndash5019 2008
[44] C Di Valentin G Pacchioni and A Selloni ldquoTheory of carbondoping of titanium dioxiderdquo Chemistry of Materials vol 17 no26 pp 6656ndash6665 2005
[45] HWang and J P Lewis ldquoEffects of dopant states on photoactiv-ity in carbon-dopedTiO
2rdquo Journal of Physics CondensedMatter
vol 17 no 21 pp L209ndashL213 2005[46] H Li D Wang H Fan P Wang T Jiang and T Xie ldquoSynthesis
of highly efficient C-doped TiO2photocatalyst and its photo-
generated charge-transfer propertiesrdquo Journal of Colloid andInterface Science vol 354 no 1 pp 175ndash180 2011
[47] ZWu FDongWZhao and SGuo ldquoVisible light induced elec-tron transfer process over nitrogen doped TiO
2nanocrystals
prepared by oxidation of titaniumnitriderdquo Journal of HazardousMaterials vol 157 no 1 pp 57ndash63 2008
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
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International Journal ofPhotoenergy
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Journal of
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Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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CatalystsJournal of
2 International Journal of Photoenergy
absorption activity not only was shifted toward the longervisible wavelength but also had higher thermal stability andless recombination centers of charge carries than the metal-doped TiO
2[5] However to date little research has been
conducted on gaining in-depth information on the propertiesof the interstitial (or substitutional) N-doped TiO
2 as well as
its photocatalytic activity Different dopants result in TiO2of
different properties and consequently alter the photocatalyticactivity of the materials Currently few works have focusedon the synergistic effects of nitrogen dopant and calcinationtemperature on the characteristics and visible-light-inducedphotoactivity of N-doped TiO
2[6]
In this study we focused on sol-gel synthesis process forthe preparation of nitrogen-doped TiO
2catalysts (N-TiO
2)
because the wet processes have the advantages of low costease of scale-up and stablility for practical applications Theeffects of N atom and calcination temperature on the struc-tural optical and photocatalytic properties of N-TiO
2were
assessedThe gel samples were calcined at 400 500 600 700and 800∘C The photocatalysts were characterized using X-ray diffraction (XRD) high-resolution transmission electronmicroscope (HRTEM) X-ray photoelectron spectroscopy(XPS) UV-vis diffusion reflectance spectroscopy (UV-visDRS) Brunauer-Emmett-Teller (BET) specific surface area(119878BET) and thermogravimetric-differential thermal analysis(TG-DTA) The transition from amorphous to anatase andrutile phases at different calcination temperatures was alsoexplored Ethylene was chosen as a probe reactant becauseit is structurally simple has relatively high reactivity and isthe parent compound of many widespread volatile organiccompounds (VOCs) of environmental concern (eg TCE andtetrachloroethylene) The object of this study is to investigatethe synergistic effects of nitrogen content and calcinationtemperatures in the synthesis process of N-doped TiO
2
prepared by sol-gel process and to investigate the influenceof ethylene on photocatalytic decomposition
2 Materials and Methods
21 Preparation of N-Doped TiO2Catalyst Titanium iso-
propoxide (TTIP C12H28O4Ti 97 Aldrich) a highly re-
active alkoxide was used as precursor Aqua ammonia(NH4OH) was used as nitrogen source A given amount of
aqua ammonia was added to the distilled water while beingstirred until it completely dissolved at room temperatureThen the solution was added dropwise to a constant amountof titanium isopropoxide as to obtain an aqua ammoniato TTIP molar ratio (AT) of 1 1 the TiO
2sample was
designated as N-TO2 While the mixture was being stirred
vigorously the urea solution was introduced to the TTIPHydrolysis and ploycondensation reactions occurred Thereactant was stirred continuously for one hour after all aquaammonia solution was dissipated The sol was aged in air for24 hr to allow further hydrolysis The final sol was left on thebench top to allow thickening After aging the sol was driedat 70∘C for 24 hr to evaporate the solventThe residual xerogelwas crushed to fine powder before calcined in a furnace at400 500 600 700 and 800∘C respectively for 3 hr Pure
TiO2powder was also prepared without the presence of aqua
ammonia following the same procedures as described aboveThe nitrogen-doped samples were labeled AxTy where 119909and 119910 refer to the aqua ammonia to TTIP molar ratio (AT)and calcining temperature respectively For example A20T4means the N-TiO
2prepared with AT molar ratio 20 and
calcinated at 400∘C
22 Characterization The 119878BET of the samples was deter-mined using nitrogen adsorption method measured with aMicromeritics ASAP 2020 adsorption apparatus Pore sizeand pore volume were calculated by the BJH isotherm Thecrystallization behavior and stability of N atoms in N-TiO
2
were monitored using a TG-DTA (STA 6000 PerkinElmer)while the sample was being heated from room temperatureto 1000∘C at 10∘CminThe morphology structure and grainsize of the samples were characterized by a high-resolutiontransparent electromicroscopy (HRTEM JEM-2010 JEOL)To study the optical response of N-TiO
2samples (120582 = 200ndash
800 nm) UV-vis DRS (U3900H Hitachi) were recordedusing a spectrophotometer with an integrating sphere attach-ment and Al
2O3was used as the reference The chemical
environment information and the N concentration of all ofthe samples were measured by X-ray photoelectron spectra(XPS) (PHI 5000 VersaProbeScanning ESCA Microprobewith aC
60ion gun) All sampleswere collected in vacuumand
transferred to the main ultrahigh-vacuum (UHV) chamberfor measurements The shift of binding energy due to relativesurface charging was corrected to the C 1s level at 285 eV asan internal standard The XPS peaks were assumed to haveGaussian line shapes and were resolved into components by anonlinear least-squares procedure after proper subtraction ofthe baseline The crystallinity and phase of the samples wereanalyzed byXRD (PANalytical XrsquoPert-ProMPDPW304060)with Cu-Ka radiation at a scan rate of 005∘ 1s in the rangefrom 20 to 80∘
23 Photooxidation Performance The experiment setup andoperating conditions for photocatalytic activity tests werethe same as those reported previously [7] The catalyst wasprepared by depositing suspension of the as-prepared catalystat the bottom surface of the reactor that was subsequentlydried at ambient conditionThe obtained catalyst film densityon the bottom surface of reactor was kept at 4mgcm2 Theexperiment setup and operating conditions for photocat-alytic activity tests were the same as those in our previousreports [7] The photocatalytic activity experiments of theas-prepared catalysts for the oxidation of ethylene in gasphase were performed at room temperature using a 250mLphotocatalytic reactor Air with 60 relative humidity waspassed through the reactor with the sample inside for 1 hrto reach equilibrium and then a desired amount of ethylenewas injected into the reactor with a gastight syringe Theethylene inside the reactor was taken at regular intervals withgas-tight syringe and analyzed using gas chromatographs(PerkinElmer Clarus 500 USA) equipped with a flameionization detector (FID) and a thermal conductivity detector(TCD) detection The GC instrument was equipped with an
International Journal of Photoenergy 3
Elite-Plot-Q capillary column (Agilent Technologies) Theethylene was allowed to reach adsorption equilibrium withthe catalyst in the reactor prior to irradiation Two 500-W horizontal halogen lamps (95 cm in length PHILIPS)were used to simulate the solar light The lamp equippedwith a cut-off filter (120582 gt 400 nm) was vertically placedoutside the photocatalytic reactor Light intensity at thecatalyst surface was 16mWcm2 Blank experiments usingan uncoated (no catalyst) glass plate had no effect on theethylene concentration and did not generate any carbonmonoxide or carbon dioxide (see supplementary materialonline at httpdxdoiorg1011552013268723) The photo-catalytic activity of the catalyst can be quantitatively evaluatedby comparing the apparent reaction rate constants
3 Results and Discussion
31 Thermal Analysis To investigate the process of phasetransformation of titanium(IV)-oxide-hydroxide to titaniumoxide and the effect of nitrogen doping content on thetransformation from anatase to rutile thermoanalytic tech-niques including TGA and DTA were conducted Typicallythe hydrothermal weight loss is attributed to a multistepof polycondensation of titanium(IV)-oxide-hydroxide andphase transformation of anatase into rutile or brookite fromroom temperature to 700ndash800∘C as shown in Figure 1 andTable 1 DTA measurements established the transformationof TiO
119909(OH)119910into TiO
2including two endothermic and
one exothermic peaks from room temperature to 398∘C(Figure 1) A sharp endothermic peaks at 105∘C due to therelease of absorbed water while the other minor peak at253∘C is referred to as the desorption of organic Therewas a corresponding weight loss from TGA of about 198and 94wt respectively In the region mentioned abovethe finely exothermic peak around 276∘C is ascribed to thethermal decomposition of unhydrolyzed TTIP with about08 wt weight loss The weak thermal effect at 276ndash730∘Cis accompanied by obvious exothermic peak at 451∘C whichcan be assigned to the crystallization of the amorphous phaseto anatase At around 730∘C an obvious exothermic peakwas observed owing to the oxidation of carbon residue andevaporation of chemisorbed water which can be assignedto the phase transformation from anatase titania to rutileTiO2 It can be concluded from the DTA result that the as-
prepared TiO2sample was amorphous According to TGA
the weight loss roughly consists of three distinct stages Thefirst stage was up to 276∘C over which the mass loss is thegreatest A mass loss of up to 30 was observed which isattributed to the evaporation of the physical adsorbed waterand the release of organic The second stage is from 276 to451∘C where the mass loss is about 17This corresponds tothe thermal decomposition of unhydrolyzed TTIP The thirdstage is from 451 to 730∘C and the mass loss is about 07which is attributed to the removal of chemisorbed water Atabout 730∘C no mass loss was observed The exothermicpeaks of N-TiO
2prepared at 05 10 and 20 AT ratios
were at 710 720 and 730∘C respectively (Table 1)The resultsindicated that nitrogen atoms doped in TiO
2could prevent
100
80
60
40
20
0
60
50
40
30
20
10
00 100 200 300 400 500 600 700 800
Wei
ght l
oss (
)
Hea
t flow
(mW
mg)
Temperature (∘C)
198 94 17 07
105∘ C
253∘ C
276∘ C
451∘ C
730
∘ C
Anatase into rutile
Release of adsorbed water
Desorption of organics
Amorphous into anatase
Thermal decomposition of unhydrolyzed TTIP
Figure 1 TG-DTA curve of N-TiO2samples prepared with 20
ammoniaTTIP ratio
phase transition of anatase to rutile because as far as pureTiO2was concerned most TiO
2particles were transformed
into rutile at 700∘C
32 Phase and Structure The characteristics of N-TiO2at
various calcination temperatures and molar ratios of ATare summarized in Table 1 Figure 2 shows the XRD patternof the N-TiO
2samples at various AT ratios and annealed
at different temperatures The presence of peaks (2120579 =2544∘ 3806
∘ and 4824∘) was regarded as an attributive
indicator of anatase titania and the presence of peaks (2120579 =2754∘ 3614
∘ and 4120∘) was regarded as an attributive
indicator of rutile titaniaThediffraction peaks for the anatase(JCPDSno 21-1272) and rutile (JCPDSno 21-1276) phases aremarked with ldquoArdquo and ldquoRrdquo respectively and the correspondingdiffraction planes are given in parenthesis No N-derivedpeaks were detected in all the patternsThismay be caused bythe lower concentration of the doped species and the limiteddopants may have moved into either the interstitial positionsor the substitutional sites of the TiO
2crystal structure which
is consistent with [8 9] The average grain size was estimatedat 28ndash131 nm comparable to that from the HRTEM imageA comparison of XRD patterns clearly shows that nitrogendoping significantly changes the crystalline size and thecrystal structure of TiO
2
The transformation from the amorphous to the crys-talline form of TiO
2usually requires temperatures close
to 300∘C [8] For the samples prepared with 20 AT andcalcinated at 400ndash500∘C (Figure 2(a)) the intensities ofthe anatase peak are increased and the width of the (101)plane diffraction peak becomes narrower as the calcinationtemperature increases implying an improvement and growthin crystallinity Increasing the temperature to 800∘C theintensity of anatase peak decreases but the rutile peaksappear suggesting the transformation of anatase to rutilephase The average crystalline size was 32 85 and 103 nmand the mass percentage of anatase was 90 60 and 6 forsamples prepared at 20 AT and calcination temperature
4 International Journal of Photoenergy
Table 1 Characteristics for N-TiO2 at various ammoniaTTIP molar ratios under different calcination temperatures
SampleaXRD BET TG-DTA TEM Optical properties
Phase ratio Crystallite size Surface area (m2g) Abrarr Rc Temp (∘C) Size (nm) 1205821198921 1198641198921 1205821198922 1198641198922
Ab Rc Ab (nm) Rc (nm) (nm) (nm) (nm) (nm)A00T4 90 10 32 mdash 93 703 11 plusmn 1 392 316 mdash mdashA05T4 89 11 28 mdash 108 710 12 plusmn 1 392 316 505 246A10T4 90 10 28 mdash 119 720 12 plusmn 1 391 317 506 245A15T4 87 13 29 mdash 119 728 11 plusmn 1 388 320 513 242A20T4 90 10 32 mdash 98 730 12 plusmn 1 390 318 510 243A25T4 90 10 37 mdash 98 728 12 plusmn 1 392 316 515 241A30T4 92 8 37 mdash 86 729 12 plusmn 1 392 316 514 241A00T5 94 6 46 mdash 50 703 13 plusmn 2 402 308 mdash mdashA05T5 89 11 46 98 64 710 13 plusmn 1 404 307 503 247A10T5 90 10 41 87 68 720 15 plusmn 2 400 310 508 244A15T5 91 9 40 mdash 71 728 15 plusmn 2 396 313 517 240A20T5 94 6 45 mdash 62 730 15 plusmn 2 394 315 513 242A25T5 94 6 49 mdash 55 728 17 plusmn 2 397 312 507 245A30T5 94 6 47 mdash 53 729 17 plusmn 2 397 312 510 243A00T6 34 66 106 156 7 703 24 plusmn 2 420 295 mdash mdashA05T6 14 86 86 128 8 710 40 plusmn 3 422 294 mdash mdashA10T6 14 86 81 132 9 720 40 plusmn 4 425 292 mdash mdashA15T6 22 78 79 141 14 728 35 plusmn 3 424 292 mdash mdashA20T6 60 40 85 184 17 730 34 plusmn 3 415 299 mdash mdashA25T6 78 22 90 184 16 728 35 plusmn 4 416 298 mdash mdashA30T6 74 26 97 169 12 729 36 plusmn 4 415 299 mdash mdashA00T7 6 94 131 177 2 703 80 plusmn 5 424 292 mdash mdashA05T7 3 97 95 148 5 710 145 plusmn 10 428 290 mdash mdashA10T7 3 97 102 149 6 720 145 plusmn 10 429 289 mdash mdashA15T7 3 97 92 159 6 728 150 plusmn 11 428 290 mdash mdashA20T7 6 94 103 163 4 730 170 plusmn 13 428 290 mdash mdashA25T7 15 85 108 178 8 728 60 plusmn 6 426 291 mdash mdashA30T7 15 85 117 182 6 729 60 plusmn 6 427 290 mdash mdashA00T8 1 99 mdash 174 3 703 200 plusmn 17 424 292 mdash mdashA05T8 1 99 mdash 161 3 710 190 plusmn 15 428 290 mdash mdashA10T8 1 99 mdash 159 3 720 160 plusmn 13 429 289 mdash mdashA15T8 1 99 mdash 171 3 728 170 plusmn 15 428 290 mdash mdashA20T8 1 99 mdash 164 2 730 160 plusmn 14 428 290 mdash mdashA25T8 3 97 106 184 4 728 200 plusmn 18 427 290 mdash mdashA30T8 3 97 127 179 3 729 170 plusmn 15 429 289 mdash mdashaAXXTY ammoniaTTIP molar ratio = 0XX calcination temperature = Y00∘CbAnatasecRutile
of 400 600 and 700∘C respectively The maximum meansize of anatase and rutile crystallites was observed at 800∘CResults agreed with those reported that the crystalline sizegrows and the content of anatase diminishes as calcinationtemperature increases [8 10ndash13] For the samples prepared at05 AT the anatase peaks appear at temperatures 400 and500∘C Increasing the temperature to 500∘C the intensity ofanatase peak decreases but the rutile peaks appear Whentemperature is increased further to 600∘C rutile becomesa main phase In this case the anatase-to-rutile phasetransformation temperature is between 400 and 500∘C XRD
patterns of samples prepared at 30 AT and annealed at700∘C show both anatase and a rutile phase indicating thatanatase-to-rutile phase transformation is shifted to highertemperature It can be seen that the presence of nitrogencan restrain the formation and growth of TiO
2crystal phase
thereby retarding the anatase-to-rutile phase transformationThis result is further supported by the appearance of rutilein XRD patterns of sample prepared at 05 and 15 GTat 600∘C and disappearance for samples prepared at GTgreater than 20 at 600∘C (data not shown) Comparedwith P25 the peak position of the (101) plane of N-doped
International Journal of Photoenergy 5
A A A
A A
AR
R
RR R R
(101) (110) (004) (204)(200)
(105)(211)
(101)
(111)
(210) (211) (220)
Inte
nsity
(au
)
20 30 40 50 60 70 80
Calcination temperature (∘C)400
500
600
700
800
2120579 (deg)
AT ratio 2
(a)
A A A A A A(101) (004) (204)(200)(105)(211)
Inte
nsity
(au
)
20 30 40 50 60 70 80
0051
15
2253
2120579 (deg)
AT ratio
Calcination temperature 400∘C
P25
(b)
Figure 2 XRD patterns of N-TiO2samples prepared (a) at various calcination temperatures and (b) with various ammoniaTTIP ratios
TiO2shifted slightly to higher 2120579 value and the peak was
broader as NT ratio increases suggesting distortion of thecrystal lattice of TiO
2by the incorporation of nitrogen The
crystalline sizes of samples calcinated at 400∘C and pre-pared at 05 15 20 and 30 AT were 28 29 32 and37 nm respectively The average crystalline size of samplesincreases with increase in AT revealing that nitrogen canenhance the growth of N-TiO
2crystals Results agreed with
those reported that the crystalline size grows as nitrogento Ti proportion increases [14] The results reveal that thephase transformation temperature of anatase to rutile wasprogressively increased when the amount of N dopant wasincreased Clearly calcination temperature andAT ratio playa significant role in the formed crystal structure and particlesize (Figure 3)Higher temperature favors the growth of rutilestructure and produces N-TiO
2nanoparticles with larger
particle size Thus a fine control of calcination temperatureand AT ratio is crucial for obtaining a pure phase of N-TiO
2
Further insights into the effect of calcination and dopingon the morphology and structure of the N-TiO
2samples can
be obtained from HRTEM image (Figure 4) The selectedarea electron diffraction pattern and TEM confirmed itshighly crystalline anatase or rutile structure The observedd-spacing from HRTEM image is 3522 A and is comparableto 352 A previously reported for (101) crystallographic planeof undoped anatase [15ndash18] The HRTEM image showedthe nanocrystallines with primary grain size around 11ndash200 nm From the TEM images the particles in N-TiO
2
samples are monodispersed The crystalline form aggregateswith a mesoporous structure The formation of mesoporousstructure is similar to that reported in the literature [1920] First monodispersed amorphous titanium oxide solparticles are formed by the hydrolysis processes Then themonodispersed sol particles are crystallized and aggregatedunder calcination treatment to form mesoporous crystallineBased on the HRTEM results the calcination temperature
100
80
60
40
20
0400 500 600 700 800Calcination temperature (∘C)
AmmoniaTTIP molar ratio
Ana
tase
()
005115
2253
Figure 3 The anatase content of N-TiO2samples as a function of
the various ammoniaTTIP molar ratios
significantly changes the size of particles (Table 1) The grainsize of crystalline is in consistent with the calculated valueobtained from XRD patterns (Table 1) The grain size ofsamples increases with the calcination temperatureMorpho-logical observation by TEM and XRD calculations revealsthat the large particle size of A20T8 was mainly caused byagglomeration and the growth of crystallite size
33 Surface Area and Pore Size Distribution Typical nitrogenadsorption-desorption isotherms of N-TiO
2photocatalyst
6 International Journal of Photoenergy
400∘C
10nm
(a)
500∘C
10nm
(b)
600∘C
50nm
(c)
700∘C
50nm
(d)
100nm
800∘C
(e) (f)
Figure 4 TEM images of N-TiO2prepared (a)ndash(e) at various calcination temperatures with 20 ammoniaTTIP ratio and (f) the selected
area electron diffraction of A20T4
are shown in Figure 5 The 119878BET of N-TiO2prepared with 20
AT ratio at calcined 400 500 600 700 and 800∘C was 9862 17 4 and 2m2g respectively Obviously the values of119878BET and pore volume of N-TiO
2prepared with the same AT
ratio decreased with increasing calcination temperaturesSuch phenomenon could be attributed to the collapse of themesoporous structure the growth of TiO
2crystallites and
the removal process of nitrogen core by high-temperaturecalcination Consequently N-TiO
2calcined at 800∘C has the
least 119878BET Based on the results obtained the hysteresis loop ofN-TiO
2is significantly shifted in direction of higher relative
pressures as calcination temperature increases indicatingmuch larger mesorpore The average pore size of N-TiO
2
increased with increasing calcination temperature due to theformation of slit-like pores [21]
The N-TiO2samples obtained at various calcination
temperatures gave different nitrogen adsorption isotherms(Figure 5) implying differences in their porous structureThe N-TiO
2samples prepared at low calcination temperature
(ie 400 and 500∘C) exhibited a type IV isotherm and atype H2 hysteresis loop at lower relative pressure regionwhich are typical characteristics of mesoporous structurewith ink bottle pores Note that the adsorption branches ofthese isotherms resembled type II indicating the presence ofsome macropores Otherwise the N-TiO
2samples prepared
at higher calcination temperature (ie 600ndash800∘C) exhibiteda type V isotherm and a type H3 hysteresis loop at higherrelative pressureThe hysteresis loop at lower relative pressureregion (04 lt 119875119875
0lt 08) was attributed to a smaller mes-
opore while that at the higher relative pressure (08 lt1198751198750lt 10) was of larger mesopores Thus samples prepared
at high calcination temperature (gt600∘C) had a wide poresize distribution in the mesopores scale The isotherm of N-TiO2prepared at higher calcination temperature was below
that of lower calcination temperature (Figure 5) indicatinglower surface area and pore volume of the former Furtherobservation from Table 1 indicated that 119878BET for the N-TiO
2
samples at the same AT ratio increased with increasingcalcination temperature (Figure 5(c)) Results reveal thatall N-TiO
2samples calcined at various temperatures show
monomodal pore size distributions and mesopores may beassigned to the pores among interaggregated particles (datanot shown) With calcination temperature increasing thereis a significant tendency of pore size distribution toward tothe bigger pore size The increase of pore size is due to thecorruption of smaller pores during calcination as the smallerpores endured much greater stress than the bigger poresFormation of bigger crystalline aggregation upon increasein temperature could form bigger pores also Consequentlythe pore size increases while the pore volume decreases with
International Journal of Photoenergy 7
200
150
100
50
00 02 04 06 08 1
400500600
700800
IV
IV
V
VV
AmmoniaTTIP ratio 2Calcination temperature (∘C)
Qua
ntity
adso
rbed
(cm
3g
STP
)
Relative pressure (1198751198750)
(a)
0 02 04 06 08 1
005115
2253
IV
250
200
150
100
50
0
H3
Calcination temperature 400∘CAmmoniaTTIP ratio
Qua
ntity
adso
rbed
(cm
3g
STP
)
Relative pressure (1198751198750)
(b)
0
120
100
80
60
40
20
0400 500 600 700 800
Calcination temperature (∘C)
Surfa
ce ar
ea (m
2g
)
05115
2253
AmmoniaTTIP ratio
(c)
Figure 5 Nitrogen adsorption and desorption isotherms of N-TiO2samples (a) calcined at various temperatures (b) prepared with various
ammoniaTTIP molar ratios the surface area as a function of calcination temperature
calcinations temperature increasing Based on the TEM andBET results the mesopores of TiO
2were decreased due
to the heat shrinkage of calcination The results indicatedthat calcination at high temperature and in the presence ofnitrogen atoms will help to improve the thermal stabilityof the photocatalyst While the calcination temperature wasincreased both the specific surface area and the pore vol-ume of N-TiO
2samples decreased This indicated that the
average pore size increased while the pore volume and the
specific surface area decreased with calcination temperatureincreasing
34 Optical Properties The typical UV-vis diffuse reflectancespectra of N-TiO
2are shown in Figures 6(a) and 6(b) It can
be seen that nondoped TiO2(P25) has only one light sharp
edge (120582 = 410 nm) which can be assigned to the band gapof TiO
2 while part of N-TiO
2showed two absorption edges
and a noticeable shift to the visible light region as compared
8 International Journal of Photoenergy
400500600
700800
2
15
1
05
0
Abso
rban
ce (a
u)
Abso
rban
ce (a
u)
200 300 400 500 600 700 800Wavelength (nm)
Wavelength (nm)Calcination temp (∘C)
05
04
03
02
01
0350 400 450 500 550
NTi 2 molar ratiocalcination at different temperatures
AT ratio 2
A20T4A20T5A20T6A20T7A20T8
P25
(a)
2
15
1
05
0
Abso
rban
ce (a
u)
200 300 400 500 600 700 800Wavelength (nm)
Abso
rban
ce (a
u)
Wavelength (nm)
04
04
03
03
02
02
01
01380 400 420 440 460 480 500 520 540
Calcination at 400∘C temperaturedifferent NTi molar ratios
325
215
1050P25
A00T4A05T4A10T4A15T4
A20T4A25T4A30T4
AT ratio
Calcination temperature 400∘C
(b)
Figure 6 The typical UV-vis DR spectra of N-TiO2samples (a) prepared with 20 ammoniaTTIP molar ratio and calcined at various
temperatures (b) prepared with various ammoniaTTIP molar ratios and calcined at 400∘C
to that of the TiO2(ie P25) This phenomenon should be
ascribed to either the nitrogen doping andor sensitizationby a surface-anchored group The calcination temperatureand AT ratio are the crucial factor that can further affectthe absorption as seen in Figure 6 Similar phenomenonhad been reported by previous publications [17 22ndash25] Theabsorption edges of the N-TiO
2samples show continuous
red shift as the calcination temperature changes from 400to 700∘C which can be assigned to the intrinsic band gapabsorption of TiO
2 The shift is too minor to be observed
when the calcination temperature changes from500 to 600∘Cwhich is possibly caused by the synergetic effect of the loss ofthe nitrogen and the increase of the TiO
2crystallinity during
the calcination processThe absorption threshold (120582119892) can be
determined using the onset of the absorption edges by thesection of the fitting lines on the upward and outward sectionof the spectrum (shown in the graph inserted in Figure 6)[23] Table 1 lists the determined 120582
119892(nm) and the derived
band gap energy values The band gap of N-TiO2(119864119892) was
calculated using the 119864119892= 1240120582
119892equation It also can be
seen that N-TiO2samples have two characteristic light
absorption edges One of them corresponds to the band gapof TiO
2(1205821198921= 390sim430 nm) while the other originates from
the N-induced midgap level (1205821198922= 505sim517 nm) The color
of the samples was different with calcination temperatureand AT ratio The color of N-TiO
2samples prepared with
20 AT ratio and calcinated at 400 600 and 700∘C wasvivid yellow yellow and white respectively There is no 120582
1198922
when N-TiO2calcinated above 600∘C It can be ascribed to
the amount of N dopant decreased The color of N-TiO2
prepared with 00 10 20 and 30 AT ratio and calcinatedat 400∘C was white pale yellow yellow and vivid yellow
respectively The phenomenon that the AT ratio increasesthe shifting of the spectra towards visible region was clearlyobserved (Figure 6(a)) The absorption threshold (120582
119892) was
increased with increasing AT ratio It reveals that morenitrogen doping in the matrix of TiO
2structure results in a
shift of absorbance region toward visible light wavelengthThis is possible attribute to the nitrogen incorporated intoTiO2lattice and formation of new electronic state above
valence band caused by nitrogen doping to generate a redshift
35 Analysis of Chemical State The chemical states of dopingimpurity are critical to the optical property band gap andphotocatalytic activity of nitrogen-dopedTiO
2 To investigate
the chemical states of the doping nitrogen XPS spectra wereapplied to examine three regions the Ti 2p core level near460 eV the O 1s core level near 530 eV and the N 1s core levelnear 400 eV Figure 7 shows the experimental observation ofsurface chemical composition and the electronic structuresof N-TiO
2samples using XPS XPS peaks showed that the N-
TiO2contained only Ti O N elements and a small quantity of
carbon The presence of carbon was ascribed to the residualcarbon from the precursor solution and the adventitioushydrocarbon from the XPS instrument itself In Figures 7(a)and 7(b) the binding energy (BE) peaks corresponding toN 1s core levels for N-TiO
2are observed one major peak at
400 eV The N 1s peak at 400 eV is ascribed to the presenceof the oxidized nitrogen species and the nitrogen may beincorporating into the interstitial positions of the TiO
2lattice
and to form a TindashOndashN structure [26 27] No other N 1s peakswere detected in N-TiO
2samples As shown in Figure 7 N 1s
peak at 400 eV slightly decreased with increasing calcination
International Journal of Photoenergy 9
Bind energy (eV)
Inte
nsity
(au
)800
700
600
500
400
Calcination temp (∘C)Ti-O-N
390 395 400 405 410
AT ratio 2
(a)
Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
325
2
15
1
05
0
Ti-O-N
390 395 400 405 410
AT ratio
(b)
Bind energy (eV)
Inte
nsity
(au
) 800
700
600
500
400
Calcination temp (∘C)
Ti-O
524 526 528 530 532 534 536
AT ratio 2
(c)
Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
3
25
2
15
1
05
0
Ti-O
524 526 528 530 532 534 536
AT ratio
(d)
454 456 458 460 462 464 466 468Bind energy (eV)
Inte
nsity
(au
)
4582
4581
4583
458
4583
800
700
600
500
400
Calcination temp (∘C)AT ratio 2Ti4+2p32
Ti4+2p12
(e)
454 456 458 460 462 464 466 468Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
3
25
2
15
1
05
0
Ti4+2p32
Ti4+2p12 AT ratio
(f)
Figure 7 XPS survey and core level spectra of (a)-(b) N 1s (c)-(d) Ti 2p and (e)-(f) O 1s of N-TiO2samples
temperature This is different from the N-TiO2prepared by
flame oxidation in which nitrogen partially substitutes theoxygen sites in the TiO
2[28] The preparation method plays
an important role in determining the nitrogen state in TiO2
band structure [26 29 30]Depending on the nitrogen source
and experimental conditions N species are incorporated intoTiO2in interstitial form or substitutional form [31 32] The
interstitial N-doping is favored when the doping is carriedout under oxygen-rich conditions and the substation-typeN-doping occurs under reducing conditions [31ndash33] Therefore
10 International Journal of Photoenergy
from the atomicN 1sXPS spectra the interstitial sites (400 eV)were observed under air atmosphere
The XPS spectra of Ti 2p regions are shown in Figures7(c) and 7(d) The peaks at around 4585 and 4642 eV forP25 are ascribed to Ti 2p
32and Ti 2p
12of TiO
2(data not
shown)The line separation between Ti 2p12
and Ti 2p32
was57 eV which is consistent with the standard binding energyAccording to Figure 7 all spectra of Ti 2p
12are symmetry
The spectra of Ti 2p12
are consistent of single state and thebanding energy of peaks is 4580ndash4583 eV which shows aredshift of 05 eV compared to the binding energy of Ti4+in P25 This suggests that Ti3+ was present in N-TiO
2and
the distance of peaks between Ti 2p12
and Ti 2p32
is 57ndash59 eV The 396 eV peak is assigned to the atomic b-N stateand generally proves the presence of TiAN bonds formedwhen N atoms replace the oxygen in the TiO
2crystal lattice
[30]The peak characteristic for TindashN (396 eV) is not presentindicating the absence of the TiN phase in the N-TiO
2
samples [34]The results show that the binding energies of Ti2p peaks shift to lower energieswith a negative shift ofsim05 eVfor the N-TiO
2due to the N doping [27] The lower binding
energy than a typical Ti 2p signal of Ti4+ oxidation state sug-gests that titanium cation has a considerable interaction withthe doped nitrogen and thus TiO
2lattice is modified [27
35] Nitrogen doping accompanies the formation of oxygenvacancies andor Ti3+ defects resulting in slight shifts of theTi 2p peak toward the lower binding energy [36ndash38] Hencethe red shifts of the Ti 2p peak in comparison with P25 areused to highlight the successful nitrogen doping into the TiO
2
lattice The XRD results did not indicate the formation ofTiN bondsTherefore results indicate that the titanium atombonds with oxygen but not nitrogen Thus a shift towardlower binding energy of Ti 2p and the binding energy of N1s upon nitrogen addition indicate that the nitrogen can beindeed incorporated into the interstitial positions of TiO
2
lattice and the formation of TindashOndashN bonding by partiallyinterstitial with a carbon atom
The incorporation of nitrogen into the oxide latticeshould influence the BE of O 1s as wellTheXPS spectra of theO 1s core level consists of the one peak (Figures 3(e) and 3(f))at around 5293ndash5295 eV which is ascribed to TindashO bondin the TiO
2lattice [30] The O 1s core level moved toward
lower energy state from 5296 eV in P25 to 5294 eV in N-TiO2prepared with AT ratio 30 and calcined at 400∘C The
peak shifts by sim02 eV which might be related to the creationof oxygen vacancies as a result of the nitrogen doping Theshifting of bind energy in both N 1s and O 1s region indicatesthat nitrogen was incorporated into the lattice The shifts ofTi 2p32
and O 1s peaks are due to the introduction of oxygenvacancies into the TiO
2lattice [32] The presence of nitrogen
dopant facilitates the formation of oxygen vacancies Theaforementioned results clearly indicate that nitrogen dopingis accompanied by oxygen vacancy formation The opticaltransitions between the dopant and dopant-induced level andTi3d orbital explain the observed visible light absorptions ofN-TiO
2nanomaterials The observed two absorbance edge
features in the UV-vis spectra are directly related to the abovemodification of the electronic states from the dopants
50
40
30
20
10
00 05 1 15 2 25 3
AmmoniaTTIP molar ratio
Rem
oval
effici
ency
()
Calcination temp
400∘C
500∘C
800∘C
Figure 8 The removal efficiency of ethylene photooxidation overN-TiO
2as function of the various ammoniaTTIP molar ratios
Experimental conditions [C2H4] = 200 ppmv [H
2O]= 25060 ppmv
[O2] = 21 light intensity = 16mWcm2 temp = 30∘C reaction time
= 3 h
36 Visible Light Photocatalytic Activity To explore the pho-tocatalytic activity of different N-doped TiO
2at different
calcination temperatures and AT ratios the degradationof ethylene under visible light with a cut-off wavelengthof 400 nm was investigated Carbon dioxide started beingformed immediately after the visible light was turned on andethylene was almost totally converted to CO
2in all mea-
surements It is obviously that the N-TiO2shows significant
progress in the photodegradation of ethylene compared toP25 in visible light system P25 has no obvious photocatalyticactivity (less than 1) under visible light irradiation Resultssuggest modification of TiO
2provides visible-light-sensitive
photocatalyst which can be applied to the photooxidationof ethylene gas as the band gap of TiO
2was modified by
nitrogen doping evidenced by XPS and UV-visible DRSresults Figure 8 shows the activity of N-TiO
2catalysts in the
presence of visible light for photodegradation of ethyleneThe reaction rate increases with the increase in the AT ratiofrom 05 to 20 and then decreases in AT ratio from 20to 30 The enhancement of photocatalytic activity can beascribed to an obvious improvement in anatase crystallinityand larger surface area For the sample prepared with ATratio 20 and 30 however the removal efficiency decreasedrapidly which can be due to its less surface area Thephotocatalytic ability of N-TiO
2samples calcinated at 400
500 and 800∘C is also examined It was found that thephotocatalytic activity decreased with increasing calcinationtemperature The enhancement of photocatalytic activitycan be ascribed to an obvious improvement in anatasecrystallinity at 400∘C calcination temperature Good anatasecrystallization is beneficial for reducing the recombinationrate of the photogenerated electrons and holes due to thedecrease in the number of the defects [39] Zhao and Yangshowed that for photocatalytic oxidation application anataseis superior to rutile (a) the conduction band location foranatase is more favorable for driving conjugate reactions
International Journal of Photoenergy 11
32 eVCO2 + H2O
IntermediatesH2O
OH∙ C2H4
eminuseminusTiIII OH
TiIV OH
TiIV OH
O2
∙O2minus
∙HOO H2O2
TiIV OH+∙
CB
VBh+ NS
OV
Figure 9 Schematic diagram for the process in the photooxidation of ethylene and electron transfer process over N-TiO2under visible light
illumination
involving electrons and (b) very stable surface peroxidegroups can be formed at the anatase during photo-oxidationreaction but not on the rutile surface [40] For the samplecalcined at 800∘C the removal efficiency decreased rapidlywhich can be due to its fewer amounts of anatase andsmall 119878BET The result indicates that higher specific surfacearea smaller crystallite size and good anatase crystallizationwill promote the photocatalytic activity in visible light Theresults indicate the N-TiO
2catalyst prepared with AT ratio
20 and calcinated at 400∘C shows the best photocatalyticability
37 The Formation Mechanism of N-Doped TiO2 For the
pure TiO2 the energy of the visible light is not sufficient
to excite electrons from the valence band (VB) as theintrinsic band gap of pure TiO
2 Based on the results of UV-
vis DRS XRD and XPS the nitrogen atoms were weavedinto the crystal structure of TiO
2with structure as TindashOndash
N N-TiO2was active in the visible light irradiation for
the degradation of ethylene The following explanation forthe photocatalytic activity of N-TiO
2in the visible light
spectra can be consideredThe nitrogen existing at interstitialpositions of TiO
2lattice induces localized occupied states and
forms midband gap leading to the red shift of absorptionedge and photocatalytic activity under visible light irradiation[41] The electron (eminus) can be excited from the N-impuritylevel to the conduction band (CB) The exited electrons aretrapped by O
2adsorbed on the catalyst surface producing
O2
minus∙ superoxide anion radicals After a series of reactions(1)ndash(12) ethylene molecules are finally mineralized into CO
2
DFT calcinations and experimental results indicate that N-doping favored the formation of O vacancy (subband levelO119907) which was below the bottom of the conduction band
[42ndash47] Therefore the electrons (eminus) are excited from theN-impurity level bond to the subband level (O
119907) and then
recombine with the hole (h+) as proved in Figure 9 Theholes and electrons react with OHminus and O
2molecules on the
catalyst surface to form ∙OH radicals and O2
minus∙ superoxideanion radicals respectivelyThe protonation yields theHOO∙radicals which after trapping electrons combine to produceH2O2 The O
2
minus∙ radicals then interact with H2O adsorbed to
produce more ∙OH radicals These ∙OH radicals then reactwith gaseous ethylene and mineralize it
TiO2
h120592997888997888997888997888997888rarr h+ + eminus (1)
SndashH2O + h+ 997888rarr SndashOH∙ +H+ (2)
SndashOHminus + h+ larrrarr SndashOH∙ (3)
S1015840ndashO2+ eminus 997888rarr S1015840ndashO
2
minus∙ (4)
SndashOH + S1015840ndashO2
minus∙997888rarr SndashHO
2
∙+ S1015840ndashOminus∙ (5)
S1015840ndashO2997888rarr 2S1015840ndashO (6)
S1015840ndashO + eminus 997888rarr S1015840ndashOminus∙ (7)
SndashH2O + S1015840ndashOminus∙ 997888rarr SndashOH∙ + SndashOHminus (8)
SndashHO2
∙+ SndashHO
2
∙997888rarr SndashH
2O2+O2
(9)
SndashH2O2997888rarr 2SndashOH∙ (10)
SndashC2H4+ SndashOH∙ larrrarr SndashC
2H4OH (11)
SndashC2H4OH + S1015840ndashO
2997888rarr intermediates 997888rarr CO
2+H2O(12)
4 Conclusions
The observed changes in the UV-vis DRS XRD and XPSspectra are providing consistent structural information forTindashOndashN formation that is the nitrogen can be incorporatedinto the interstitial positions of TiO
2lattice which leads to
the enhanced photocatalytic activity in N-TiO2samples It
is concluded that the photocatalytic oxidation reactivity ofN-TiO
2under visible light illumination is mainly due to the
presence of localized occupied states caused by interstitialnitrogen and the electronhole pairs generated under visiblelight irradiation It has been found that N dopant retardedthe anatase to rutile phase transformation by forming TindashOndashN incorporated into the interstitial position of TiO
2lattice
Moreover the transformation temperatures of anatase-to-rutile progressively slightly increase when N dopant contentis increased The photocatalyst N-TiO
2prepared with AT
ratio 20 and calcinated at 400∘C shows the highest photo-catalytic activity in the oxidation of ethylene This N-TiO
2
provides an effective visible-light-responsive photocatalystfor future industrial applications in pollution control
12 International Journal of Photoenergy
Acknowledgment
This research was financially supported by the NationalScience Council of Taiwan ROC under Grant nos NSC-100-2221-E-005-007 and NSC-100-2120-M-005-002
References
[1] T Horikawa M Katoh and T Tomida ldquoPreparation and char-acterization of nitrogen-doped mesoporous titania with highspecific surface areardquo Microporous and Mesoporous Materialsvol 110 no 2-3 pp 397ndash404 2008
[2] K Yang Y Dai and B Huang ldquoStudy of the nitrogen concen-tration influence onN-dopedTiO
2anatase fromfirst-principles
calculationsrdquo Journal of Physical Chemistry C vol 111 no 32 pp12086ndash12090 2007
[3] K Pomoni A Vomvas and C Trapalis ldquoDark conductivity andtransient photoconductivity of nanocrystalline undoped andN-doped TiO
2sol-gel thin filmsrdquoThin Solid Films vol 516 no 6
pp 1271ndash1278 2008[4] S Sato ldquoPhotocatalytic activity of NO
119909-doped TiO
2in the
visible light regionrdquo Chemical Physics Letters vol 123 no 1-2pp 126ndash128 1986
[5] R Asahi T Morikawa T Ohwaki K Aoki and Y TagaldquoVisible-light photocatalysis in nitrogen-doped titaniumoxidesrdquo Science vol 293 no 5528 pp 269ndash271 2001
[6] J Ananpattarachai P Kajitvichyanukul and S Seraphin ldquoVisi-ble light absorption ability and photocatalytic oxidation activityof various interstitial N-doped TiO
2prepared from different
nitrogen dopantsrdquo Journal of Hazardous Materials vol 168 no1 pp 253ndash261 2009
[7] Y T Lin C HWeng and TW Tzeng ldquoPhotocatalysis and cat-alytic properties of nano-sized N-TiO
2catalyst synthesized by
Sol-gel methodsrdquo Journal of Advanced Oxidation Technologiesvol 13 no 3 pp 297ndash304 2010
[8] B Kosowska S Mozia A W Morawski B Grzmil M Janusand K Kałucki ldquoThe preparation of TiO
2-nitrogen doped by
calcination of TiO2sdot xH2O under ammonia atmosphere for
visible light photocatalysisrdquo Solar Energy Materials and SolarCells vol 88 no 3 pp 269ndash280 2005
[9] F Peng L Cai L Huang H Yu and H Wang ldquoPreparationof nitrogen-doped titanium dioxide with visible-light photocat-alytic activity using a facile hydrothermal methodrdquo Journal ofPhysics and Chemistry of Solids vol 69 no 7 pp 1657ndash16642008
[10] H Yu X Zheng Z Yin F Tag B Fang and K HouldquoPreparation of nitrogen-doped TiO
2nanoparticle catalyst and
its catalytic activity under visible lightrdquo Chinese Journal ofChemical Engineering vol 15 no 6 pp 802ndash807 2007
[11] Z Wang W Cai X Hong X Zhao F Xu and C CaildquoPhotocatalytic degradation of phenol in aqueous nitrogen-doped TiO
2suspensions with various light sourcesrdquo Applied
Catalysis B vol 57 no 3 pp 223ndash231 2005[12] A Trenczek-Zajac K Kowalski K Zakrzewska and M
Radecka ldquoNitrogen-doped titanium dioxidemdashcharacterizationof structural and optical propertiesrdquoMaterials ResearchBulletinvol 44 no 7 pp 1547ndash1552 2009
[13] J S Jang H G Kim S M Ji et al ldquoFormation of crystallineTiO2minus119909
N119909and its photocatalytic activityrdquo Journal of Solid State
Chemistry vol 179 no 4 pp 1067ndash1075 2006[14] H L Qin G B Gu and S Liu ldquoPreparation of nitrogen-doped
titania using sol-gel technique and its photocatalytic activityrdquo
Materials Chemistry and Physics vol 112 no 2 pp 346ndash3522008
[15] J Xu Y Ao D Fu andC Yuan J ldquoLow-temperature preparationof anatase titania-coated magnetiterdquo Journal of Physics andChemistry of Solids vol 69 pp 1980ndash1984 2008
[16] DWuM LongW Cai C Chen and YWu ldquoLow temperaturehydrothermal synthesis of N-doped TiO
2photocatalyst with
high visible-light activityrdquo Journal of Alloys andCompounds vol502 no 2 pp 289ndash294 2010
[17] K M Parida and B Naik ldquoSynthesis of mesoporous TiO2minus119909
N119909
spheres by template free homogeneous co-precipitationmethodand their photo-catalytic activity under visible light illumina-tionrdquo Journal of Colloid and Interface Science vol 333 no 1 pp269ndash276 2009
[18] N R Neti R Misra P K Bera R Dhodapkar S Bakardjievaand Z Bastl ldquoSynthesis of c-doped TiO
2nanoparticles by no-
vel sol-gel polycondensation of resorcinol with formaldehydefor visible-light photocatalysisrdquo Synthesis and Reactivity inInorganic Metal-Organic and Nano-Metal Chemistry vol 40no 5 pp 328ndash332 2010
[19] K Bubacz J Choina D Dolat E Borowiak-Palen D Mos-zynski and A W Morawski ldquoStudies on nitrogen modifiedTiO2photocatalyst prepared in different conditionsrdquoMaterials
Research Bulletin vol 45 no 9 pp 1085ndash1091 2010[20] Z Zhang X Wang J Long Q Gu Z Ding and X Fu
ldquoNitrogen-doped titanium dioxide visible light photocatalystspectroscopic identification of photoactive centersrdquo Journal ofCatalysis vol 276 pp 201ndash214 2010
[21] X Z Bu G K Zhang Y Y Gao and Y Q Yang ldquoPrepara-tion and photocatalytic properties of visible light responsiveN-doped TiO
2rectorite compositesrdquo Microporous and Meso-
porous Materials vol 136 no 1ndash3 pp 132ndash137 2010[22] C Liu X Tang C Mo and Z Qiang ldquoCharacterization and
activity of visible-light-driven TiO2photocatalyst codopedwith
nitrogen and ceriumrdquo Journal of Solid State Chemistry vol 181no 4 pp 913ndash919 2008
[23] R Kun S Tarjan AOszko et al ldquoPreparation and characteriza-tion of mesoporous N-doped and sulfuric acid treated anataseTiO2catalysts and their photocatalytic activity under UV and
Vis illuminationrdquo Journal of Solid State Chemistry vol 182 pp3076ndash3084 2009
[24] Z Pap L Baia K Mogyorosi A Dombi A Oszko and VDanciu ldquoCorrelating the visible light photoactivity of N-dopedTiO2with brookite particle size and bridged-nitro surface
speciesrdquo Catalysis Communications vol 17 pp 1ndash7 2012[25] X Z Bu G K Zhang and CH Zhang ldquoEffect of nitrogen dop-
ing on anatase-rutile phase transformation of TiO2rdquo Applied
Surface Science vol 258 pp 7997ndash8001 2012[26] Y P Peng E Yassitepe Y T Yeh I Ruzybayev S I Shah and C
P Huang ldquoPhotoelectrochemical degradation of azo dye overpulsed laser deposited nitrogen-doped TiO
2thin filmrdquo Applied
Catalysis B vol 125 pp 465ndash472 2012[27] H Jie H B Lee K H Chae et al ldquoNitrogen-doped
TiO2nanopowders prepared by chemical vapor synthesis
band structure and photocatalytic activity under visible lightrdquoResearch on Chemical Intermediates vol 38 no 6 pp 1171ndash11802012
[28] S U M Khan M Al-Shahry and W B Ingler ldquoEfficientphotochemical water splitting by a chemically modified n-TiO2rdquo Science vol 297 no 5590 pp 2243ndash2245 2002
International Journal of Photoenergy 13
[29] X X Wang S Meng X L Zhang H T Wang W Zhong andQ G Du ldquoMulti-type carbon doping of TiO
2photocatalystrdquo
Chemical Physics Letters vol 444 pp 292ndash296 2007[30] N R Khalid E Ahmed Z L Hong Y W Zhang and
M Ahmad ldquoNitrogen doped TiO2nanoparticles decorated
on graphene sheets for photocatalysis applicationsrdquo CurrentApplied Physics vol 12 no 6 pp 1485ndash1492 2012
[31] Q J Xiang J G Yu and M Jaroniec ldquoNitrogen and sulfurco-doped TiO
2nanosheets with exposed 001 facets synthesis
characterization and visible-light photocatalytic activityrdquo Phys-ical Chemistry Chemical Physics vol 13 no 11 pp 4853ndash48612011
[32] J Wang D N Tafen J P Lewis et al ldquoOrigin of photocatalyticactivity of nitrogen-doped TiO
2nanobeltsrdquo Journal of the
American Chemical Society vol 131 pp 12290ndash12297 2009[33] Q Xiang J YuWWang andM Jaroniec ldquoNitrogen self-doped
nanosized TiO2sheets with exposed 001 facets for enhanced
visible-light photocatalytic activityrdquoChemical Communicationsvol 47 no 24 pp 6906ndash6908 2011
[34] Y C Tang X H Huang H Q Yu and L H Tang ldquoNitrogen-doped TiO
2photocatalyst prepared by mechanochemical
method doping mechanisms and visible photoactivity of pol-lutant degradationrdquo International Journal of Photoenergy vol2012 Article ID 960726 10 pages 2012
[35] D E Gu Y Lu B C Yang and Y D Hu ldquoFacile preparationof micro-mesoporous carbon-doped TiO
2photocatalysts with
anatase crystalline walls under template-free conditionrdquo Chem-ical Communications no 21 pp 2453ndash2455 2008
[36] W Ren Z Ai F Jia L Zhang X Fan and Z Zou ldquoLow tem-perature preparation and visible light photocatalytic activity ofmesoporous carbon-doped crystalline TiO
2rdquo Applied Catalysis
B vol 69 no 3-4 pp 138ndash144 2007[37] EM Rockafellow X Fang B G Trewyn K Schmidt-Rohr and
W S Jenks ldquoSolid-state 13C NMR characterization of carbon-modified TiO
2rdquo Chemistry of Materials vol 21 no 7 pp 1187ndash
1197 2009[38] Y Zhang P Xiao X Zhou D Liu B B Garcia and G Cao
ldquoCarbon monoxide annealed TiO2nanotube array electrodes
for efficient biosensor applicationsrdquo Journal of Materials Chem-istry vol 19 no 7 pp 948ndash953 2009
[39] J Yu L Zhang B Cheng andY Su ldquoHydrothermal preparationand photocatalytic activity of hierarchically sponge-like macro-mesoporous Titaniardquo Journal of Physical Chemistry C vol 111no 28 pp 10582ndash10589 2007
[40] J Zhao and X Yang ldquoPhotocatalytic oxidation for indoor airpurification a literature reviewrdquo Building and Environment vol38 no 5 pp 645ndash654 2003
[41] C Di Valentin G Pacchioni and A Selloni ldquoOrigin of thedifferent photoactivity of N-doped anatase and rutile TiO
2rdquo
Physical ReviewB vol 70 no 8 Article ID 085116 4 pages 2004[42] S Livraghi M C Paganini E Giamello A Selloni C
Di Valentin and G Pacchioni ldquoOrigin of photoactivity ofnitrogen-doped titanium dioxide under visible lightrdquo Journal ofthe American Chemical Society vol 128 no 49 pp 15666ndash156712006
[43] X Chen and C Burda ldquoThe electronic origin of the visible-lightabsorption properties of C- N- and S-doped TiO
2nanomateri-
alsrdquo Journal of the American Chemical Society vol 130 no 15pp 5018ndash5019 2008
[44] C Di Valentin G Pacchioni and A Selloni ldquoTheory of carbondoping of titanium dioxiderdquo Chemistry of Materials vol 17 no26 pp 6656ndash6665 2005
[45] HWang and J P Lewis ldquoEffects of dopant states on photoactiv-ity in carbon-dopedTiO
2rdquo Journal of Physics CondensedMatter
vol 17 no 21 pp L209ndashL213 2005[46] H Li D Wang H Fan P Wang T Jiang and T Xie ldquoSynthesis
of highly efficient C-doped TiO2photocatalyst and its photo-
generated charge-transfer propertiesrdquo Journal of Colloid andInterface Science vol 354 no 1 pp 175ndash180 2011
[47] ZWu FDongWZhao and SGuo ldquoVisible light induced elec-tron transfer process over nitrogen doped TiO
2nanocrystals
prepared by oxidation of titaniumnitriderdquo Journal of HazardousMaterials vol 157 no 1 pp 57ndash63 2008
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
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Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
International Journal of Photoenergy 3
Elite-Plot-Q capillary column (Agilent Technologies) Theethylene was allowed to reach adsorption equilibrium withthe catalyst in the reactor prior to irradiation Two 500-W horizontal halogen lamps (95 cm in length PHILIPS)were used to simulate the solar light The lamp equippedwith a cut-off filter (120582 gt 400 nm) was vertically placedoutside the photocatalytic reactor Light intensity at thecatalyst surface was 16mWcm2 Blank experiments usingan uncoated (no catalyst) glass plate had no effect on theethylene concentration and did not generate any carbonmonoxide or carbon dioxide (see supplementary materialonline at httpdxdoiorg1011552013268723) The photo-catalytic activity of the catalyst can be quantitatively evaluatedby comparing the apparent reaction rate constants
3 Results and Discussion
31 Thermal Analysis To investigate the process of phasetransformation of titanium(IV)-oxide-hydroxide to titaniumoxide and the effect of nitrogen doping content on thetransformation from anatase to rutile thermoanalytic tech-niques including TGA and DTA were conducted Typicallythe hydrothermal weight loss is attributed to a multistepof polycondensation of titanium(IV)-oxide-hydroxide andphase transformation of anatase into rutile or brookite fromroom temperature to 700ndash800∘C as shown in Figure 1 andTable 1 DTA measurements established the transformationof TiO
119909(OH)119910into TiO
2including two endothermic and
one exothermic peaks from room temperature to 398∘C(Figure 1) A sharp endothermic peaks at 105∘C due to therelease of absorbed water while the other minor peak at253∘C is referred to as the desorption of organic Therewas a corresponding weight loss from TGA of about 198and 94wt respectively In the region mentioned abovethe finely exothermic peak around 276∘C is ascribed to thethermal decomposition of unhydrolyzed TTIP with about08 wt weight loss The weak thermal effect at 276ndash730∘Cis accompanied by obvious exothermic peak at 451∘C whichcan be assigned to the crystallization of the amorphous phaseto anatase At around 730∘C an obvious exothermic peakwas observed owing to the oxidation of carbon residue andevaporation of chemisorbed water which can be assignedto the phase transformation from anatase titania to rutileTiO2 It can be concluded from the DTA result that the as-
prepared TiO2sample was amorphous According to TGA
the weight loss roughly consists of three distinct stages Thefirst stage was up to 276∘C over which the mass loss is thegreatest A mass loss of up to 30 was observed which isattributed to the evaporation of the physical adsorbed waterand the release of organic The second stage is from 276 to451∘C where the mass loss is about 17This corresponds tothe thermal decomposition of unhydrolyzed TTIP The thirdstage is from 451 to 730∘C and the mass loss is about 07which is attributed to the removal of chemisorbed water Atabout 730∘C no mass loss was observed The exothermicpeaks of N-TiO
2prepared at 05 10 and 20 AT ratios
were at 710 720 and 730∘C respectively (Table 1)The resultsindicated that nitrogen atoms doped in TiO
2could prevent
100
80
60
40
20
0
60
50
40
30
20
10
00 100 200 300 400 500 600 700 800
Wei
ght l
oss (
)
Hea
t flow
(mW
mg)
Temperature (∘C)
198 94 17 07
105∘ C
253∘ C
276∘ C
451∘ C
730
∘ C
Anatase into rutile
Release of adsorbed water
Desorption of organics
Amorphous into anatase
Thermal decomposition of unhydrolyzed TTIP
Figure 1 TG-DTA curve of N-TiO2samples prepared with 20
ammoniaTTIP ratio
phase transition of anatase to rutile because as far as pureTiO2was concerned most TiO
2particles were transformed
into rutile at 700∘C
32 Phase and Structure The characteristics of N-TiO2at
various calcination temperatures and molar ratios of ATare summarized in Table 1 Figure 2 shows the XRD patternof the N-TiO
2samples at various AT ratios and annealed
at different temperatures The presence of peaks (2120579 =2544∘ 3806
∘ and 4824∘) was regarded as an attributive
indicator of anatase titania and the presence of peaks (2120579 =2754∘ 3614
∘ and 4120∘) was regarded as an attributive
indicator of rutile titaniaThediffraction peaks for the anatase(JCPDSno 21-1272) and rutile (JCPDSno 21-1276) phases aremarked with ldquoArdquo and ldquoRrdquo respectively and the correspondingdiffraction planes are given in parenthesis No N-derivedpeaks were detected in all the patternsThismay be caused bythe lower concentration of the doped species and the limiteddopants may have moved into either the interstitial positionsor the substitutional sites of the TiO
2crystal structure which
is consistent with [8 9] The average grain size was estimatedat 28ndash131 nm comparable to that from the HRTEM imageA comparison of XRD patterns clearly shows that nitrogendoping significantly changes the crystalline size and thecrystal structure of TiO
2
The transformation from the amorphous to the crys-talline form of TiO
2usually requires temperatures close
to 300∘C [8] For the samples prepared with 20 AT andcalcinated at 400ndash500∘C (Figure 2(a)) the intensities ofthe anatase peak are increased and the width of the (101)plane diffraction peak becomes narrower as the calcinationtemperature increases implying an improvement and growthin crystallinity Increasing the temperature to 800∘C theintensity of anatase peak decreases but the rutile peaksappear suggesting the transformation of anatase to rutilephase The average crystalline size was 32 85 and 103 nmand the mass percentage of anatase was 90 60 and 6 forsamples prepared at 20 AT and calcination temperature
4 International Journal of Photoenergy
Table 1 Characteristics for N-TiO2 at various ammoniaTTIP molar ratios under different calcination temperatures
SampleaXRD BET TG-DTA TEM Optical properties
Phase ratio Crystallite size Surface area (m2g) Abrarr Rc Temp (∘C) Size (nm) 1205821198921 1198641198921 1205821198922 1198641198922
Ab Rc Ab (nm) Rc (nm) (nm) (nm) (nm) (nm)A00T4 90 10 32 mdash 93 703 11 plusmn 1 392 316 mdash mdashA05T4 89 11 28 mdash 108 710 12 plusmn 1 392 316 505 246A10T4 90 10 28 mdash 119 720 12 plusmn 1 391 317 506 245A15T4 87 13 29 mdash 119 728 11 plusmn 1 388 320 513 242A20T4 90 10 32 mdash 98 730 12 plusmn 1 390 318 510 243A25T4 90 10 37 mdash 98 728 12 plusmn 1 392 316 515 241A30T4 92 8 37 mdash 86 729 12 plusmn 1 392 316 514 241A00T5 94 6 46 mdash 50 703 13 plusmn 2 402 308 mdash mdashA05T5 89 11 46 98 64 710 13 plusmn 1 404 307 503 247A10T5 90 10 41 87 68 720 15 plusmn 2 400 310 508 244A15T5 91 9 40 mdash 71 728 15 plusmn 2 396 313 517 240A20T5 94 6 45 mdash 62 730 15 plusmn 2 394 315 513 242A25T5 94 6 49 mdash 55 728 17 plusmn 2 397 312 507 245A30T5 94 6 47 mdash 53 729 17 plusmn 2 397 312 510 243A00T6 34 66 106 156 7 703 24 plusmn 2 420 295 mdash mdashA05T6 14 86 86 128 8 710 40 plusmn 3 422 294 mdash mdashA10T6 14 86 81 132 9 720 40 plusmn 4 425 292 mdash mdashA15T6 22 78 79 141 14 728 35 plusmn 3 424 292 mdash mdashA20T6 60 40 85 184 17 730 34 plusmn 3 415 299 mdash mdashA25T6 78 22 90 184 16 728 35 plusmn 4 416 298 mdash mdashA30T6 74 26 97 169 12 729 36 plusmn 4 415 299 mdash mdashA00T7 6 94 131 177 2 703 80 plusmn 5 424 292 mdash mdashA05T7 3 97 95 148 5 710 145 plusmn 10 428 290 mdash mdashA10T7 3 97 102 149 6 720 145 plusmn 10 429 289 mdash mdashA15T7 3 97 92 159 6 728 150 plusmn 11 428 290 mdash mdashA20T7 6 94 103 163 4 730 170 plusmn 13 428 290 mdash mdashA25T7 15 85 108 178 8 728 60 plusmn 6 426 291 mdash mdashA30T7 15 85 117 182 6 729 60 plusmn 6 427 290 mdash mdashA00T8 1 99 mdash 174 3 703 200 plusmn 17 424 292 mdash mdashA05T8 1 99 mdash 161 3 710 190 plusmn 15 428 290 mdash mdashA10T8 1 99 mdash 159 3 720 160 plusmn 13 429 289 mdash mdashA15T8 1 99 mdash 171 3 728 170 plusmn 15 428 290 mdash mdashA20T8 1 99 mdash 164 2 730 160 plusmn 14 428 290 mdash mdashA25T8 3 97 106 184 4 728 200 plusmn 18 427 290 mdash mdashA30T8 3 97 127 179 3 729 170 plusmn 15 429 289 mdash mdashaAXXTY ammoniaTTIP molar ratio = 0XX calcination temperature = Y00∘CbAnatasecRutile
of 400 600 and 700∘C respectively The maximum meansize of anatase and rutile crystallites was observed at 800∘CResults agreed with those reported that the crystalline sizegrows and the content of anatase diminishes as calcinationtemperature increases [8 10ndash13] For the samples prepared at05 AT the anatase peaks appear at temperatures 400 and500∘C Increasing the temperature to 500∘C the intensity ofanatase peak decreases but the rutile peaks appear Whentemperature is increased further to 600∘C rutile becomesa main phase In this case the anatase-to-rutile phasetransformation temperature is between 400 and 500∘C XRD
patterns of samples prepared at 30 AT and annealed at700∘C show both anatase and a rutile phase indicating thatanatase-to-rutile phase transformation is shifted to highertemperature It can be seen that the presence of nitrogencan restrain the formation and growth of TiO
2crystal phase
thereby retarding the anatase-to-rutile phase transformationThis result is further supported by the appearance of rutilein XRD patterns of sample prepared at 05 and 15 GTat 600∘C and disappearance for samples prepared at GTgreater than 20 at 600∘C (data not shown) Comparedwith P25 the peak position of the (101) plane of N-doped
International Journal of Photoenergy 5
A A A
A A
AR
R
RR R R
(101) (110) (004) (204)(200)
(105)(211)
(101)
(111)
(210) (211) (220)
Inte
nsity
(au
)
20 30 40 50 60 70 80
Calcination temperature (∘C)400
500
600
700
800
2120579 (deg)
AT ratio 2
(a)
A A A A A A(101) (004) (204)(200)(105)(211)
Inte
nsity
(au
)
20 30 40 50 60 70 80
0051
15
2253
2120579 (deg)
AT ratio
Calcination temperature 400∘C
P25
(b)
Figure 2 XRD patterns of N-TiO2samples prepared (a) at various calcination temperatures and (b) with various ammoniaTTIP ratios
TiO2shifted slightly to higher 2120579 value and the peak was
broader as NT ratio increases suggesting distortion of thecrystal lattice of TiO
2by the incorporation of nitrogen The
crystalline sizes of samples calcinated at 400∘C and pre-pared at 05 15 20 and 30 AT were 28 29 32 and37 nm respectively The average crystalline size of samplesincreases with increase in AT revealing that nitrogen canenhance the growth of N-TiO
2crystals Results agreed with
those reported that the crystalline size grows as nitrogento Ti proportion increases [14] The results reveal that thephase transformation temperature of anatase to rutile wasprogressively increased when the amount of N dopant wasincreased Clearly calcination temperature andAT ratio playa significant role in the formed crystal structure and particlesize (Figure 3)Higher temperature favors the growth of rutilestructure and produces N-TiO
2nanoparticles with larger
particle size Thus a fine control of calcination temperatureand AT ratio is crucial for obtaining a pure phase of N-TiO
2
Further insights into the effect of calcination and dopingon the morphology and structure of the N-TiO
2samples can
be obtained from HRTEM image (Figure 4) The selectedarea electron diffraction pattern and TEM confirmed itshighly crystalline anatase or rutile structure The observedd-spacing from HRTEM image is 3522 A and is comparableto 352 A previously reported for (101) crystallographic planeof undoped anatase [15ndash18] The HRTEM image showedthe nanocrystallines with primary grain size around 11ndash200 nm From the TEM images the particles in N-TiO
2
samples are monodispersed The crystalline form aggregateswith a mesoporous structure The formation of mesoporousstructure is similar to that reported in the literature [1920] First monodispersed amorphous titanium oxide solparticles are formed by the hydrolysis processes Then themonodispersed sol particles are crystallized and aggregatedunder calcination treatment to form mesoporous crystallineBased on the HRTEM results the calcination temperature
100
80
60
40
20
0400 500 600 700 800Calcination temperature (∘C)
AmmoniaTTIP molar ratio
Ana
tase
()
005115
2253
Figure 3 The anatase content of N-TiO2samples as a function of
the various ammoniaTTIP molar ratios
significantly changes the size of particles (Table 1) The grainsize of crystalline is in consistent with the calculated valueobtained from XRD patterns (Table 1) The grain size ofsamples increases with the calcination temperatureMorpho-logical observation by TEM and XRD calculations revealsthat the large particle size of A20T8 was mainly caused byagglomeration and the growth of crystallite size
33 Surface Area and Pore Size Distribution Typical nitrogenadsorption-desorption isotherms of N-TiO
2photocatalyst
6 International Journal of Photoenergy
400∘C
10nm
(a)
500∘C
10nm
(b)
600∘C
50nm
(c)
700∘C
50nm
(d)
100nm
800∘C
(e) (f)
Figure 4 TEM images of N-TiO2prepared (a)ndash(e) at various calcination temperatures with 20 ammoniaTTIP ratio and (f) the selected
area electron diffraction of A20T4
are shown in Figure 5 The 119878BET of N-TiO2prepared with 20
AT ratio at calcined 400 500 600 700 and 800∘C was 9862 17 4 and 2m2g respectively Obviously the values of119878BET and pore volume of N-TiO
2prepared with the same AT
ratio decreased with increasing calcination temperaturesSuch phenomenon could be attributed to the collapse of themesoporous structure the growth of TiO
2crystallites and
the removal process of nitrogen core by high-temperaturecalcination Consequently N-TiO
2calcined at 800∘C has the
least 119878BET Based on the results obtained the hysteresis loop ofN-TiO
2is significantly shifted in direction of higher relative
pressures as calcination temperature increases indicatingmuch larger mesorpore The average pore size of N-TiO
2
increased with increasing calcination temperature due to theformation of slit-like pores [21]
The N-TiO2samples obtained at various calcination
temperatures gave different nitrogen adsorption isotherms(Figure 5) implying differences in their porous structureThe N-TiO
2samples prepared at low calcination temperature
(ie 400 and 500∘C) exhibited a type IV isotherm and atype H2 hysteresis loop at lower relative pressure regionwhich are typical characteristics of mesoporous structurewith ink bottle pores Note that the adsorption branches ofthese isotherms resembled type II indicating the presence ofsome macropores Otherwise the N-TiO
2samples prepared
at higher calcination temperature (ie 600ndash800∘C) exhibiteda type V isotherm and a type H3 hysteresis loop at higherrelative pressureThe hysteresis loop at lower relative pressureregion (04 lt 119875119875
0lt 08) was attributed to a smaller mes-
opore while that at the higher relative pressure (08 lt1198751198750lt 10) was of larger mesopores Thus samples prepared
at high calcination temperature (gt600∘C) had a wide poresize distribution in the mesopores scale The isotherm of N-TiO2prepared at higher calcination temperature was below
that of lower calcination temperature (Figure 5) indicatinglower surface area and pore volume of the former Furtherobservation from Table 1 indicated that 119878BET for the N-TiO
2
samples at the same AT ratio increased with increasingcalcination temperature (Figure 5(c)) Results reveal thatall N-TiO
2samples calcined at various temperatures show
monomodal pore size distributions and mesopores may beassigned to the pores among interaggregated particles (datanot shown) With calcination temperature increasing thereis a significant tendency of pore size distribution toward tothe bigger pore size The increase of pore size is due to thecorruption of smaller pores during calcination as the smallerpores endured much greater stress than the bigger poresFormation of bigger crystalline aggregation upon increasein temperature could form bigger pores also Consequentlythe pore size increases while the pore volume decreases with
International Journal of Photoenergy 7
200
150
100
50
00 02 04 06 08 1
400500600
700800
IV
IV
V
VV
AmmoniaTTIP ratio 2Calcination temperature (∘C)
Qua
ntity
adso
rbed
(cm
3g
STP
)
Relative pressure (1198751198750)
(a)
0 02 04 06 08 1
005115
2253
IV
250
200
150
100
50
0
H3
Calcination temperature 400∘CAmmoniaTTIP ratio
Qua
ntity
adso
rbed
(cm
3g
STP
)
Relative pressure (1198751198750)
(b)
0
120
100
80
60
40
20
0400 500 600 700 800
Calcination temperature (∘C)
Surfa
ce ar
ea (m
2g
)
05115
2253
AmmoniaTTIP ratio
(c)
Figure 5 Nitrogen adsorption and desorption isotherms of N-TiO2samples (a) calcined at various temperatures (b) prepared with various
ammoniaTTIP molar ratios the surface area as a function of calcination temperature
calcinations temperature increasing Based on the TEM andBET results the mesopores of TiO
2were decreased due
to the heat shrinkage of calcination The results indicatedthat calcination at high temperature and in the presence ofnitrogen atoms will help to improve the thermal stabilityof the photocatalyst While the calcination temperature wasincreased both the specific surface area and the pore vol-ume of N-TiO
2samples decreased This indicated that the
average pore size increased while the pore volume and the
specific surface area decreased with calcination temperatureincreasing
34 Optical Properties The typical UV-vis diffuse reflectancespectra of N-TiO
2are shown in Figures 6(a) and 6(b) It can
be seen that nondoped TiO2(P25) has only one light sharp
edge (120582 = 410 nm) which can be assigned to the band gapof TiO
2 while part of N-TiO
2showed two absorption edges
and a noticeable shift to the visible light region as compared
8 International Journal of Photoenergy
400500600
700800
2
15
1
05
0
Abso
rban
ce (a
u)
Abso
rban
ce (a
u)
200 300 400 500 600 700 800Wavelength (nm)
Wavelength (nm)Calcination temp (∘C)
05
04
03
02
01
0350 400 450 500 550
NTi 2 molar ratiocalcination at different temperatures
AT ratio 2
A20T4A20T5A20T6A20T7A20T8
P25
(a)
2
15
1
05
0
Abso
rban
ce (a
u)
200 300 400 500 600 700 800Wavelength (nm)
Abso
rban
ce (a
u)
Wavelength (nm)
04
04
03
03
02
02
01
01380 400 420 440 460 480 500 520 540
Calcination at 400∘C temperaturedifferent NTi molar ratios
325
215
1050P25
A00T4A05T4A10T4A15T4
A20T4A25T4A30T4
AT ratio
Calcination temperature 400∘C
(b)
Figure 6 The typical UV-vis DR spectra of N-TiO2samples (a) prepared with 20 ammoniaTTIP molar ratio and calcined at various
temperatures (b) prepared with various ammoniaTTIP molar ratios and calcined at 400∘C
to that of the TiO2(ie P25) This phenomenon should be
ascribed to either the nitrogen doping andor sensitizationby a surface-anchored group The calcination temperatureand AT ratio are the crucial factor that can further affectthe absorption as seen in Figure 6 Similar phenomenonhad been reported by previous publications [17 22ndash25] Theabsorption edges of the N-TiO
2samples show continuous
red shift as the calcination temperature changes from 400to 700∘C which can be assigned to the intrinsic band gapabsorption of TiO
2 The shift is too minor to be observed
when the calcination temperature changes from500 to 600∘Cwhich is possibly caused by the synergetic effect of the loss ofthe nitrogen and the increase of the TiO
2crystallinity during
the calcination processThe absorption threshold (120582119892) can be
determined using the onset of the absorption edges by thesection of the fitting lines on the upward and outward sectionof the spectrum (shown in the graph inserted in Figure 6)[23] Table 1 lists the determined 120582
119892(nm) and the derived
band gap energy values The band gap of N-TiO2(119864119892) was
calculated using the 119864119892= 1240120582
119892equation It also can be
seen that N-TiO2samples have two characteristic light
absorption edges One of them corresponds to the band gapof TiO
2(1205821198921= 390sim430 nm) while the other originates from
the N-induced midgap level (1205821198922= 505sim517 nm) The color
of the samples was different with calcination temperatureand AT ratio The color of N-TiO
2samples prepared with
20 AT ratio and calcinated at 400 600 and 700∘C wasvivid yellow yellow and white respectively There is no 120582
1198922
when N-TiO2calcinated above 600∘C It can be ascribed to
the amount of N dopant decreased The color of N-TiO2
prepared with 00 10 20 and 30 AT ratio and calcinatedat 400∘C was white pale yellow yellow and vivid yellow
respectively The phenomenon that the AT ratio increasesthe shifting of the spectra towards visible region was clearlyobserved (Figure 6(a)) The absorption threshold (120582
119892) was
increased with increasing AT ratio It reveals that morenitrogen doping in the matrix of TiO
2structure results in a
shift of absorbance region toward visible light wavelengthThis is possible attribute to the nitrogen incorporated intoTiO2lattice and formation of new electronic state above
valence band caused by nitrogen doping to generate a redshift
35 Analysis of Chemical State The chemical states of dopingimpurity are critical to the optical property band gap andphotocatalytic activity of nitrogen-dopedTiO
2 To investigate
the chemical states of the doping nitrogen XPS spectra wereapplied to examine three regions the Ti 2p core level near460 eV the O 1s core level near 530 eV and the N 1s core levelnear 400 eV Figure 7 shows the experimental observation ofsurface chemical composition and the electronic structuresof N-TiO
2samples using XPS XPS peaks showed that the N-
TiO2contained only Ti O N elements and a small quantity of
carbon The presence of carbon was ascribed to the residualcarbon from the precursor solution and the adventitioushydrocarbon from the XPS instrument itself In Figures 7(a)and 7(b) the binding energy (BE) peaks corresponding toN 1s core levels for N-TiO
2are observed one major peak at
400 eV The N 1s peak at 400 eV is ascribed to the presenceof the oxidized nitrogen species and the nitrogen may beincorporating into the interstitial positions of the TiO
2lattice
and to form a TindashOndashN structure [26 27] No other N 1s peakswere detected in N-TiO
2samples As shown in Figure 7 N 1s
peak at 400 eV slightly decreased with increasing calcination
International Journal of Photoenergy 9
Bind energy (eV)
Inte
nsity
(au
)800
700
600
500
400
Calcination temp (∘C)Ti-O-N
390 395 400 405 410
AT ratio 2
(a)
Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
325
2
15
1
05
0
Ti-O-N
390 395 400 405 410
AT ratio
(b)
Bind energy (eV)
Inte
nsity
(au
) 800
700
600
500
400
Calcination temp (∘C)
Ti-O
524 526 528 530 532 534 536
AT ratio 2
(c)
Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
3
25
2
15
1
05
0
Ti-O
524 526 528 530 532 534 536
AT ratio
(d)
454 456 458 460 462 464 466 468Bind energy (eV)
Inte
nsity
(au
)
4582
4581
4583
458
4583
800
700
600
500
400
Calcination temp (∘C)AT ratio 2Ti4+2p32
Ti4+2p12
(e)
454 456 458 460 462 464 466 468Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
3
25
2
15
1
05
0
Ti4+2p32
Ti4+2p12 AT ratio
(f)
Figure 7 XPS survey and core level spectra of (a)-(b) N 1s (c)-(d) Ti 2p and (e)-(f) O 1s of N-TiO2samples
temperature This is different from the N-TiO2prepared by
flame oxidation in which nitrogen partially substitutes theoxygen sites in the TiO
2[28] The preparation method plays
an important role in determining the nitrogen state in TiO2
band structure [26 29 30]Depending on the nitrogen source
and experimental conditions N species are incorporated intoTiO2in interstitial form or substitutional form [31 32] The
interstitial N-doping is favored when the doping is carriedout under oxygen-rich conditions and the substation-typeN-doping occurs under reducing conditions [31ndash33] Therefore
10 International Journal of Photoenergy
from the atomicN 1sXPS spectra the interstitial sites (400 eV)were observed under air atmosphere
The XPS spectra of Ti 2p regions are shown in Figures7(c) and 7(d) The peaks at around 4585 and 4642 eV forP25 are ascribed to Ti 2p
32and Ti 2p
12of TiO
2(data not
shown)The line separation between Ti 2p12
and Ti 2p32
was57 eV which is consistent with the standard binding energyAccording to Figure 7 all spectra of Ti 2p
12are symmetry
The spectra of Ti 2p12
are consistent of single state and thebanding energy of peaks is 4580ndash4583 eV which shows aredshift of 05 eV compared to the binding energy of Ti4+in P25 This suggests that Ti3+ was present in N-TiO
2and
the distance of peaks between Ti 2p12
and Ti 2p32
is 57ndash59 eV The 396 eV peak is assigned to the atomic b-N stateand generally proves the presence of TiAN bonds formedwhen N atoms replace the oxygen in the TiO
2crystal lattice
[30]The peak characteristic for TindashN (396 eV) is not presentindicating the absence of the TiN phase in the N-TiO
2
samples [34]The results show that the binding energies of Ti2p peaks shift to lower energieswith a negative shift ofsim05 eVfor the N-TiO
2due to the N doping [27] The lower binding
energy than a typical Ti 2p signal of Ti4+ oxidation state sug-gests that titanium cation has a considerable interaction withthe doped nitrogen and thus TiO
2lattice is modified [27
35] Nitrogen doping accompanies the formation of oxygenvacancies andor Ti3+ defects resulting in slight shifts of theTi 2p peak toward the lower binding energy [36ndash38] Hencethe red shifts of the Ti 2p peak in comparison with P25 areused to highlight the successful nitrogen doping into the TiO
2
lattice The XRD results did not indicate the formation ofTiN bondsTherefore results indicate that the titanium atombonds with oxygen but not nitrogen Thus a shift towardlower binding energy of Ti 2p and the binding energy of N1s upon nitrogen addition indicate that the nitrogen can beindeed incorporated into the interstitial positions of TiO
2
lattice and the formation of TindashOndashN bonding by partiallyinterstitial with a carbon atom
The incorporation of nitrogen into the oxide latticeshould influence the BE of O 1s as wellTheXPS spectra of theO 1s core level consists of the one peak (Figures 3(e) and 3(f))at around 5293ndash5295 eV which is ascribed to TindashO bondin the TiO
2lattice [30] The O 1s core level moved toward
lower energy state from 5296 eV in P25 to 5294 eV in N-TiO2prepared with AT ratio 30 and calcined at 400∘C The
peak shifts by sim02 eV which might be related to the creationof oxygen vacancies as a result of the nitrogen doping Theshifting of bind energy in both N 1s and O 1s region indicatesthat nitrogen was incorporated into the lattice The shifts ofTi 2p32
and O 1s peaks are due to the introduction of oxygenvacancies into the TiO
2lattice [32] The presence of nitrogen
dopant facilitates the formation of oxygen vacancies Theaforementioned results clearly indicate that nitrogen dopingis accompanied by oxygen vacancy formation The opticaltransitions between the dopant and dopant-induced level andTi3d orbital explain the observed visible light absorptions ofN-TiO
2nanomaterials The observed two absorbance edge
features in the UV-vis spectra are directly related to the abovemodification of the electronic states from the dopants
50
40
30
20
10
00 05 1 15 2 25 3
AmmoniaTTIP molar ratio
Rem
oval
effici
ency
()
Calcination temp
400∘C
500∘C
800∘C
Figure 8 The removal efficiency of ethylene photooxidation overN-TiO
2as function of the various ammoniaTTIP molar ratios
Experimental conditions [C2H4] = 200 ppmv [H
2O]= 25060 ppmv
[O2] = 21 light intensity = 16mWcm2 temp = 30∘C reaction time
= 3 h
36 Visible Light Photocatalytic Activity To explore the pho-tocatalytic activity of different N-doped TiO
2at different
calcination temperatures and AT ratios the degradationof ethylene under visible light with a cut-off wavelengthof 400 nm was investigated Carbon dioxide started beingformed immediately after the visible light was turned on andethylene was almost totally converted to CO
2in all mea-
surements It is obviously that the N-TiO2shows significant
progress in the photodegradation of ethylene compared toP25 in visible light system P25 has no obvious photocatalyticactivity (less than 1) under visible light irradiation Resultssuggest modification of TiO
2provides visible-light-sensitive
photocatalyst which can be applied to the photooxidationof ethylene gas as the band gap of TiO
2was modified by
nitrogen doping evidenced by XPS and UV-visible DRSresults Figure 8 shows the activity of N-TiO
2catalysts in the
presence of visible light for photodegradation of ethyleneThe reaction rate increases with the increase in the AT ratiofrom 05 to 20 and then decreases in AT ratio from 20to 30 The enhancement of photocatalytic activity can beascribed to an obvious improvement in anatase crystallinityand larger surface area For the sample prepared with ATratio 20 and 30 however the removal efficiency decreasedrapidly which can be due to its less surface area Thephotocatalytic ability of N-TiO
2samples calcinated at 400
500 and 800∘C is also examined It was found that thephotocatalytic activity decreased with increasing calcinationtemperature The enhancement of photocatalytic activitycan be ascribed to an obvious improvement in anatasecrystallinity at 400∘C calcination temperature Good anatasecrystallization is beneficial for reducing the recombinationrate of the photogenerated electrons and holes due to thedecrease in the number of the defects [39] Zhao and Yangshowed that for photocatalytic oxidation application anataseis superior to rutile (a) the conduction band location foranatase is more favorable for driving conjugate reactions
International Journal of Photoenergy 11
32 eVCO2 + H2O
IntermediatesH2O
OH∙ C2H4
eminuseminusTiIII OH
TiIV OH
TiIV OH
O2
∙O2minus
∙HOO H2O2
TiIV OH+∙
CB
VBh+ NS
OV
Figure 9 Schematic diagram for the process in the photooxidation of ethylene and electron transfer process over N-TiO2under visible light
illumination
involving electrons and (b) very stable surface peroxidegroups can be formed at the anatase during photo-oxidationreaction but not on the rutile surface [40] For the samplecalcined at 800∘C the removal efficiency decreased rapidlywhich can be due to its fewer amounts of anatase andsmall 119878BET The result indicates that higher specific surfacearea smaller crystallite size and good anatase crystallizationwill promote the photocatalytic activity in visible light Theresults indicate the N-TiO
2catalyst prepared with AT ratio
20 and calcinated at 400∘C shows the best photocatalyticability
37 The Formation Mechanism of N-Doped TiO2 For the
pure TiO2 the energy of the visible light is not sufficient
to excite electrons from the valence band (VB) as theintrinsic band gap of pure TiO
2 Based on the results of UV-
vis DRS XRD and XPS the nitrogen atoms were weavedinto the crystal structure of TiO
2with structure as TindashOndash
N N-TiO2was active in the visible light irradiation for
the degradation of ethylene The following explanation forthe photocatalytic activity of N-TiO
2in the visible light
spectra can be consideredThe nitrogen existing at interstitialpositions of TiO
2lattice induces localized occupied states and
forms midband gap leading to the red shift of absorptionedge and photocatalytic activity under visible light irradiation[41] The electron (eminus) can be excited from the N-impuritylevel to the conduction band (CB) The exited electrons aretrapped by O
2adsorbed on the catalyst surface producing
O2
minus∙ superoxide anion radicals After a series of reactions(1)ndash(12) ethylene molecules are finally mineralized into CO
2
DFT calcinations and experimental results indicate that N-doping favored the formation of O vacancy (subband levelO119907) which was below the bottom of the conduction band
[42ndash47] Therefore the electrons (eminus) are excited from theN-impurity level bond to the subband level (O
119907) and then
recombine with the hole (h+) as proved in Figure 9 Theholes and electrons react with OHminus and O
2molecules on the
catalyst surface to form ∙OH radicals and O2
minus∙ superoxideanion radicals respectivelyThe protonation yields theHOO∙radicals which after trapping electrons combine to produceH2O2 The O
2
minus∙ radicals then interact with H2O adsorbed to
produce more ∙OH radicals These ∙OH radicals then reactwith gaseous ethylene and mineralize it
TiO2
h120592997888997888997888997888997888rarr h+ + eminus (1)
SndashH2O + h+ 997888rarr SndashOH∙ +H+ (2)
SndashOHminus + h+ larrrarr SndashOH∙ (3)
S1015840ndashO2+ eminus 997888rarr S1015840ndashO
2
minus∙ (4)
SndashOH + S1015840ndashO2
minus∙997888rarr SndashHO
2
∙+ S1015840ndashOminus∙ (5)
S1015840ndashO2997888rarr 2S1015840ndashO (6)
S1015840ndashO + eminus 997888rarr S1015840ndashOminus∙ (7)
SndashH2O + S1015840ndashOminus∙ 997888rarr SndashOH∙ + SndashOHminus (8)
SndashHO2
∙+ SndashHO
2
∙997888rarr SndashH
2O2+O2
(9)
SndashH2O2997888rarr 2SndashOH∙ (10)
SndashC2H4+ SndashOH∙ larrrarr SndashC
2H4OH (11)
SndashC2H4OH + S1015840ndashO
2997888rarr intermediates 997888rarr CO
2+H2O(12)
4 Conclusions
The observed changes in the UV-vis DRS XRD and XPSspectra are providing consistent structural information forTindashOndashN formation that is the nitrogen can be incorporatedinto the interstitial positions of TiO
2lattice which leads to
the enhanced photocatalytic activity in N-TiO2samples It
is concluded that the photocatalytic oxidation reactivity ofN-TiO
2under visible light illumination is mainly due to the
presence of localized occupied states caused by interstitialnitrogen and the electronhole pairs generated under visiblelight irradiation It has been found that N dopant retardedthe anatase to rutile phase transformation by forming TindashOndashN incorporated into the interstitial position of TiO
2lattice
Moreover the transformation temperatures of anatase-to-rutile progressively slightly increase when N dopant contentis increased The photocatalyst N-TiO
2prepared with AT
ratio 20 and calcinated at 400∘C shows the highest photo-catalytic activity in the oxidation of ethylene This N-TiO
2
provides an effective visible-light-responsive photocatalystfor future industrial applications in pollution control
12 International Journal of Photoenergy
Acknowledgment
This research was financially supported by the NationalScience Council of Taiwan ROC under Grant nos NSC-100-2221-E-005-007 and NSC-100-2120-M-005-002
References
[1] T Horikawa M Katoh and T Tomida ldquoPreparation and char-acterization of nitrogen-doped mesoporous titania with highspecific surface areardquo Microporous and Mesoporous Materialsvol 110 no 2-3 pp 397ndash404 2008
[2] K Yang Y Dai and B Huang ldquoStudy of the nitrogen concen-tration influence onN-dopedTiO
2anatase fromfirst-principles
calculationsrdquo Journal of Physical Chemistry C vol 111 no 32 pp12086ndash12090 2007
[3] K Pomoni A Vomvas and C Trapalis ldquoDark conductivity andtransient photoconductivity of nanocrystalline undoped andN-doped TiO
2sol-gel thin filmsrdquoThin Solid Films vol 516 no 6
pp 1271ndash1278 2008[4] S Sato ldquoPhotocatalytic activity of NO
119909-doped TiO
2in the
visible light regionrdquo Chemical Physics Letters vol 123 no 1-2pp 126ndash128 1986
[5] R Asahi T Morikawa T Ohwaki K Aoki and Y TagaldquoVisible-light photocatalysis in nitrogen-doped titaniumoxidesrdquo Science vol 293 no 5528 pp 269ndash271 2001
[6] J Ananpattarachai P Kajitvichyanukul and S Seraphin ldquoVisi-ble light absorption ability and photocatalytic oxidation activityof various interstitial N-doped TiO
2prepared from different
nitrogen dopantsrdquo Journal of Hazardous Materials vol 168 no1 pp 253ndash261 2009
[7] Y T Lin C HWeng and TW Tzeng ldquoPhotocatalysis and cat-alytic properties of nano-sized N-TiO
2catalyst synthesized by
Sol-gel methodsrdquo Journal of Advanced Oxidation Technologiesvol 13 no 3 pp 297ndash304 2010
[8] B Kosowska S Mozia A W Morawski B Grzmil M Janusand K Kałucki ldquoThe preparation of TiO
2-nitrogen doped by
calcination of TiO2sdot xH2O under ammonia atmosphere for
visible light photocatalysisrdquo Solar Energy Materials and SolarCells vol 88 no 3 pp 269ndash280 2005
[9] F Peng L Cai L Huang H Yu and H Wang ldquoPreparationof nitrogen-doped titanium dioxide with visible-light photocat-alytic activity using a facile hydrothermal methodrdquo Journal ofPhysics and Chemistry of Solids vol 69 no 7 pp 1657ndash16642008
[10] H Yu X Zheng Z Yin F Tag B Fang and K HouldquoPreparation of nitrogen-doped TiO
2nanoparticle catalyst and
its catalytic activity under visible lightrdquo Chinese Journal ofChemical Engineering vol 15 no 6 pp 802ndash807 2007
[11] Z Wang W Cai X Hong X Zhao F Xu and C CaildquoPhotocatalytic degradation of phenol in aqueous nitrogen-doped TiO
2suspensions with various light sourcesrdquo Applied
Catalysis B vol 57 no 3 pp 223ndash231 2005[12] A Trenczek-Zajac K Kowalski K Zakrzewska and M
Radecka ldquoNitrogen-doped titanium dioxidemdashcharacterizationof structural and optical propertiesrdquoMaterials ResearchBulletinvol 44 no 7 pp 1547ndash1552 2009
[13] J S Jang H G Kim S M Ji et al ldquoFormation of crystallineTiO2minus119909
N119909and its photocatalytic activityrdquo Journal of Solid State
Chemistry vol 179 no 4 pp 1067ndash1075 2006[14] H L Qin G B Gu and S Liu ldquoPreparation of nitrogen-doped
titania using sol-gel technique and its photocatalytic activityrdquo
Materials Chemistry and Physics vol 112 no 2 pp 346ndash3522008
[15] J Xu Y Ao D Fu andC Yuan J ldquoLow-temperature preparationof anatase titania-coated magnetiterdquo Journal of Physics andChemistry of Solids vol 69 pp 1980ndash1984 2008
[16] DWuM LongW Cai C Chen and YWu ldquoLow temperaturehydrothermal synthesis of N-doped TiO
2photocatalyst with
high visible-light activityrdquo Journal of Alloys andCompounds vol502 no 2 pp 289ndash294 2010
[17] K M Parida and B Naik ldquoSynthesis of mesoporous TiO2minus119909
N119909
spheres by template free homogeneous co-precipitationmethodand their photo-catalytic activity under visible light illumina-tionrdquo Journal of Colloid and Interface Science vol 333 no 1 pp269ndash276 2009
[18] N R Neti R Misra P K Bera R Dhodapkar S Bakardjievaand Z Bastl ldquoSynthesis of c-doped TiO
2nanoparticles by no-
vel sol-gel polycondensation of resorcinol with formaldehydefor visible-light photocatalysisrdquo Synthesis and Reactivity inInorganic Metal-Organic and Nano-Metal Chemistry vol 40no 5 pp 328ndash332 2010
[19] K Bubacz J Choina D Dolat E Borowiak-Palen D Mos-zynski and A W Morawski ldquoStudies on nitrogen modifiedTiO2photocatalyst prepared in different conditionsrdquoMaterials
Research Bulletin vol 45 no 9 pp 1085ndash1091 2010[20] Z Zhang X Wang J Long Q Gu Z Ding and X Fu
ldquoNitrogen-doped titanium dioxide visible light photocatalystspectroscopic identification of photoactive centersrdquo Journal ofCatalysis vol 276 pp 201ndash214 2010
[21] X Z Bu G K Zhang Y Y Gao and Y Q Yang ldquoPrepara-tion and photocatalytic properties of visible light responsiveN-doped TiO
2rectorite compositesrdquo Microporous and Meso-
porous Materials vol 136 no 1ndash3 pp 132ndash137 2010[22] C Liu X Tang C Mo and Z Qiang ldquoCharacterization and
activity of visible-light-driven TiO2photocatalyst codopedwith
nitrogen and ceriumrdquo Journal of Solid State Chemistry vol 181no 4 pp 913ndash919 2008
[23] R Kun S Tarjan AOszko et al ldquoPreparation and characteriza-tion of mesoporous N-doped and sulfuric acid treated anataseTiO2catalysts and their photocatalytic activity under UV and
Vis illuminationrdquo Journal of Solid State Chemistry vol 182 pp3076ndash3084 2009
[24] Z Pap L Baia K Mogyorosi A Dombi A Oszko and VDanciu ldquoCorrelating the visible light photoactivity of N-dopedTiO2with brookite particle size and bridged-nitro surface
speciesrdquo Catalysis Communications vol 17 pp 1ndash7 2012[25] X Z Bu G K Zhang and CH Zhang ldquoEffect of nitrogen dop-
ing on anatase-rutile phase transformation of TiO2rdquo Applied
Surface Science vol 258 pp 7997ndash8001 2012[26] Y P Peng E Yassitepe Y T Yeh I Ruzybayev S I Shah and C
P Huang ldquoPhotoelectrochemical degradation of azo dye overpulsed laser deposited nitrogen-doped TiO
2thin filmrdquo Applied
Catalysis B vol 125 pp 465ndash472 2012[27] H Jie H B Lee K H Chae et al ldquoNitrogen-doped
TiO2nanopowders prepared by chemical vapor synthesis
band structure and photocatalytic activity under visible lightrdquoResearch on Chemical Intermediates vol 38 no 6 pp 1171ndash11802012
[28] S U M Khan M Al-Shahry and W B Ingler ldquoEfficientphotochemical water splitting by a chemically modified n-TiO2rdquo Science vol 297 no 5590 pp 2243ndash2245 2002
International Journal of Photoenergy 13
[29] X X Wang S Meng X L Zhang H T Wang W Zhong andQ G Du ldquoMulti-type carbon doping of TiO
2photocatalystrdquo
Chemical Physics Letters vol 444 pp 292ndash296 2007[30] N R Khalid E Ahmed Z L Hong Y W Zhang and
M Ahmad ldquoNitrogen doped TiO2nanoparticles decorated
on graphene sheets for photocatalysis applicationsrdquo CurrentApplied Physics vol 12 no 6 pp 1485ndash1492 2012
[31] Q J Xiang J G Yu and M Jaroniec ldquoNitrogen and sulfurco-doped TiO
2nanosheets with exposed 001 facets synthesis
characterization and visible-light photocatalytic activityrdquo Phys-ical Chemistry Chemical Physics vol 13 no 11 pp 4853ndash48612011
[32] J Wang D N Tafen J P Lewis et al ldquoOrigin of photocatalyticactivity of nitrogen-doped TiO
2nanobeltsrdquo Journal of the
American Chemical Society vol 131 pp 12290ndash12297 2009[33] Q Xiang J YuWWang andM Jaroniec ldquoNitrogen self-doped
nanosized TiO2sheets with exposed 001 facets for enhanced
visible-light photocatalytic activityrdquoChemical Communicationsvol 47 no 24 pp 6906ndash6908 2011
[34] Y C Tang X H Huang H Q Yu and L H Tang ldquoNitrogen-doped TiO
2photocatalyst prepared by mechanochemical
method doping mechanisms and visible photoactivity of pol-lutant degradationrdquo International Journal of Photoenergy vol2012 Article ID 960726 10 pages 2012
[35] D E Gu Y Lu B C Yang and Y D Hu ldquoFacile preparationof micro-mesoporous carbon-doped TiO
2photocatalysts with
anatase crystalline walls under template-free conditionrdquo Chem-ical Communications no 21 pp 2453ndash2455 2008
[36] W Ren Z Ai F Jia L Zhang X Fan and Z Zou ldquoLow tem-perature preparation and visible light photocatalytic activity ofmesoporous carbon-doped crystalline TiO
2rdquo Applied Catalysis
B vol 69 no 3-4 pp 138ndash144 2007[37] EM Rockafellow X Fang B G Trewyn K Schmidt-Rohr and
W S Jenks ldquoSolid-state 13C NMR characterization of carbon-modified TiO
2rdquo Chemistry of Materials vol 21 no 7 pp 1187ndash
1197 2009[38] Y Zhang P Xiao X Zhou D Liu B B Garcia and G Cao
ldquoCarbon monoxide annealed TiO2nanotube array electrodes
for efficient biosensor applicationsrdquo Journal of Materials Chem-istry vol 19 no 7 pp 948ndash953 2009
[39] J Yu L Zhang B Cheng andY Su ldquoHydrothermal preparationand photocatalytic activity of hierarchically sponge-like macro-mesoporous Titaniardquo Journal of Physical Chemistry C vol 111no 28 pp 10582ndash10589 2007
[40] J Zhao and X Yang ldquoPhotocatalytic oxidation for indoor airpurification a literature reviewrdquo Building and Environment vol38 no 5 pp 645ndash654 2003
[41] C Di Valentin G Pacchioni and A Selloni ldquoOrigin of thedifferent photoactivity of N-doped anatase and rutile TiO
2rdquo
Physical ReviewB vol 70 no 8 Article ID 085116 4 pages 2004[42] S Livraghi M C Paganini E Giamello A Selloni C
Di Valentin and G Pacchioni ldquoOrigin of photoactivity ofnitrogen-doped titanium dioxide under visible lightrdquo Journal ofthe American Chemical Society vol 128 no 49 pp 15666ndash156712006
[43] X Chen and C Burda ldquoThe electronic origin of the visible-lightabsorption properties of C- N- and S-doped TiO
2nanomateri-
alsrdquo Journal of the American Chemical Society vol 130 no 15pp 5018ndash5019 2008
[44] C Di Valentin G Pacchioni and A Selloni ldquoTheory of carbondoping of titanium dioxiderdquo Chemistry of Materials vol 17 no26 pp 6656ndash6665 2005
[45] HWang and J P Lewis ldquoEffects of dopant states on photoactiv-ity in carbon-dopedTiO
2rdquo Journal of Physics CondensedMatter
vol 17 no 21 pp L209ndashL213 2005[46] H Li D Wang H Fan P Wang T Jiang and T Xie ldquoSynthesis
of highly efficient C-doped TiO2photocatalyst and its photo-
generated charge-transfer propertiesrdquo Journal of Colloid andInterface Science vol 354 no 1 pp 175ndash180 2011
[47] ZWu FDongWZhao and SGuo ldquoVisible light induced elec-tron transfer process over nitrogen doped TiO
2nanocrystals
prepared by oxidation of titaniumnitriderdquo Journal of HazardousMaterials vol 157 no 1 pp 57ndash63 2008
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
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Analytical Methods in Chemistry
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Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Journal of
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Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
4 International Journal of Photoenergy
Table 1 Characteristics for N-TiO2 at various ammoniaTTIP molar ratios under different calcination temperatures
SampleaXRD BET TG-DTA TEM Optical properties
Phase ratio Crystallite size Surface area (m2g) Abrarr Rc Temp (∘C) Size (nm) 1205821198921 1198641198921 1205821198922 1198641198922
Ab Rc Ab (nm) Rc (nm) (nm) (nm) (nm) (nm)A00T4 90 10 32 mdash 93 703 11 plusmn 1 392 316 mdash mdashA05T4 89 11 28 mdash 108 710 12 plusmn 1 392 316 505 246A10T4 90 10 28 mdash 119 720 12 plusmn 1 391 317 506 245A15T4 87 13 29 mdash 119 728 11 plusmn 1 388 320 513 242A20T4 90 10 32 mdash 98 730 12 plusmn 1 390 318 510 243A25T4 90 10 37 mdash 98 728 12 plusmn 1 392 316 515 241A30T4 92 8 37 mdash 86 729 12 plusmn 1 392 316 514 241A00T5 94 6 46 mdash 50 703 13 plusmn 2 402 308 mdash mdashA05T5 89 11 46 98 64 710 13 plusmn 1 404 307 503 247A10T5 90 10 41 87 68 720 15 plusmn 2 400 310 508 244A15T5 91 9 40 mdash 71 728 15 plusmn 2 396 313 517 240A20T5 94 6 45 mdash 62 730 15 plusmn 2 394 315 513 242A25T5 94 6 49 mdash 55 728 17 plusmn 2 397 312 507 245A30T5 94 6 47 mdash 53 729 17 plusmn 2 397 312 510 243A00T6 34 66 106 156 7 703 24 plusmn 2 420 295 mdash mdashA05T6 14 86 86 128 8 710 40 plusmn 3 422 294 mdash mdashA10T6 14 86 81 132 9 720 40 plusmn 4 425 292 mdash mdashA15T6 22 78 79 141 14 728 35 plusmn 3 424 292 mdash mdashA20T6 60 40 85 184 17 730 34 plusmn 3 415 299 mdash mdashA25T6 78 22 90 184 16 728 35 plusmn 4 416 298 mdash mdashA30T6 74 26 97 169 12 729 36 plusmn 4 415 299 mdash mdashA00T7 6 94 131 177 2 703 80 plusmn 5 424 292 mdash mdashA05T7 3 97 95 148 5 710 145 plusmn 10 428 290 mdash mdashA10T7 3 97 102 149 6 720 145 plusmn 10 429 289 mdash mdashA15T7 3 97 92 159 6 728 150 plusmn 11 428 290 mdash mdashA20T7 6 94 103 163 4 730 170 plusmn 13 428 290 mdash mdashA25T7 15 85 108 178 8 728 60 plusmn 6 426 291 mdash mdashA30T7 15 85 117 182 6 729 60 plusmn 6 427 290 mdash mdashA00T8 1 99 mdash 174 3 703 200 plusmn 17 424 292 mdash mdashA05T8 1 99 mdash 161 3 710 190 plusmn 15 428 290 mdash mdashA10T8 1 99 mdash 159 3 720 160 plusmn 13 429 289 mdash mdashA15T8 1 99 mdash 171 3 728 170 plusmn 15 428 290 mdash mdashA20T8 1 99 mdash 164 2 730 160 plusmn 14 428 290 mdash mdashA25T8 3 97 106 184 4 728 200 plusmn 18 427 290 mdash mdashA30T8 3 97 127 179 3 729 170 plusmn 15 429 289 mdash mdashaAXXTY ammoniaTTIP molar ratio = 0XX calcination temperature = Y00∘CbAnatasecRutile
of 400 600 and 700∘C respectively The maximum meansize of anatase and rutile crystallites was observed at 800∘CResults agreed with those reported that the crystalline sizegrows and the content of anatase diminishes as calcinationtemperature increases [8 10ndash13] For the samples prepared at05 AT the anatase peaks appear at temperatures 400 and500∘C Increasing the temperature to 500∘C the intensity ofanatase peak decreases but the rutile peaks appear Whentemperature is increased further to 600∘C rutile becomesa main phase In this case the anatase-to-rutile phasetransformation temperature is between 400 and 500∘C XRD
patterns of samples prepared at 30 AT and annealed at700∘C show both anatase and a rutile phase indicating thatanatase-to-rutile phase transformation is shifted to highertemperature It can be seen that the presence of nitrogencan restrain the formation and growth of TiO
2crystal phase
thereby retarding the anatase-to-rutile phase transformationThis result is further supported by the appearance of rutilein XRD patterns of sample prepared at 05 and 15 GTat 600∘C and disappearance for samples prepared at GTgreater than 20 at 600∘C (data not shown) Comparedwith P25 the peak position of the (101) plane of N-doped
International Journal of Photoenergy 5
A A A
A A
AR
R
RR R R
(101) (110) (004) (204)(200)
(105)(211)
(101)
(111)
(210) (211) (220)
Inte
nsity
(au
)
20 30 40 50 60 70 80
Calcination temperature (∘C)400
500
600
700
800
2120579 (deg)
AT ratio 2
(a)
A A A A A A(101) (004) (204)(200)(105)(211)
Inte
nsity
(au
)
20 30 40 50 60 70 80
0051
15
2253
2120579 (deg)
AT ratio
Calcination temperature 400∘C
P25
(b)
Figure 2 XRD patterns of N-TiO2samples prepared (a) at various calcination temperatures and (b) with various ammoniaTTIP ratios
TiO2shifted slightly to higher 2120579 value and the peak was
broader as NT ratio increases suggesting distortion of thecrystal lattice of TiO
2by the incorporation of nitrogen The
crystalline sizes of samples calcinated at 400∘C and pre-pared at 05 15 20 and 30 AT were 28 29 32 and37 nm respectively The average crystalline size of samplesincreases with increase in AT revealing that nitrogen canenhance the growth of N-TiO
2crystals Results agreed with
those reported that the crystalline size grows as nitrogento Ti proportion increases [14] The results reveal that thephase transformation temperature of anatase to rutile wasprogressively increased when the amount of N dopant wasincreased Clearly calcination temperature andAT ratio playa significant role in the formed crystal structure and particlesize (Figure 3)Higher temperature favors the growth of rutilestructure and produces N-TiO
2nanoparticles with larger
particle size Thus a fine control of calcination temperatureand AT ratio is crucial for obtaining a pure phase of N-TiO
2
Further insights into the effect of calcination and dopingon the morphology and structure of the N-TiO
2samples can
be obtained from HRTEM image (Figure 4) The selectedarea electron diffraction pattern and TEM confirmed itshighly crystalline anatase or rutile structure The observedd-spacing from HRTEM image is 3522 A and is comparableto 352 A previously reported for (101) crystallographic planeof undoped anatase [15ndash18] The HRTEM image showedthe nanocrystallines with primary grain size around 11ndash200 nm From the TEM images the particles in N-TiO
2
samples are monodispersed The crystalline form aggregateswith a mesoporous structure The formation of mesoporousstructure is similar to that reported in the literature [1920] First monodispersed amorphous titanium oxide solparticles are formed by the hydrolysis processes Then themonodispersed sol particles are crystallized and aggregatedunder calcination treatment to form mesoporous crystallineBased on the HRTEM results the calcination temperature
100
80
60
40
20
0400 500 600 700 800Calcination temperature (∘C)
AmmoniaTTIP molar ratio
Ana
tase
()
005115
2253
Figure 3 The anatase content of N-TiO2samples as a function of
the various ammoniaTTIP molar ratios
significantly changes the size of particles (Table 1) The grainsize of crystalline is in consistent with the calculated valueobtained from XRD patterns (Table 1) The grain size ofsamples increases with the calcination temperatureMorpho-logical observation by TEM and XRD calculations revealsthat the large particle size of A20T8 was mainly caused byagglomeration and the growth of crystallite size
33 Surface Area and Pore Size Distribution Typical nitrogenadsorption-desorption isotherms of N-TiO
2photocatalyst
6 International Journal of Photoenergy
400∘C
10nm
(a)
500∘C
10nm
(b)
600∘C
50nm
(c)
700∘C
50nm
(d)
100nm
800∘C
(e) (f)
Figure 4 TEM images of N-TiO2prepared (a)ndash(e) at various calcination temperatures with 20 ammoniaTTIP ratio and (f) the selected
area electron diffraction of A20T4
are shown in Figure 5 The 119878BET of N-TiO2prepared with 20
AT ratio at calcined 400 500 600 700 and 800∘C was 9862 17 4 and 2m2g respectively Obviously the values of119878BET and pore volume of N-TiO
2prepared with the same AT
ratio decreased with increasing calcination temperaturesSuch phenomenon could be attributed to the collapse of themesoporous structure the growth of TiO
2crystallites and
the removal process of nitrogen core by high-temperaturecalcination Consequently N-TiO
2calcined at 800∘C has the
least 119878BET Based on the results obtained the hysteresis loop ofN-TiO
2is significantly shifted in direction of higher relative
pressures as calcination temperature increases indicatingmuch larger mesorpore The average pore size of N-TiO
2
increased with increasing calcination temperature due to theformation of slit-like pores [21]
The N-TiO2samples obtained at various calcination
temperatures gave different nitrogen adsorption isotherms(Figure 5) implying differences in their porous structureThe N-TiO
2samples prepared at low calcination temperature
(ie 400 and 500∘C) exhibited a type IV isotherm and atype H2 hysteresis loop at lower relative pressure regionwhich are typical characteristics of mesoporous structurewith ink bottle pores Note that the adsorption branches ofthese isotherms resembled type II indicating the presence ofsome macropores Otherwise the N-TiO
2samples prepared
at higher calcination temperature (ie 600ndash800∘C) exhibiteda type V isotherm and a type H3 hysteresis loop at higherrelative pressureThe hysteresis loop at lower relative pressureregion (04 lt 119875119875
0lt 08) was attributed to a smaller mes-
opore while that at the higher relative pressure (08 lt1198751198750lt 10) was of larger mesopores Thus samples prepared
at high calcination temperature (gt600∘C) had a wide poresize distribution in the mesopores scale The isotherm of N-TiO2prepared at higher calcination temperature was below
that of lower calcination temperature (Figure 5) indicatinglower surface area and pore volume of the former Furtherobservation from Table 1 indicated that 119878BET for the N-TiO
2
samples at the same AT ratio increased with increasingcalcination temperature (Figure 5(c)) Results reveal thatall N-TiO
2samples calcined at various temperatures show
monomodal pore size distributions and mesopores may beassigned to the pores among interaggregated particles (datanot shown) With calcination temperature increasing thereis a significant tendency of pore size distribution toward tothe bigger pore size The increase of pore size is due to thecorruption of smaller pores during calcination as the smallerpores endured much greater stress than the bigger poresFormation of bigger crystalline aggregation upon increasein temperature could form bigger pores also Consequentlythe pore size increases while the pore volume decreases with
International Journal of Photoenergy 7
200
150
100
50
00 02 04 06 08 1
400500600
700800
IV
IV
V
VV
AmmoniaTTIP ratio 2Calcination temperature (∘C)
Qua
ntity
adso
rbed
(cm
3g
STP
)
Relative pressure (1198751198750)
(a)
0 02 04 06 08 1
005115
2253
IV
250
200
150
100
50
0
H3
Calcination temperature 400∘CAmmoniaTTIP ratio
Qua
ntity
adso
rbed
(cm
3g
STP
)
Relative pressure (1198751198750)
(b)
0
120
100
80
60
40
20
0400 500 600 700 800
Calcination temperature (∘C)
Surfa
ce ar
ea (m
2g
)
05115
2253
AmmoniaTTIP ratio
(c)
Figure 5 Nitrogen adsorption and desorption isotherms of N-TiO2samples (a) calcined at various temperatures (b) prepared with various
ammoniaTTIP molar ratios the surface area as a function of calcination temperature
calcinations temperature increasing Based on the TEM andBET results the mesopores of TiO
2were decreased due
to the heat shrinkage of calcination The results indicatedthat calcination at high temperature and in the presence ofnitrogen atoms will help to improve the thermal stabilityof the photocatalyst While the calcination temperature wasincreased both the specific surface area and the pore vol-ume of N-TiO
2samples decreased This indicated that the
average pore size increased while the pore volume and the
specific surface area decreased with calcination temperatureincreasing
34 Optical Properties The typical UV-vis diffuse reflectancespectra of N-TiO
2are shown in Figures 6(a) and 6(b) It can
be seen that nondoped TiO2(P25) has only one light sharp
edge (120582 = 410 nm) which can be assigned to the band gapof TiO
2 while part of N-TiO
2showed two absorption edges
and a noticeable shift to the visible light region as compared
8 International Journal of Photoenergy
400500600
700800
2
15
1
05
0
Abso
rban
ce (a
u)
Abso
rban
ce (a
u)
200 300 400 500 600 700 800Wavelength (nm)
Wavelength (nm)Calcination temp (∘C)
05
04
03
02
01
0350 400 450 500 550
NTi 2 molar ratiocalcination at different temperatures
AT ratio 2
A20T4A20T5A20T6A20T7A20T8
P25
(a)
2
15
1
05
0
Abso
rban
ce (a
u)
200 300 400 500 600 700 800Wavelength (nm)
Abso
rban
ce (a
u)
Wavelength (nm)
04
04
03
03
02
02
01
01380 400 420 440 460 480 500 520 540
Calcination at 400∘C temperaturedifferent NTi molar ratios
325
215
1050P25
A00T4A05T4A10T4A15T4
A20T4A25T4A30T4
AT ratio
Calcination temperature 400∘C
(b)
Figure 6 The typical UV-vis DR spectra of N-TiO2samples (a) prepared with 20 ammoniaTTIP molar ratio and calcined at various
temperatures (b) prepared with various ammoniaTTIP molar ratios and calcined at 400∘C
to that of the TiO2(ie P25) This phenomenon should be
ascribed to either the nitrogen doping andor sensitizationby a surface-anchored group The calcination temperatureand AT ratio are the crucial factor that can further affectthe absorption as seen in Figure 6 Similar phenomenonhad been reported by previous publications [17 22ndash25] Theabsorption edges of the N-TiO
2samples show continuous
red shift as the calcination temperature changes from 400to 700∘C which can be assigned to the intrinsic band gapabsorption of TiO
2 The shift is too minor to be observed
when the calcination temperature changes from500 to 600∘Cwhich is possibly caused by the synergetic effect of the loss ofthe nitrogen and the increase of the TiO
2crystallinity during
the calcination processThe absorption threshold (120582119892) can be
determined using the onset of the absorption edges by thesection of the fitting lines on the upward and outward sectionof the spectrum (shown in the graph inserted in Figure 6)[23] Table 1 lists the determined 120582
119892(nm) and the derived
band gap energy values The band gap of N-TiO2(119864119892) was
calculated using the 119864119892= 1240120582
119892equation It also can be
seen that N-TiO2samples have two characteristic light
absorption edges One of them corresponds to the band gapof TiO
2(1205821198921= 390sim430 nm) while the other originates from
the N-induced midgap level (1205821198922= 505sim517 nm) The color
of the samples was different with calcination temperatureand AT ratio The color of N-TiO
2samples prepared with
20 AT ratio and calcinated at 400 600 and 700∘C wasvivid yellow yellow and white respectively There is no 120582
1198922
when N-TiO2calcinated above 600∘C It can be ascribed to
the amount of N dopant decreased The color of N-TiO2
prepared with 00 10 20 and 30 AT ratio and calcinatedat 400∘C was white pale yellow yellow and vivid yellow
respectively The phenomenon that the AT ratio increasesthe shifting of the spectra towards visible region was clearlyobserved (Figure 6(a)) The absorption threshold (120582
119892) was
increased with increasing AT ratio It reveals that morenitrogen doping in the matrix of TiO
2structure results in a
shift of absorbance region toward visible light wavelengthThis is possible attribute to the nitrogen incorporated intoTiO2lattice and formation of new electronic state above
valence band caused by nitrogen doping to generate a redshift
35 Analysis of Chemical State The chemical states of dopingimpurity are critical to the optical property band gap andphotocatalytic activity of nitrogen-dopedTiO
2 To investigate
the chemical states of the doping nitrogen XPS spectra wereapplied to examine three regions the Ti 2p core level near460 eV the O 1s core level near 530 eV and the N 1s core levelnear 400 eV Figure 7 shows the experimental observation ofsurface chemical composition and the electronic structuresof N-TiO
2samples using XPS XPS peaks showed that the N-
TiO2contained only Ti O N elements and a small quantity of
carbon The presence of carbon was ascribed to the residualcarbon from the precursor solution and the adventitioushydrocarbon from the XPS instrument itself In Figures 7(a)and 7(b) the binding energy (BE) peaks corresponding toN 1s core levels for N-TiO
2are observed one major peak at
400 eV The N 1s peak at 400 eV is ascribed to the presenceof the oxidized nitrogen species and the nitrogen may beincorporating into the interstitial positions of the TiO
2lattice
and to form a TindashOndashN structure [26 27] No other N 1s peakswere detected in N-TiO
2samples As shown in Figure 7 N 1s
peak at 400 eV slightly decreased with increasing calcination
International Journal of Photoenergy 9
Bind energy (eV)
Inte
nsity
(au
)800
700
600
500
400
Calcination temp (∘C)Ti-O-N
390 395 400 405 410
AT ratio 2
(a)
Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
325
2
15
1
05
0
Ti-O-N
390 395 400 405 410
AT ratio
(b)
Bind energy (eV)
Inte
nsity
(au
) 800
700
600
500
400
Calcination temp (∘C)
Ti-O
524 526 528 530 532 534 536
AT ratio 2
(c)
Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
3
25
2
15
1
05
0
Ti-O
524 526 528 530 532 534 536
AT ratio
(d)
454 456 458 460 462 464 466 468Bind energy (eV)
Inte
nsity
(au
)
4582
4581
4583
458
4583
800
700
600
500
400
Calcination temp (∘C)AT ratio 2Ti4+2p32
Ti4+2p12
(e)
454 456 458 460 462 464 466 468Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
3
25
2
15
1
05
0
Ti4+2p32
Ti4+2p12 AT ratio
(f)
Figure 7 XPS survey and core level spectra of (a)-(b) N 1s (c)-(d) Ti 2p and (e)-(f) O 1s of N-TiO2samples
temperature This is different from the N-TiO2prepared by
flame oxidation in which nitrogen partially substitutes theoxygen sites in the TiO
2[28] The preparation method plays
an important role in determining the nitrogen state in TiO2
band structure [26 29 30]Depending on the nitrogen source
and experimental conditions N species are incorporated intoTiO2in interstitial form or substitutional form [31 32] The
interstitial N-doping is favored when the doping is carriedout under oxygen-rich conditions and the substation-typeN-doping occurs under reducing conditions [31ndash33] Therefore
10 International Journal of Photoenergy
from the atomicN 1sXPS spectra the interstitial sites (400 eV)were observed under air atmosphere
The XPS spectra of Ti 2p regions are shown in Figures7(c) and 7(d) The peaks at around 4585 and 4642 eV forP25 are ascribed to Ti 2p
32and Ti 2p
12of TiO
2(data not
shown)The line separation between Ti 2p12
and Ti 2p32
was57 eV which is consistent with the standard binding energyAccording to Figure 7 all spectra of Ti 2p
12are symmetry
The spectra of Ti 2p12
are consistent of single state and thebanding energy of peaks is 4580ndash4583 eV which shows aredshift of 05 eV compared to the binding energy of Ti4+in P25 This suggests that Ti3+ was present in N-TiO
2and
the distance of peaks between Ti 2p12
and Ti 2p32
is 57ndash59 eV The 396 eV peak is assigned to the atomic b-N stateand generally proves the presence of TiAN bonds formedwhen N atoms replace the oxygen in the TiO
2crystal lattice
[30]The peak characteristic for TindashN (396 eV) is not presentindicating the absence of the TiN phase in the N-TiO
2
samples [34]The results show that the binding energies of Ti2p peaks shift to lower energieswith a negative shift ofsim05 eVfor the N-TiO
2due to the N doping [27] The lower binding
energy than a typical Ti 2p signal of Ti4+ oxidation state sug-gests that titanium cation has a considerable interaction withthe doped nitrogen and thus TiO
2lattice is modified [27
35] Nitrogen doping accompanies the formation of oxygenvacancies andor Ti3+ defects resulting in slight shifts of theTi 2p peak toward the lower binding energy [36ndash38] Hencethe red shifts of the Ti 2p peak in comparison with P25 areused to highlight the successful nitrogen doping into the TiO
2
lattice The XRD results did not indicate the formation ofTiN bondsTherefore results indicate that the titanium atombonds with oxygen but not nitrogen Thus a shift towardlower binding energy of Ti 2p and the binding energy of N1s upon nitrogen addition indicate that the nitrogen can beindeed incorporated into the interstitial positions of TiO
2
lattice and the formation of TindashOndashN bonding by partiallyinterstitial with a carbon atom
The incorporation of nitrogen into the oxide latticeshould influence the BE of O 1s as wellTheXPS spectra of theO 1s core level consists of the one peak (Figures 3(e) and 3(f))at around 5293ndash5295 eV which is ascribed to TindashO bondin the TiO
2lattice [30] The O 1s core level moved toward
lower energy state from 5296 eV in P25 to 5294 eV in N-TiO2prepared with AT ratio 30 and calcined at 400∘C The
peak shifts by sim02 eV which might be related to the creationof oxygen vacancies as a result of the nitrogen doping Theshifting of bind energy in both N 1s and O 1s region indicatesthat nitrogen was incorporated into the lattice The shifts ofTi 2p32
and O 1s peaks are due to the introduction of oxygenvacancies into the TiO
2lattice [32] The presence of nitrogen
dopant facilitates the formation of oxygen vacancies Theaforementioned results clearly indicate that nitrogen dopingis accompanied by oxygen vacancy formation The opticaltransitions between the dopant and dopant-induced level andTi3d orbital explain the observed visible light absorptions ofN-TiO
2nanomaterials The observed two absorbance edge
features in the UV-vis spectra are directly related to the abovemodification of the electronic states from the dopants
50
40
30
20
10
00 05 1 15 2 25 3
AmmoniaTTIP molar ratio
Rem
oval
effici
ency
()
Calcination temp
400∘C
500∘C
800∘C
Figure 8 The removal efficiency of ethylene photooxidation overN-TiO
2as function of the various ammoniaTTIP molar ratios
Experimental conditions [C2H4] = 200 ppmv [H
2O]= 25060 ppmv
[O2] = 21 light intensity = 16mWcm2 temp = 30∘C reaction time
= 3 h
36 Visible Light Photocatalytic Activity To explore the pho-tocatalytic activity of different N-doped TiO
2at different
calcination temperatures and AT ratios the degradationof ethylene under visible light with a cut-off wavelengthof 400 nm was investigated Carbon dioxide started beingformed immediately after the visible light was turned on andethylene was almost totally converted to CO
2in all mea-
surements It is obviously that the N-TiO2shows significant
progress in the photodegradation of ethylene compared toP25 in visible light system P25 has no obvious photocatalyticactivity (less than 1) under visible light irradiation Resultssuggest modification of TiO
2provides visible-light-sensitive
photocatalyst which can be applied to the photooxidationof ethylene gas as the band gap of TiO
2was modified by
nitrogen doping evidenced by XPS and UV-visible DRSresults Figure 8 shows the activity of N-TiO
2catalysts in the
presence of visible light for photodegradation of ethyleneThe reaction rate increases with the increase in the AT ratiofrom 05 to 20 and then decreases in AT ratio from 20to 30 The enhancement of photocatalytic activity can beascribed to an obvious improvement in anatase crystallinityand larger surface area For the sample prepared with ATratio 20 and 30 however the removal efficiency decreasedrapidly which can be due to its less surface area Thephotocatalytic ability of N-TiO
2samples calcinated at 400
500 and 800∘C is also examined It was found that thephotocatalytic activity decreased with increasing calcinationtemperature The enhancement of photocatalytic activitycan be ascribed to an obvious improvement in anatasecrystallinity at 400∘C calcination temperature Good anatasecrystallization is beneficial for reducing the recombinationrate of the photogenerated electrons and holes due to thedecrease in the number of the defects [39] Zhao and Yangshowed that for photocatalytic oxidation application anataseis superior to rutile (a) the conduction band location foranatase is more favorable for driving conjugate reactions
International Journal of Photoenergy 11
32 eVCO2 + H2O
IntermediatesH2O
OH∙ C2H4
eminuseminusTiIII OH
TiIV OH
TiIV OH
O2
∙O2minus
∙HOO H2O2
TiIV OH+∙
CB
VBh+ NS
OV
Figure 9 Schematic diagram for the process in the photooxidation of ethylene and electron transfer process over N-TiO2under visible light
illumination
involving electrons and (b) very stable surface peroxidegroups can be formed at the anatase during photo-oxidationreaction but not on the rutile surface [40] For the samplecalcined at 800∘C the removal efficiency decreased rapidlywhich can be due to its fewer amounts of anatase andsmall 119878BET The result indicates that higher specific surfacearea smaller crystallite size and good anatase crystallizationwill promote the photocatalytic activity in visible light Theresults indicate the N-TiO
2catalyst prepared with AT ratio
20 and calcinated at 400∘C shows the best photocatalyticability
37 The Formation Mechanism of N-Doped TiO2 For the
pure TiO2 the energy of the visible light is not sufficient
to excite electrons from the valence band (VB) as theintrinsic band gap of pure TiO
2 Based on the results of UV-
vis DRS XRD and XPS the nitrogen atoms were weavedinto the crystal structure of TiO
2with structure as TindashOndash
N N-TiO2was active in the visible light irradiation for
the degradation of ethylene The following explanation forthe photocatalytic activity of N-TiO
2in the visible light
spectra can be consideredThe nitrogen existing at interstitialpositions of TiO
2lattice induces localized occupied states and
forms midband gap leading to the red shift of absorptionedge and photocatalytic activity under visible light irradiation[41] The electron (eminus) can be excited from the N-impuritylevel to the conduction band (CB) The exited electrons aretrapped by O
2adsorbed on the catalyst surface producing
O2
minus∙ superoxide anion radicals After a series of reactions(1)ndash(12) ethylene molecules are finally mineralized into CO
2
DFT calcinations and experimental results indicate that N-doping favored the formation of O vacancy (subband levelO119907) which was below the bottom of the conduction band
[42ndash47] Therefore the electrons (eminus) are excited from theN-impurity level bond to the subband level (O
119907) and then
recombine with the hole (h+) as proved in Figure 9 Theholes and electrons react with OHminus and O
2molecules on the
catalyst surface to form ∙OH radicals and O2
minus∙ superoxideanion radicals respectivelyThe protonation yields theHOO∙radicals which after trapping electrons combine to produceH2O2 The O
2
minus∙ radicals then interact with H2O adsorbed to
produce more ∙OH radicals These ∙OH radicals then reactwith gaseous ethylene and mineralize it
TiO2
h120592997888997888997888997888997888rarr h+ + eminus (1)
SndashH2O + h+ 997888rarr SndashOH∙ +H+ (2)
SndashOHminus + h+ larrrarr SndashOH∙ (3)
S1015840ndashO2+ eminus 997888rarr S1015840ndashO
2
minus∙ (4)
SndashOH + S1015840ndashO2
minus∙997888rarr SndashHO
2
∙+ S1015840ndashOminus∙ (5)
S1015840ndashO2997888rarr 2S1015840ndashO (6)
S1015840ndashO + eminus 997888rarr S1015840ndashOminus∙ (7)
SndashH2O + S1015840ndashOminus∙ 997888rarr SndashOH∙ + SndashOHminus (8)
SndashHO2
∙+ SndashHO
2
∙997888rarr SndashH
2O2+O2
(9)
SndashH2O2997888rarr 2SndashOH∙ (10)
SndashC2H4+ SndashOH∙ larrrarr SndashC
2H4OH (11)
SndashC2H4OH + S1015840ndashO
2997888rarr intermediates 997888rarr CO
2+H2O(12)
4 Conclusions
The observed changes in the UV-vis DRS XRD and XPSspectra are providing consistent structural information forTindashOndashN formation that is the nitrogen can be incorporatedinto the interstitial positions of TiO
2lattice which leads to
the enhanced photocatalytic activity in N-TiO2samples It
is concluded that the photocatalytic oxidation reactivity ofN-TiO
2under visible light illumination is mainly due to the
presence of localized occupied states caused by interstitialnitrogen and the electronhole pairs generated under visiblelight irradiation It has been found that N dopant retardedthe anatase to rutile phase transformation by forming TindashOndashN incorporated into the interstitial position of TiO
2lattice
Moreover the transformation temperatures of anatase-to-rutile progressively slightly increase when N dopant contentis increased The photocatalyst N-TiO
2prepared with AT
ratio 20 and calcinated at 400∘C shows the highest photo-catalytic activity in the oxidation of ethylene This N-TiO
2
provides an effective visible-light-responsive photocatalystfor future industrial applications in pollution control
12 International Journal of Photoenergy
Acknowledgment
This research was financially supported by the NationalScience Council of Taiwan ROC under Grant nos NSC-100-2221-E-005-007 and NSC-100-2120-M-005-002
References
[1] T Horikawa M Katoh and T Tomida ldquoPreparation and char-acterization of nitrogen-doped mesoporous titania with highspecific surface areardquo Microporous and Mesoporous Materialsvol 110 no 2-3 pp 397ndash404 2008
[2] K Yang Y Dai and B Huang ldquoStudy of the nitrogen concen-tration influence onN-dopedTiO
2anatase fromfirst-principles
calculationsrdquo Journal of Physical Chemistry C vol 111 no 32 pp12086ndash12090 2007
[3] K Pomoni A Vomvas and C Trapalis ldquoDark conductivity andtransient photoconductivity of nanocrystalline undoped andN-doped TiO
2sol-gel thin filmsrdquoThin Solid Films vol 516 no 6
pp 1271ndash1278 2008[4] S Sato ldquoPhotocatalytic activity of NO
119909-doped TiO
2in the
visible light regionrdquo Chemical Physics Letters vol 123 no 1-2pp 126ndash128 1986
[5] R Asahi T Morikawa T Ohwaki K Aoki and Y TagaldquoVisible-light photocatalysis in nitrogen-doped titaniumoxidesrdquo Science vol 293 no 5528 pp 269ndash271 2001
[6] J Ananpattarachai P Kajitvichyanukul and S Seraphin ldquoVisi-ble light absorption ability and photocatalytic oxidation activityof various interstitial N-doped TiO
2prepared from different
nitrogen dopantsrdquo Journal of Hazardous Materials vol 168 no1 pp 253ndash261 2009
[7] Y T Lin C HWeng and TW Tzeng ldquoPhotocatalysis and cat-alytic properties of nano-sized N-TiO
2catalyst synthesized by
Sol-gel methodsrdquo Journal of Advanced Oxidation Technologiesvol 13 no 3 pp 297ndash304 2010
[8] B Kosowska S Mozia A W Morawski B Grzmil M Janusand K Kałucki ldquoThe preparation of TiO
2-nitrogen doped by
calcination of TiO2sdot xH2O under ammonia atmosphere for
visible light photocatalysisrdquo Solar Energy Materials and SolarCells vol 88 no 3 pp 269ndash280 2005
[9] F Peng L Cai L Huang H Yu and H Wang ldquoPreparationof nitrogen-doped titanium dioxide with visible-light photocat-alytic activity using a facile hydrothermal methodrdquo Journal ofPhysics and Chemistry of Solids vol 69 no 7 pp 1657ndash16642008
[10] H Yu X Zheng Z Yin F Tag B Fang and K HouldquoPreparation of nitrogen-doped TiO
2nanoparticle catalyst and
its catalytic activity under visible lightrdquo Chinese Journal ofChemical Engineering vol 15 no 6 pp 802ndash807 2007
[11] Z Wang W Cai X Hong X Zhao F Xu and C CaildquoPhotocatalytic degradation of phenol in aqueous nitrogen-doped TiO
2suspensions with various light sourcesrdquo Applied
Catalysis B vol 57 no 3 pp 223ndash231 2005[12] A Trenczek-Zajac K Kowalski K Zakrzewska and M
Radecka ldquoNitrogen-doped titanium dioxidemdashcharacterizationof structural and optical propertiesrdquoMaterials ResearchBulletinvol 44 no 7 pp 1547ndash1552 2009
[13] J S Jang H G Kim S M Ji et al ldquoFormation of crystallineTiO2minus119909
N119909and its photocatalytic activityrdquo Journal of Solid State
Chemistry vol 179 no 4 pp 1067ndash1075 2006[14] H L Qin G B Gu and S Liu ldquoPreparation of nitrogen-doped
titania using sol-gel technique and its photocatalytic activityrdquo
Materials Chemistry and Physics vol 112 no 2 pp 346ndash3522008
[15] J Xu Y Ao D Fu andC Yuan J ldquoLow-temperature preparationof anatase titania-coated magnetiterdquo Journal of Physics andChemistry of Solids vol 69 pp 1980ndash1984 2008
[16] DWuM LongW Cai C Chen and YWu ldquoLow temperaturehydrothermal synthesis of N-doped TiO
2photocatalyst with
high visible-light activityrdquo Journal of Alloys andCompounds vol502 no 2 pp 289ndash294 2010
[17] K M Parida and B Naik ldquoSynthesis of mesoporous TiO2minus119909
N119909
spheres by template free homogeneous co-precipitationmethodand their photo-catalytic activity under visible light illumina-tionrdquo Journal of Colloid and Interface Science vol 333 no 1 pp269ndash276 2009
[18] N R Neti R Misra P K Bera R Dhodapkar S Bakardjievaand Z Bastl ldquoSynthesis of c-doped TiO
2nanoparticles by no-
vel sol-gel polycondensation of resorcinol with formaldehydefor visible-light photocatalysisrdquo Synthesis and Reactivity inInorganic Metal-Organic and Nano-Metal Chemistry vol 40no 5 pp 328ndash332 2010
[19] K Bubacz J Choina D Dolat E Borowiak-Palen D Mos-zynski and A W Morawski ldquoStudies on nitrogen modifiedTiO2photocatalyst prepared in different conditionsrdquoMaterials
Research Bulletin vol 45 no 9 pp 1085ndash1091 2010[20] Z Zhang X Wang J Long Q Gu Z Ding and X Fu
ldquoNitrogen-doped titanium dioxide visible light photocatalystspectroscopic identification of photoactive centersrdquo Journal ofCatalysis vol 276 pp 201ndash214 2010
[21] X Z Bu G K Zhang Y Y Gao and Y Q Yang ldquoPrepara-tion and photocatalytic properties of visible light responsiveN-doped TiO
2rectorite compositesrdquo Microporous and Meso-
porous Materials vol 136 no 1ndash3 pp 132ndash137 2010[22] C Liu X Tang C Mo and Z Qiang ldquoCharacterization and
activity of visible-light-driven TiO2photocatalyst codopedwith
nitrogen and ceriumrdquo Journal of Solid State Chemistry vol 181no 4 pp 913ndash919 2008
[23] R Kun S Tarjan AOszko et al ldquoPreparation and characteriza-tion of mesoporous N-doped and sulfuric acid treated anataseTiO2catalysts and their photocatalytic activity under UV and
Vis illuminationrdquo Journal of Solid State Chemistry vol 182 pp3076ndash3084 2009
[24] Z Pap L Baia K Mogyorosi A Dombi A Oszko and VDanciu ldquoCorrelating the visible light photoactivity of N-dopedTiO2with brookite particle size and bridged-nitro surface
speciesrdquo Catalysis Communications vol 17 pp 1ndash7 2012[25] X Z Bu G K Zhang and CH Zhang ldquoEffect of nitrogen dop-
ing on anatase-rutile phase transformation of TiO2rdquo Applied
Surface Science vol 258 pp 7997ndash8001 2012[26] Y P Peng E Yassitepe Y T Yeh I Ruzybayev S I Shah and C
P Huang ldquoPhotoelectrochemical degradation of azo dye overpulsed laser deposited nitrogen-doped TiO
2thin filmrdquo Applied
Catalysis B vol 125 pp 465ndash472 2012[27] H Jie H B Lee K H Chae et al ldquoNitrogen-doped
TiO2nanopowders prepared by chemical vapor synthesis
band structure and photocatalytic activity under visible lightrdquoResearch on Chemical Intermediates vol 38 no 6 pp 1171ndash11802012
[28] S U M Khan M Al-Shahry and W B Ingler ldquoEfficientphotochemical water splitting by a chemically modified n-TiO2rdquo Science vol 297 no 5590 pp 2243ndash2245 2002
International Journal of Photoenergy 13
[29] X X Wang S Meng X L Zhang H T Wang W Zhong andQ G Du ldquoMulti-type carbon doping of TiO
2photocatalystrdquo
Chemical Physics Letters vol 444 pp 292ndash296 2007[30] N R Khalid E Ahmed Z L Hong Y W Zhang and
M Ahmad ldquoNitrogen doped TiO2nanoparticles decorated
on graphene sheets for photocatalysis applicationsrdquo CurrentApplied Physics vol 12 no 6 pp 1485ndash1492 2012
[31] Q J Xiang J G Yu and M Jaroniec ldquoNitrogen and sulfurco-doped TiO
2nanosheets with exposed 001 facets synthesis
characterization and visible-light photocatalytic activityrdquo Phys-ical Chemistry Chemical Physics vol 13 no 11 pp 4853ndash48612011
[32] J Wang D N Tafen J P Lewis et al ldquoOrigin of photocatalyticactivity of nitrogen-doped TiO
2nanobeltsrdquo Journal of the
American Chemical Society vol 131 pp 12290ndash12297 2009[33] Q Xiang J YuWWang andM Jaroniec ldquoNitrogen self-doped
nanosized TiO2sheets with exposed 001 facets for enhanced
visible-light photocatalytic activityrdquoChemical Communicationsvol 47 no 24 pp 6906ndash6908 2011
[34] Y C Tang X H Huang H Q Yu and L H Tang ldquoNitrogen-doped TiO
2photocatalyst prepared by mechanochemical
method doping mechanisms and visible photoactivity of pol-lutant degradationrdquo International Journal of Photoenergy vol2012 Article ID 960726 10 pages 2012
[35] D E Gu Y Lu B C Yang and Y D Hu ldquoFacile preparationof micro-mesoporous carbon-doped TiO
2photocatalysts with
anatase crystalline walls under template-free conditionrdquo Chem-ical Communications no 21 pp 2453ndash2455 2008
[36] W Ren Z Ai F Jia L Zhang X Fan and Z Zou ldquoLow tem-perature preparation and visible light photocatalytic activity ofmesoporous carbon-doped crystalline TiO
2rdquo Applied Catalysis
B vol 69 no 3-4 pp 138ndash144 2007[37] EM Rockafellow X Fang B G Trewyn K Schmidt-Rohr and
W S Jenks ldquoSolid-state 13C NMR characterization of carbon-modified TiO
2rdquo Chemistry of Materials vol 21 no 7 pp 1187ndash
1197 2009[38] Y Zhang P Xiao X Zhou D Liu B B Garcia and G Cao
ldquoCarbon monoxide annealed TiO2nanotube array electrodes
for efficient biosensor applicationsrdquo Journal of Materials Chem-istry vol 19 no 7 pp 948ndash953 2009
[39] J Yu L Zhang B Cheng andY Su ldquoHydrothermal preparationand photocatalytic activity of hierarchically sponge-like macro-mesoporous Titaniardquo Journal of Physical Chemistry C vol 111no 28 pp 10582ndash10589 2007
[40] J Zhao and X Yang ldquoPhotocatalytic oxidation for indoor airpurification a literature reviewrdquo Building and Environment vol38 no 5 pp 645ndash654 2003
[41] C Di Valentin G Pacchioni and A Selloni ldquoOrigin of thedifferent photoactivity of N-doped anatase and rutile TiO
2rdquo
Physical ReviewB vol 70 no 8 Article ID 085116 4 pages 2004[42] S Livraghi M C Paganini E Giamello A Selloni C
Di Valentin and G Pacchioni ldquoOrigin of photoactivity ofnitrogen-doped titanium dioxide under visible lightrdquo Journal ofthe American Chemical Society vol 128 no 49 pp 15666ndash156712006
[43] X Chen and C Burda ldquoThe electronic origin of the visible-lightabsorption properties of C- N- and S-doped TiO
2nanomateri-
alsrdquo Journal of the American Chemical Society vol 130 no 15pp 5018ndash5019 2008
[44] C Di Valentin G Pacchioni and A Selloni ldquoTheory of carbondoping of titanium dioxiderdquo Chemistry of Materials vol 17 no26 pp 6656ndash6665 2005
[45] HWang and J P Lewis ldquoEffects of dopant states on photoactiv-ity in carbon-dopedTiO
2rdquo Journal of Physics CondensedMatter
vol 17 no 21 pp L209ndashL213 2005[46] H Li D Wang H Fan P Wang T Jiang and T Xie ldquoSynthesis
of highly efficient C-doped TiO2photocatalyst and its photo-
generated charge-transfer propertiesrdquo Journal of Colloid andInterface Science vol 354 no 1 pp 175ndash180 2011
[47] ZWu FDongWZhao and SGuo ldquoVisible light induced elec-tron transfer process over nitrogen doped TiO
2nanocrystals
prepared by oxidation of titaniumnitriderdquo Journal of HazardousMaterials vol 157 no 1 pp 57ndash63 2008
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
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Analytical Methods in Chemistry
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Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Journal of
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Analytical ChemistryInternational Journal of
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Quantum Chemistry
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Organic Chemistry International
ElectrochemistryInternational Journal of
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CatalystsJournal of
International Journal of Photoenergy 5
A A A
A A
AR
R
RR R R
(101) (110) (004) (204)(200)
(105)(211)
(101)
(111)
(210) (211) (220)
Inte
nsity
(au
)
20 30 40 50 60 70 80
Calcination temperature (∘C)400
500
600
700
800
2120579 (deg)
AT ratio 2
(a)
A A A A A A(101) (004) (204)(200)(105)(211)
Inte
nsity
(au
)
20 30 40 50 60 70 80
0051
15
2253
2120579 (deg)
AT ratio
Calcination temperature 400∘C
P25
(b)
Figure 2 XRD patterns of N-TiO2samples prepared (a) at various calcination temperatures and (b) with various ammoniaTTIP ratios
TiO2shifted slightly to higher 2120579 value and the peak was
broader as NT ratio increases suggesting distortion of thecrystal lattice of TiO
2by the incorporation of nitrogen The
crystalline sizes of samples calcinated at 400∘C and pre-pared at 05 15 20 and 30 AT were 28 29 32 and37 nm respectively The average crystalline size of samplesincreases with increase in AT revealing that nitrogen canenhance the growth of N-TiO
2crystals Results agreed with
those reported that the crystalline size grows as nitrogento Ti proportion increases [14] The results reveal that thephase transformation temperature of anatase to rutile wasprogressively increased when the amount of N dopant wasincreased Clearly calcination temperature andAT ratio playa significant role in the formed crystal structure and particlesize (Figure 3)Higher temperature favors the growth of rutilestructure and produces N-TiO
2nanoparticles with larger
particle size Thus a fine control of calcination temperatureand AT ratio is crucial for obtaining a pure phase of N-TiO
2
Further insights into the effect of calcination and dopingon the morphology and structure of the N-TiO
2samples can
be obtained from HRTEM image (Figure 4) The selectedarea electron diffraction pattern and TEM confirmed itshighly crystalline anatase or rutile structure The observedd-spacing from HRTEM image is 3522 A and is comparableto 352 A previously reported for (101) crystallographic planeof undoped anatase [15ndash18] The HRTEM image showedthe nanocrystallines with primary grain size around 11ndash200 nm From the TEM images the particles in N-TiO
2
samples are monodispersed The crystalline form aggregateswith a mesoporous structure The formation of mesoporousstructure is similar to that reported in the literature [1920] First monodispersed amorphous titanium oxide solparticles are formed by the hydrolysis processes Then themonodispersed sol particles are crystallized and aggregatedunder calcination treatment to form mesoporous crystallineBased on the HRTEM results the calcination temperature
100
80
60
40
20
0400 500 600 700 800Calcination temperature (∘C)
AmmoniaTTIP molar ratio
Ana
tase
()
005115
2253
Figure 3 The anatase content of N-TiO2samples as a function of
the various ammoniaTTIP molar ratios
significantly changes the size of particles (Table 1) The grainsize of crystalline is in consistent with the calculated valueobtained from XRD patterns (Table 1) The grain size ofsamples increases with the calcination temperatureMorpho-logical observation by TEM and XRD calculations revealsthat the large particle size of A20T8 was mainly caused byagglomeration and the growth of crystallite size
33 Surface Area and Pore Size Distribution Typical nitrogenadsorption-desorption isotherms of N-TiO
2photocatalyst
6 International Journal of Photoenergy
400∘C
10nm
(a)
500∘C
10nm
(b)
600∘C
50nm
(c)
700∘C
50nm
(d)
100nm
800∘C
(e) (f)
Figure 4 TEM images of N-TiO2prepared (a)ndash(e) at various calcination temperatures with 20 ammoniaTTIP ratio and (f) the selected
area electron diffraction of A20T4
are shown in Figure 5 The 119878BET of N-TiO2prepared with 20
AT ratio at calcined 400 500 600 700 and 800∘C was 9862 17 4 and 2m2g respectively Obviously the values of119878BET and pore volume of N-TiO
2prepared with the same AT
ratio decreased with increasing calcination temperaturesSuch phenomenon could be attributed to the collapse of themesoporous structure the growth of TiO
2crystallites and
the removal process of nitrogen core by high-temperaturecalcination Consequently N-TiO
2calcined at 800∘C has the
least 119878BET Based on the results obtained the hysteresis loop ofN-TiO
2is significantly shifted in direction of higher relative
pressures as calcination temperature increases indicatingmuch larger mesorpore The average pore size of N-TiO
2
increased with increasing calcination temperature due to theformation of slit-like pores [21]
The N-TiO2samples obtained at various calcination
temperatures gave different nitrogen adsorption isotherms(Figure 5) implying differences in their porous structureThe N-TiO
2samples prepared at low calcination temperature
(ie 400 and 500∘C) exhibited a type IV isotherm and atype H2 hysteresis loop at lower relative pressure regionwhich are typical characteristics of mesoporous structurewith ink bottle pores Note that the adsorption branches ofthese isotherms resembled type II indicating the presence ofsome macropores Otherwise the N-TiO
2samples prepared
at higher calcination temperature (ie 600ndash800∘C) exhibiteda type V isotherm and a type H3 hysteresis loop at higherrelative pressureThe hysteresis loop at lower relative pressureregion (04 lt 119875119875
0lt 08) was attributed to a smaller mes-
opore while that at the higher relative pressure (08 lt1198751198750lt 10) was of larger mesopores Thus samples prepared
at high calcination temperature (gt600∘C) had a wide poresize distribution in the mesopores scale The isotherm of N-TiO2prepared at higher calcination temperature was below
that of lower calcination temperature (Figure 5) indicatinglower surface area and pore volume of the former Furtherobservation from Table 1 indicated that 119878BET for the N-TiO
2
samples at the same AT ratio increased with increasingcalcination temperature (Figure 5(c)) Results reveal thatall N-TiO
2samples calcined at various temperatures show
monomodal pore size distributions and mesopores may beassigned to the pores among interaggregated particles (datanot shown) With calcination temperature increasing thereis a significant tendency of pore size distribution toward tothe bigger pore size The increase of pore size is due to thecorruption of smaller pores during calcination as the smallerpores endured much greater stress than the bigger poresFormation of bigger crystalline aggregation upon increasein temperature could form bigger pores also Consequentlythe pore size increases while the pore volume decreases with
International Journal of Photoenergy 7
200
150
100
50
00 02 04 06 08 1
400500600
700800
IV
IV
V
VV
AmmoniaTTIP ratio 2Calcination temperature (∘C)
Qua
ntity
adso
rbed
(cm
3g
STP
)
Relative pressure (1198751198750)
(a)
0 02 04 06 08 1
005115
2253
IV
250
200
150
100
50
0
H3
Calcination temperature 400∘CAmmoniaTTIP ratio
Qua
ntity
adso
rbed
(cm
3g
STP
)
Relative pressure (1198751198750)
(b)
0
120
100
80
60
40
20
0400 500 600 700 800
Calcination temperature (∘C)
Surfa
ce ar
ea (m
2g
)
05115
2253
AmmoniaTTIP ratio
(c)
Figure 5 Nitrogen adsorption and desorption isotherms of N-TiO2samples (a) calcined at various temperatures (b) prepared with various
ammoniaTTIP molar ratios the surface area as a function of calcination temperature
calcinations temperature increasing Based on the TEM andBET results the mesopores of TiO
2were decreased due
to the heat shrinkage of calcination The results indicatedthat calcination at high temperature and in the presence ofnitrogen atoms will help to improve the thermal stabilityof the photocatalyst While the calcination temperature wasincreased both the specific surface area and the pore vol-ume of N-TiO
2samples decreased This indicated that the
average pore size increased while the pore volume and the
specific surface area decreased with calcination temperatureincreasing
34 Optical Properties The typical UV-vis diffuse reflectancespectra of N-TiO
2are shown in Figures 6(a) and 6(b) It can
be seen that nondoped TiO2(P25) has only one light sharp
edge (120582 = 410 nm) which can be assigned to the band gapof TiO
2 while part of N-TiO
2showed two absorption edges
and a noticeable shift to the visible light region as compared
8 International Journal of Photoenergy
400500600
700800
2
15
1
05
0
Abso
rban
ce (a
u)
Abso
rban
ce (a
u)
200 300 400 500 600 700 800Wavelength (nm)
Wavelength (nm)Calcination temp (∘C)
05
04
03
02
01
0350 400 450 500 550
NTi 2 molar ratiocalcination at different temperatures
AT ratio 2
A20T4A20T5A20T6A20T7A20T8
P25
(a)
2
15
1
05
0
Abso
rban
ce (a
u)
200 300 400 500 600 700 800Wavelength (nm)
Abso
rban
ce (a
u)
Wavelength (nm)
04
04
03
03
02
02
01
01380 400 420 440 460 480 500 520 540
Calcination at 400∘C temperaturedifferent NTi molar ratios
325
215
1050P25
A00T4A05T4A10T4A15T4
A20T4A25T4A30T4
AT ratio
Calcination temperature 400∘C
(b)
Figure 6 The typical UV-vis DR spectra of N-TiO2samples (a) prepared with 20 ammoniaTTIP molar ratio and calcined at various
temperatures (b) prepared with various ammoniaTTIP molar ratios and calcined at 400∘C
to that of the TiO2(ie P25) This phenomenon should be
ascribed to either the nitrogen doping andor sensitizationby a surface-anchored group The calcination temperatureand AT ratio are the crucial factor that can further affectthe absorption as seen in Figure 6 Similar phenomenonhad been reported by previous publications [17 22ndash25] Theabsorption edges of the N-TiO
2samples show continuous
red shift as the calcination temperature changes from 400to 700∘C which can be assigned to the intrinsic band gapabsorption of TiO
2 The shift is too minor to be observed
when the calcination temperature changes from500 to 600∘Cwhich is possibly caused by the synergetic effect of the loss ofthe nitrogen and the increase of the TiO
2crystallinity during
the calcination processThe absorption threshold (120582119892) can be
determined using the onset of the absorption edges by thesection of the fitting lines on the upward and outward sectionof the spectrum (shown in the graph inserted in Figure 6)[23] Table 1 lists the determined 120582
119892(nm) and the derived
band gap energy values The band gap of N-TiO2(119864119892) was
calculated using the 119864119892= 1240120582
119892equation It also can be
seen that N-TiO2samples have two characteristic light
absorption edges One of them corresponds to the band gapof TiO
2(1205821198921= 390sim430 nm) while the other originates from
the N-induced midgap level (1205821198922= 505sim517 nm) The color
of the samples was different with calcination temperatureand AT ratio The color of N-TiO
2samples prepared with
20 AT ratio and calcinated at 400 600 and 700∘C wasvivid yellow yellow and white respectively There is no 120582
1198922
when N-TiO2calcinated above 600∘C It can be ascribed to
the amount of N dopant decreased The color of N-TiO2
prepared with 00 10 20 and 30 AT ratio and calcinatedat 400∘C was white pale yellow yellow and vivid yellow
respectively The phenomenon that the AT ratio increasesthe shifting of the spectra towards visible region was clearlyobserved (Figure 6(a)) The absorption threshold (120582
119892) was
increased with increasing AT ratio It reveals that morenitrogen doping in the matrix of TiO
2structure results in a
shift of absorbance region toward visible light wavelengthThis is possible attribute to the nitrogen incorporated intoTiO2lattice and formation of new electronic state above
valence band caused by nitrogen doping to generate a redshift
35 Analysis of Chemical State The chemical states of dopingimpurity are critical to the optical property band gap andphotocatalytic activity of nitrogen-dopedTiO
2 To investigate
the chemical states of the doping nitrogen XPS spectra wereapplied to examine three regions the Ti 2p core level near460 eV the O 1s core level near 530 eV and the N 1s core levelnear 400 eV Figure 7 shows the experimental observation ofsurface chemical composition and the electronic structuresof N-TiO
2samples using XPS XPS peaks showed that the N-
TiO2contained only Ti O N elements and a small quantity of
carbon The presence of carbon was ascribed to the residualcarbon from the precursor solution and the adventitioushydrocarbon from the XPS instrument itself In Figures 7(a)and 7(b) the binding energy (BE) peaks corresponding toN 1s core levels for N-TiO
2are observed one major peak at
400 eV The N 1s peak at 400 eV is ascribed to the presenceof the oxidized nitrogen species and the nitrogen may beincorporating into the interstitial positions of the TiO
2lattice
and to form a TindashOndashN structure [26 27] No other N 1s peakswere detected in N-TiO
2samples As shown in Figure 7 N 1s
peak at 400 eV slightly decreased with increasing calcination
International Journal of Photoenergy 9
Bind energy (eV)
Inte
nsity
(au
)800
700
600
500
400
Calcination temp (∘C)Ti-O-N
390 395 400 405 410
AT ratio 2
(a)
Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
325
2
15
1
05
0
Ti-O-N
390 395 400 405 410
AT ratio
(b)
Bind energy (eV)
Inte
nsity
(au
) 800
700
600
500
400
Calcination temp (∘C)
Ti-O
524 526 528 530 532 534 536
AT ratio 2
(c)
Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
3
25
2
15
1
05
0
Ti-O
524 526 528 530 532 534 536
AT ratio
(d)
454 456 458 460 462 464 466 468Bind energy (eV)
Inte
nsity
(au
)
4582
4581
4583
458
4583
800
700
600
500
400
Calcination temp (∘C)AT ratio 2Ti4+2p32
Ti4+2p12
(e)
454 456 458 460 462 464 466 468Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
3
25
2
15
1
05
0
Ti4+2p32
Ti4+2p12 AT ratio
(f)
Figure 7 XPS survey and core level spectra of (a)-(b) N 1s (c)-(d) Ti 2p and (e)-(f) O 1s of N-TiO2samples
temperature This is different from the N-TiO2prepared by
flame oxidation in which nitrogen partially substitutes theoxygen sites in the TiO
2[28] The preparation method plays
an important role in determining the nitrogen state in TiO2
band structure [26 29 30]Depending on the nitrogen source
and experimental conditions N species are incorporated intoTiO2in interstitial form or substitutional form [31 32] The
interstitial N-doping is favored when the doping is carriedout under oxygen-rich conditions and the substation-typeN-doping occurs under reducing conditions [31ndash33] Therefore
10 International Journal of Photoenergy
from the atomicN 1sXPS spectra the interstitial sites (400 eV)were observed under air atmosphere
The XPS spectra of Ti 2p regions are shown in Figures7(c) and 7(d) The peaks at around 4585 and 4642 eV forP25 are ascribed to Ti 2p
32and Ti 2p
12of TiO
2(data not
shown)The line separation between Ti 2p12
and Ti 2p32
was57 eV which is consistent with the standard binding energyAccording to Figure 7 all spectra of Ti 2p
12are symmetry
The spectra of Ti 2p12
are consistent of single state and thebanding energy of peaks is 4580ndash4583 eV which shows aredshift of 05 eV compared to the binding energy of Ti4+in P25 This suggests that Ti3+ was present in N-TiO
2and
the distance of peaks between Ti 2p12
and Ti 2p32
is 57ndash59 eV The 396 eV peak is assigned to the atomic b-N stateand generally proves the presence of TiAN bonds formedwhen N atoms replace the oxygen in the TiO
2crystal lattice
[30]The peak characteristic for TindashN (396 eV) is not presentindicating the absence of the TiN phase in the N-TiO
2
samples [34]The results show that the binding energies of Ti2p peaks shift to lower energieswith a negative shift ofsim05 eVfor the N-TiO
2due to the N doping [27] The lower binding
energy than a typical Ti 2p signal of Ti4+ oxidation state sug-gests that titanium cation has a considerable interaction withthe doped nitrogen and thus TiO
2lattice is modified [27
35] Nitrogen doping accompanies the formation of oxygenvacancies andor Ti3+ defects resulting in slight shifts of theTi 2p peak toward the lower binding energy [36ndash38] Hencethe red shifts of the Ti 2p peak in comparison with P25 areused to highlight the successful nitrogen doping into the TiO
2
lattice The XRD results did not indicate the formation ofTiN bondsTherefore results indicate that the titanium atombonds with oxygen but not nitrogen Thus a shift towardlower binding energy of Ti 2p and the binding energy of N1s upon nitrogen addition indicate that the nitrogen can beindeed incorporated into the interstitial positions of TiO
2
lattice and the formation of TindashOndashN bonding by partiallyinterstitial with a carbon atom
The incorporation of nitrogen into the oxide latticeshould influence the BE of O 1s as wellTheXPS spectra of theO 1s core level consists of the one peak (Figures 3(e) and 3(f))at around 5293ndash5295 eV which is ascribed to TindashO bondin the TiO
2lattice [30] The O 1s core level moved toward
lower energy state from 5296 eV in P25 to 5294 eV in N-TiO2prepared with AT ratio 30 and calcined at 400∘C The
peak shifts by sim02 eV which might be related to the creationof oxygen vacancies as a result of the nitrogen doping Theshifting of bind energy in both N 1s and O 1s region indicatesthat nitrogen was incorporated into the lattice The shifts ofTi 2p32
and O 1s peaks are due to the introduction of oxygenvacancies into the TiO
2lattice [32] The presence of nitrogen
dopant facilitates the formation of oxygen vacancies Theaforementioned results clearly indicate that nitrogen dopingis accompanied by oxygen vacancy formation The opticaltransitions between the dopant and dopant-induced level andTi3d orbital explain the observed visible light absorptions ofN-TiO
2nanomaterials The observed two absorbance edge
features in the UV-vis spectra are directly related to the abovemodification of the electronic states from the dopants
50
40
30
20
10
00 05 1 15 2 25 3
AmmoniaTTIP molar ratio
Rem
oval
effici
ency
()
Calcination temp
400∘C
500∘C
800∘C
Figure 8 The removal efficiency of ethylene photooxidation overN-TiO
2as function of the various ammoniaTTIP molar ratios
Experimental conditions [C2H4] = 200 ppmv [H
2O]= 25060 ppmv
[O2] = 21 light intensity = 16mWcm2 temp = 30∘C reaction time
= 3 h
36 Visible Light Photocatalytic Activity To explore the pho-tocatalytic activity of different N-doped TiO
2at different
calcination temperatures and AT ratios the degradationof ethylene under visible light with a cut-off wavelengthof 400 nm was investigated Carbon dioxide started beingformed immediately after the visible light was turned on andethylene was almost totally converted to CO
2in all mea-
surements It is obviously that the N-TiO2shows significant
progress in the photodegradation of ethylene compared toP25 in visible light system P25 has no obvious photocatalyticactivity (less than 1) under visible light irradiation Resultssuggest modification of TiO
2provides visible-light-sensitive
photocatalyst which can be applied to the photooxidationof ethylene gas as the band gap of TiO
2was modified by
nitrogen doping evidenced by XPS and UV-visible DRSresults Figure 8 shows the activity of N-TiO
2catalysts in the
presence of visible light for photodegradation of ethyleneThe reaction rate increases with the increase in the AT ratiofrom 05 to 20 and then decreases in AT ratio from 20to 30 The enhancement of photocatalytic activity can beascribed to an obvious improvement in anatase crystallinityand larger surface area For the sample prepared with ATratio 20 and 30 however the removal efficiency decreasedrapidly which can be due to its less surface area Thephotocatalytic ability of N-TiO
2samples calcinated at 400
500 and 800∘C is also examined It was found that thephotocatalytic activity decreased with increasing calcinationtemperature The enhancement of photocatalytic activitycan be ascribed to an obvious improvement in anatasecrystallinity at 400∘C calcination temperature Good anatasecrystallization is beneficial for reducing the recombinationrate of the photogenerated electrons and holes due to thedecrease in the number of the defects [39] Zhao and Yangshowed that for photocatalytic oxidation application anataseis superior to rutile (a) the conduction band location foranatase is more favorable for driving conjugate reactions
International Journal of Photoenergy 11
32 eVCO2 + H2O
IntermediatesH2O
OH∙ C2H4
eminuseminusTiIII OH
TiIV OH
TiIV OH
O2
∙O2minus
∙HOO H2O2
TiIV OH+∙
CB
VBh+ NS
OV
Figure 9 Schematic diagram for the process in the photooxidation of ethylene and electron transfer process over N-TiO2under visible light
illumination
involving electrons and (b) very stable surface peroxidegroups can be formed at the anatase during photo-oxidationreaction but not on the rutile surface [40] For the samplecalcined at 800∘C the removal efficiency decreased rapidlywhich can be due to its fewer amounts of anatase andsmall 119878BET The result indicates that higher specific surfacearea smaller crystallite size and good anatase crystallizationwill promote the photocatalytic activity in visible light Theresults indicate the N-TiO
2catalyst prepared with AT ratio
20 and calcinated at 400∘C shows the best photocatalyticability
37 The Formation Mechanism of N-Doped TiO2 For the
pure TiO2 the energy of the visible light is not sufficient
to excite electrons from the valence band (VB) as theintrinsic band gap of pure TiO
2 Based on the results of UV-
vis DRS XRD and XPS the nitrogen atoms were weavedinto the crystal structure of TiO
2with structure as TindashOndash
N N-TiO2was active in the visible light irradiation for
the degradation of ethylene The following explanation forthe photocatalytic activity of N-TiO
2in the visible light
spectra can be consideredThe nitrogen existing at interstitialpositions of TiO
2lattice induces localized occupied states and
forms midband gap leading to the red shift of absorptionedge and photocatalytic activity under visible light irradiation[41] The electron (eminus) can be excited from the N-impuritylevel to the conduction band (CB) The exited electrons aretrapped by O
2adsorbed on the catalyst surface producing
O2
minus∙ superoxide anion radicals After a series of reactions(1)ndash(12) ethylene molecules are finally mineralized into CO
2
DFT calcinations and experimental results indicate that N-doping favored the formation of O vacancy (subband levelO119907) which was below the bottom of the conduction band
[42ndash47] Therefore the electrons (eminus) are excited from theN-impurity level bond to the subband level (O
119907) and then
recombine with the hole (h+) as proved in Figure 9 Theholes and electrons react with OHminus and O
2molecules on the
catalyst surface to form ∙OH radicals and O2
minus∙ superoxideanion radicals respectivelyThe protonation yields theHOO∙radicals which after trapping electrons combine to produceH2O2 The O
2
minus∙ radicals then interact with H2O adsorbed to
produce more ∙OH radicals These ∙OH radicals then reactwith gaseous ethylene and mineralize it
TiO2
h120592997888997888997888997888997888rarr h+ + eminus (1)
SndashH2O + h+ 997888rarr SndashOH∙ +H+ (2)
SndashOHminus + h+ larrrarr SndashOH∙ (3)
S1015840ndashO2+ eminus 997888rarr S1015840ndashO
2
minus∙ (4)
SndashOH + S1015840ndashO2
minus∙997888rarr SndashHO
2
∙+ S1015840ndashOminus∙ (5)
S1015840ndashO2997888rarr 2S1015840ndashO (6)
S1015840ndashO + eminus 997888rarr S1015840ndashOminus∙ (7)
SndashH2O + S1015840ndashOminus∙ 997888rarr SndashOH∙ + SndashOHminus (8)
SndashHO2
∙+ SndashHO
2
∙997888rarr SndashH
2O2+O2
(9)
SndashH2O2997888rarr 2SndashOH∙ (10)
SndashC2H4+ SndashOH∙ larrrarr SndashC
2H4OH (11)
SndashC2H4OH + S1015840ndashO
2997888rarr intermediates 997888rarr CO
2+H2O(12)
4 Conclusions
The observed changes in the UV-vis DRS XRD and XPSspectra are providing consistent structural information forTindashOndashN formation that is the nitrogen can be incorporatedinto the interstitial positions of TiO
2lattice which leads to
the enhanced photocatalytic activity in N-TiO2samples It
is concluded that the photocatalytic oxidation reactivity ofN-TiO
2under visible light illumination is mainly due to the
presence of localized occupied states caused by interstitialnitrogen and the electronhole pairs generated under visiblelight irradiation It has been found that N dopant retardedthe anatase to rutile phase transformation by forming TindashOndashN incorporated into the interstitial position of TiO
2lattice
Moreover the transformation temperatures of anatase-to-rutile progressively slightly increase when N dopant contentis increased The photocatalyst N-TiO
2prepared with AT
ratio 20 and calcinated at 400∘C shows the highest photo-catalytic activity in the oxidation of ethylene This N-TiO
2
provides an effective visible-light-responsive photocatalystfor future industrial applications in pollution control
12 International Journal of Photoenergy
Acknowledgment
This research was financially supported by the NationalScience Council of Taiwan ROC under Grant nos NSC-100-2221-E-005-007 and NSC-100-2120-M-005-002
References
[1] T Horikawa M Katoh and T Tomida ldquoPreparation and char-acterization of nitrogen-doped mesoporous titania with highspecific surface areardquo Microporous and Mesoporous Materialsvol 110 no 2-3 pp 397ndash404 2008
[2] K Yang Y Dai and B Huang ldquoStudy of the nitrogen concen-tration influence onN-dopedTiO
2anatase fromfirst-principles
calculationsrdquo Journal of Physical Chemistry C vol 111 no 32 pp12086ndash12090 2007
[3] K Pomoni A Vomvas and C Trapalis ldquoDark conductivity andtransient photoconductivity of nanocrystalline undoped andN-doped TiO
2sol-gel thin filmsrdquoThin Solid Films vol 516 no 6
pp 1271ndash1278 2008[4] S Sato ldquoPhotocatalytic activity of NO
119909-doped TiO
2in the
visible light regionrdquo Chemical Physics Letters vol 123 no 1-2pp 126ndash128 1986
[5] R Asahi T Morikawa T Ohwaki K Aoki and Y TagaldquoVisible-light photocatalysis in nitrogen-doped titaniumoxidesrdquo Science vol 293 no 5528 pp 269ndash271 2001
[6] J Ananpattarachai P Kajitvichyanukul and S Seraphin ldquoVisi-ble light absorption ability and photocatalytic oxidation activityof various interstitial N-doped TiO
2prepared from different
nitrogen dopantsrdquo Journal of Hazardous Materials vol 168 no1 pp 253ndash261 2009
[7] Y T Lin C HWeng and TW Tzeng ldquoPhotocatalysis and cat-alytic properties of nano-sized N-TiO
2catalyst synthesized by
Sol-gel methodsrdquo Journal of Advanced Oxidation Technologiesvol 13 no 3 pp 297ndash304 2010
[8] B Kosowska S Mozia A W Morawski B Grzmil M Janusand K Kałucki ldquoThe preparation of TiO
2-nitrogen doped by
calcination of TiO2sdot xH2O under ammonia atmosphere for
visible light photocatalysisrdquo Solar Energy Materials and SolarCells vol 88 no 3 pp 269ndash280 2005
[9] F Peng L Cai L Huang H Yu and H Wang ldquoPreparationof nitrogen-doped titanium dioxide with visible-light photocat-alytic activity using a facile hydrothermal methodrdquo Journal ofPhysics and Chemistry of Solids vol 69 no 7 pp 1657ndash16642008
[10] H Yu X Zheng Z Yin F Tag B Fang and K HouldquoPreparation of nitrogen-doped TiO
2nanoparticle catalyst and
its catalytic activity under visible lightrdquo Chinese Journal ofChemical Engineering vol 15 no 6 pp 802ndash807 2007
[11] Z Wang W Cai X Hong X Zhao F Xu and C CaildquoPhotocatalytic degradation of phenol in aqueous nitrogen-doped TiO
2suspensions with various light sourcesrdquo Applied
Catalysis B vol 57 no 3 pp 223ndash231 2005[12] A Trenczek-Zajac K Kowalski K Zakrzewska and M
Radecka ldquoNitrogen-doped titanium dioxidemdashcharacterizationof structural and optical propertiesrdquoMaterials ResearchBulletinvol 44 no 7 pp 1547ndash1552 2009
[13] J S Jang H G Kim S M Ji et al ldquoFormation of crystallineTiO2minus119909
N119909and its photocatalytic activityrdquo Journal of Solid State
Chemistry vol 179 no 4 pp 1067ndash1075 2006[14] H L Qin G B Gu and S Liu ldquoPreparation of nitrogen-doped
titania using sol-gel technique and its photocatalytic activityrdquo
Materials Chemistry and Physics vol 112 no 2 pp 346ndash3522008
[15] J Xu Y Ao D Fu andC Yuan J ldquoLow-temperature preparationof anatase titania-coated magnetiterdquo Journal of Physics andChemistry of Solids vol 69 pp 1980ndash1984 2008
[16] DWuM LongW Cai C Chen and YWu ldquoLow temperaturehydrothermal synthesis of N-doped TiO
2photocatalyst with
high visible-light activityrdquo Journal of Alloys andCompounds vol502 no 2 pp 289ndash294 2010
[17] K M Parida and B Naik ldquoSynthesis of mesoporous TiO2minus119909
N119909
spheres by template free homogeneous co-precipitationmethodand their photo-catalytic activity under visible light illumina-tionrdquo Journal of Colloid and Interface Science vol 333 no 1 pp269ndash276 2009
[18] N R Neti R Misra P K Bera R Dhodapkar S Bakardjievaand Z Bastl ldquoSynthesis of c-doped TiO
2nanoparticles by no-
vel sol-gel polycondensation of resorcinol with formaldehydefor visible-light photocatalysisrdquo Synthesis and Reactivity inInorganic Metal-Organic and Nano-Metal Chemistry vol 40no 5 pp 328ndash332 2010
[19] K Bubacz J Choina D Dolat E Borowiak-Palen D Mos-zynski and A W Morawski ldquoStudies on nitrogen modifiedTiO2photocatalyst prepared in different conditionsrdquoMaterials
Research Bulletin vol 45 no 9 pp 1085ndash1091 2010[20] Z Zhang X Wang J Long Q Gu Z Ding and X Fu
ldquoNitrogen-doped titanium dioxide visible light photocatalystspectroscopic identification of photoactive centersrdquo Journal ofCatalysis vol 276 pp 201ndash214 2010
[21] X Z Bu G K Zhang Y Y Gao and Y Q Yang ldquoPrepara-tion and photocatalytic properties of visible light responsiveN-doped TiO
2rectorite compositesrdquo Microporous and Meso-
porous Materials vol 136 no 1ndash3 pp 132ndash137 2010[22] C Liu X Tang C Mo and Z Qiang ldquoCharacterization and
activity of visible-light-driven TiO2photocatalyst codopedwith
nitrogen and ceriumrdquo Journal of Solid State Chemistry vol 181no 4 pp 913ndash919 2008
[23] R Kun S Tarjan AOszko et al ldquoPreparation and characteriza-tion of mesoporous N-doped and sulfuric acid treated anataseTiO2catalysts and their photocatalytic activity under UV and
Vis illuminationrdquo Journal of Solid State Chemistry vol 182 pp3076ndash3084 2009
[24] Z Pap L Baia K Mogyorosi A Dombi A Oszko and VDanciu ldquoCorrelating the visible light photoactivity of N-dopedTiO2with brookite particle size and bridged-nitro surface
speciesrdquo Catalysis Communications vol 17 pp 1ndash7 2012[25] X Z Bu G K Zhang and CH Zhang ldquoEffect of nitrogen dop-
ing on anatase-rutile phase transformation of TiO2rdquo Applied
Surface Science vol 258 pp 7997ndash8001 2012[26] Y P Peng E Yassitepe Y T Yeh I Ruzybayev S I Shah and C
P Huang ldquoPhotoelectrochemical degradation of azo dye overpulsed laser deposited nitrogen-doped TiO
2thin filmrdquo Applied
Catalysis B vol 125 pp 465ndash472 2012[27] H Jie H B Lee K H Chae et al ldquoNitrogen-doped
TiO2nanopowders prepared by chemical vapor synthesis
band structure and photocatalytic activity under visible lightrdquoResearch on Chemical Intermediates vol 38 no 6 pp 1171ndash11802012
[28] S U M Khan M Al-Shahry and W B Ingler ldquoEfficientphotochemical water splitting by a chemically modified n-TiO2rdquo Science vol 297 no 5590 pp 2243ndash2245 2002
International Journal of Photoenergy 13
[29] X X Wang S Meng X L Zhang H T Wang W Zhong andQ G Du ldquoMulti-type carbon doping of TiO
2photocatalystrdquo
Chemical Physics Letters vol 444 pp 292ndash296 2007[30] N R Khalid E Ahmed Z L Hong Y W Zhang and
M Ahmad ldquoNitrogen doped TiO2nanoparticles decorated
on graphene sheets for photocatalysis applicationsrdquo CurrentApplied Physics vol 12 no 6 pp 1485ndash1492 2012
[31] Q J Xiang J G Yu and M Jaroniec ldquoNitrogen and sulfurco-doped TiO
2nanosheets with exposed 001 facets synthesis
characterization and visible-light photocatalytic activityrdquo Phys-ical Chemistry Chemical Physics vol 13 no 11 pp 4853ndash48612011
[32] J Wang D N Tafen J P Lewis et al ldquoOrigin of photocatalyticactivity of nitrogen-doped TiO
2nanobeltsrdquo Journal of the
American Chemical Society vol 131 pp 12290ndash12297 2009[33] Q Xiang J YuWWang andM Jaroniec ldquoNitrogen self-doped
nanosized TiO2sheets with exposed 001 facets for enhanced
visible-light photocatalytic activityrdquoChemical Communicationsvol 47 no 24 pp 6906ndash6908 2011
[34] Y C Tang X H Huang H Q Yu and L H Tang ldquoNitrogen-doped TiO
2photocatalyst prepared by mechanochemical
method doping mechanisms and visible photoactivity of pol-lutant degradationrdquo International Journal of Photoenergy vol2012 Article ID 960726 10 pages 2012
[35] D E Gu Y Lu B C Yang and Y D Hu ldquoFacile preparationof micro-mesoporous carbon-doped TiO
2photocatalysts with
anatase crystalline walls under template-free conditionrdquo Chem-ical Communications no 21 pp 2453ndash2455 2008
[36] W Ren Z Ai F Jia L Zhang X Fan and Z Zou ldquoLow tem-perature preparation and visible light photocatalytic activity ofmesoporous carbon-doped crystalline TiO
2rdquo Applied Catalysis
B vol 69 no 3-4 pp 138ndash144 2007[37] EM Rockafellow X Fang B G Trewyn K Schmidt-Rohr and
W S Jenks ldquoSolid-state 13C NMR characterization of carbon-modified TiO
2rdquo Chemistry of Materials vol 21 no 7 pp 1187ndash
1197 2009[38] Y Zhang P Xiao X Zhou D Liu B B Garcia and G Cao
ldquoCarbon monoxide annealed TiO2nanotube array electrodes
for efficient biosensor applicationsrdquo Journal of Materials Chem-istry vol 19 no 7 pp 948ndash953 2009
[39] J Yu L Zhang B Cheng andY Su ldquoHydrothermal preparationand photocatalytic activity of hierarchically sponge-like macro-mesoporous Titaniardquo Journal of Physical Chemistry C vol 111no 28 pp 10582ndash10589 2007
[40] J Zhao and X Yang ldquoPhotocatalytic oxidation for indoor airpurification a literature reviewrdquo Building and Environment vol38 no 5 pp 645ndash654 2003
[41] C Di Valentin G Pacchioni and A Selloni ldquoOrigin of thedifferent photoactivity of N-doped anatase and rutile TiO
2rdquo
Physical ReviewB vol 70 no 8 Article ID 085116 4 pages 2004[42] S Livraghi M C Paganini E Giamello A Selloni C
Di Valentin and G Pacchioni ldquoOrigin of photoactivity ofnitrogen-doped titanium dioxide under visible lightrdquo Journal ofthe American Chemical Society vol 128 no 49 pp 15666ndash156712006
[43] X Chen and C Burda ldquoThe electronic origin of the visible-lightabsorption properties of C- N- and S-doped TiO
2nanomateri-
alsrdquo Journal of the American Chemical Society vol 130 no 15pp 5018ndash5019 2008
[44] C Di Valentin G Pacchioni and A Selloni ldquoTheory of carbondoping of titanium dioxiderdquo Chemistry of Materials vol 17 no26 pp 6656ndash6665 2005
[45] HWang and J P Lewis ldquoEffects of dopant states on photoactiv-ity in carbon-dopedTiO
2rdquo Journal of Physics CondensedMatter
vol 17 no 21 pp L209ndashL213 2005[46] H Li D Wang H Fan P Wang T Jiang and T Xie ldquoSynthesis
of highly efficient C-doped TiO2photocatalyst and its photo-
generated charge-transfer propertiesrdquo Journal of Colloid andInterface Science vol 354 no 1 pp 175ndash180 2011
[47] ZWu FDongWZhao and SGuo ldquoVisible light induced elec-tron transfer process over nitrogen doped TiO
2nanocrystals
prepared by oxidation of titaniumnitriderdquo Journal of HazardousMaterials vol 157 no 1 pp 57ndash63 2008
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
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Journal of
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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CatalystsJournal of
6 International Journal of Photoenergy
400∘C
10nm
(a)
500∘C
10nm
(b)
600∘C
50nm
(c)
700∘C
50nm
(d)
100nm
800∘C
(e) (f)
Figure 4 TEM images of N-TiO2prepared (a)ndash(e) at various calcination temperatures with 20 ammoniaTTIP ratio and (f) the selected
area electron diffraction of A20T4
are shown in Figure 5 The 119878BET of N-TiO2prepared with 20
AT ratio at calcined 400 500 600 700 and 800∘C was 9862 17 4 and 2m2g respectively Obviously the values of119878BET and pore volume of N-TiO
2prepared with the same AT
ratio decreased with increasing calcination temperaturesSuch phenomenon could be attributed to the collapse of themesoporous structure the growth of TiO
2crystallites and
the removal process of nitrogen core by high-temperaturecalcination Consequently N-TiO
2calcined at 800∘C has the
least 119878BET Based on the results obtained the hysteresis loop ofN-TiO
2is significantly shifted in direction of higher relative
pressures as calcination temperature increases indicatingmuch larger mesorpore The average pore size of N-TiO
2
increased with increasing calcination temperature due to theformation of slit-like pores [21]
The N-TiO2samples obtained at various calcination
temperatures gave different nitrogen adsorption isotherms(Figure 5) implying differences in their porous structureThe N-TiO
2samples prepared at low calcination temperature
(ie 400 and 500∘C) exhibited a type IV isotherm and atype H2 hysteresis loop at lower relative pressure regionwhich are typical characteristics of mesoporous structurewith ink bottle pores Note that the adsorption branches ofthese isotherms resembled type II indicating the presence ofsome macropores Otherwise the N-TiO
2samples prepared
at higher calcination temperature (ie 600ndash800∘C) exhibiteda type V isotherm and a type H3 hysteresis loop at higherrelative pressureThe hysteresis loop at lower relative pressureregion (04 lt 119875119875
0lt 08) was attributed to a smaller mes-
opore while that at the higher relative pressure (08 lt1198751198750lt 10) was of larger mesopores Thus samples prepared
at high calcination temperature (gt600∘C) had a wide poresize distribution in the mesopores scale The isotherm of N-TiO2prepared at higher calcination temperature was below
that of lower calcination temperature (Figure 5) indicatinglower surface area and pore volume of the former Furtherobservation from Table 1 indicated that 119878BET for the N-TiO
2
samples at the same AT ratio increased with increasingcalcination temperature (Figure 5(c)) Results reveal thatall N-TiO
2samples calcined at various temperatures show
monomodal pore size distributions and mesopores may beassigned to the pores among interaggregated particles (datanot shown) With calcination temperature increasing thereis a significant tendency of pore size distribution toward tothe bigger pore size The increase of pore size is due to thecorruption of smaller pores during calcination as the smallerpores endured much greater stress than the bigger poresFormation of bigger crystalline aggregation upon increasein temperature could form bigger pores also Consequentlythe pore size increases while the pore volume decreases with
International Journal of Photoenergy 7
200
150
100
50
00 02 04 06 08 1
400500600
700800
IV
IV
V
VV
AmmoniaTTIP ratio 2Calcination temperature (∘C)
Qua
ntity
adso
rbed
(cm
3g
STP
)
Relative pressure (1198751198750)
(a)
0 02 04 06 08 1
005115
2253
IV
250
200
150
100
50
0
H3
Calcination temperature 400∘CAmmoniaTTIP ratio
Qua
ntity
adso
rbed
(cm
3g
STP
)
Relative pressure (1198751198750)
(b)
0
120
100
80
60
40
20
0400 500 600 700 800
Calcination temperature (∘C)
Surfa
ce ar
ea (m
2g
)
05115
2253
AmmoniaTTIP ratio
(c)
Figure 5 Nitrogen adsorption and desorption isotherms of N-TiO2samples (a) calcined at various temperatures (b) prepared with various
ammoniaTTIP molar ratios the surface area as a function of calcination temperature
calcinations temperature increasing Based on the TEM andBET results the mesopores of TiO
2were decreased due
to the heat shrinkage of calcination The results indicatedthat calcination at high temperature and in the presence ofnitrogen atoms will help to improve the thermal stabilityof the photocatalyst While the calcination temperature wasincreased both the specific surface area and the pore vol-ume of N-TiO
2samples decreased This indicated that the
average pore size increased while the pore volume and the
specific surface area decreased with calcination temperatureincreasing
34 Optical Properties The typical UV-vis diffuse reflectancespectra of N-TiO
2are shown in Figures 6(a) and 6(b) It can
be seen that nondoped TiO2(P25) has only one light sharp
edge (120582 = 410 nm) which can be assigned to the band gapof TiO
2 while part of N-TiO
2showed two absorption edges
and a noticeable shift to the visible light region as compared
8 International Journal of Photoenergy
400500600
700800
2
15
1
05
0
Abso
rban
ce (a
u)
Abso
rban
ce (a
u)
200 300 400 500 600 700 800Wavelength (nm)
Wavelength (nm)Calcination temp (∘C)
05
04
03
02
01
0350 400 450 500 550
NTi 2 molar ratiocalcination at different temperatures
AT ratio 2
A20T4A20T5A20T6A20T7A20T8
P25
(a)
2
15
1
05
0
Abso
rban
ce (a
u)
200 300 400 500 600 700 800Wavelength (nm)
Abso
rban
ce (a
u)
Wavelength (nm)
04
04
03
03
02
02
01
01380 400 420 440 460 480 500 520 540
Calcination at 400∘C temperaturedifferent NTi molar ratios
325
215
1050P25
A00T4A05T4A10T4A15T4
A20T4A25T4A30T4
AT ratio
Calcination temperature 400∘C
(b)
Figure 6 The typical UV-vis DR spectra of N-TiO2samples (a) prepared with 20 ammoniaTTIP molar ratio and calcined at various
temperatures (b) prepared with various ammoniaTTIP molar ratios and calcined at 400∘C
to that of the TiO2(ie P25) This phenomenon should be
ascribed to either the nitrogen doping andor sensitizationby a surface-anchored group The calcination temperatureand AT ratio are the crucial factor that can further affectthe absorption as seen in Figure 6 Similar phenomenonhad been reported by previous publications [17 22ndash25] Theabsorption edges of the N-TiO
2samples show continuous
red shift as the calcination temperature changes from 400to 700∘C which can be assigned to the intrinsic band gapabsorption of TiO
2 The shift is too minor to be observed
when the calcination temperature changes from500 to 600∘Cwhich is possibly caused by the synergetic effect of the loss ofthe nitrogen and the increase of the TiO
2crystallinity during
the calcination processThe absorption threshold (120582119892) can be
determined using the onset of the absorption edges by thesection of the fitting lines on the upward and outward sectionof the spectrum (shown in the graph inserted in Figure 6)[23] Table 1 lists the determined 120582
119892(nm) and the derived
band gap energy values The band gap of N-TiO2(119864119892) was
calculated using the 119864119892= 1240120582
119892equation It also can be
seen that N-TiO2samples have two characteristic light
absorption edges One of them corresponds to the band gapof TiO
2(1205821198921= 390sim430 nm) while the other originates from
the N-induced midgap level (1205821198922= 505sim517 nm) The color
of the samples was different with calcination temperatureand AT ratio The color of N-TiO
2samples prepared with
20 AT ratio and calcinated at 400 600 and 700∘C wasvivid yellow yellow and white respectively There is no 120582
1198922
when N-TiO2calcinated above 600∘C It can be ascribed to
the amount of N dopant decreased The color of N-TiO2
prepared with 00 10 20 and 30 AT ratio and calcinatedat 400∘C was white pale yellow yellow and vivid yellow
respectively The phenomenon that the AT ratio increasesthe shifting of the spectra towards visible region was clearlyobserved (Figure 6(a)) The absorption threshold (120582
119892) was
increased with increasing AT ratio It reveals that morenitrogen doping in the matrix of TiO
2structure results in a
shift of absorbance region toward visible light wavelengthThis is possible attribute to the nitrogen incorporated intoTiO2lattice and formation of new electronic state above
valence band caused by nitrogen doping to generate a redshift
35 Analysis of Chemical State The chemical states of dopingimpurity are critical to the optical property band gap andphotocatalytic activity of nitrogen-dopedTiO
2 To investigate
the chemical states of the doping nitrogen XPS spectra wereapplied to examine three regions the Ti 2p core level near460 eV the O 1s core level near 530 eV and the N 1s core levelnear 400 eV Figure 7 shows the experimental observation ofsurface chemical composition and the electronic structuresof N-TiO
2samples using XPS XPS peaks showed that the N-
TiO2contained only Ti O N elements and a small quantity of
carbon The presence of carbon was ascribed to the residualcarbon from the precursor solution and the adventitioushydrocarbon from the XPS instrument itself In Figures 7(a)and 7(b) the binding energy (BE) peaks corresponding toN 1s core levels for N-TiO
2are observed one major peak at
400 eV The N 1s peak at 400 eV is ascribed to the presenceof the oxidized nitrogen species and the nitrogen may beincorporating into the interstitial positions of the TiO
2lattice
and to form a TindashOndashN structure [26 27] No other N 1s peakswere detected in N-TiO
2samples As shown in Figure 7 N 1s
peak at 400 eV slightly decreased with increasing calcination
International Journal of Photoenergy 9
Bind energy (eV)
Inte
nsity
(au
)800
700
600
500
400
Calcination temp (∘C)Ti-O-N
390 395 400 405 410
AT ratio 2
(a)
Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
325
2
15
1
05
0
Ti-O-N
390 395 400 405 410
AT ratio
(b)
Bind energy (eV)
Inte
nsity
(au
) 800
700
600
500
400
Calcination temp (∘C)
Ti-O
524 526 528 530 532 534 536
AT ratio 2
(c)
Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
3
25
2
15
1
05
0
Ti-O
524 526 528 530 532 534 536
AT ratio
(d)
454 456 458 460 462 464 466 468Bind energy (eV)
Inte
nsity
(au
)
4582
4581
4583
458
4583
800
700
600
500
400
Calcination temp (∘C)AT ratio 2Ti4+2p32
Ti4+2p12
(e)
454 456 458 460 462 464 466 468Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
3
25
2
15
1
05
0
Ti4+2p32
Ti4+2p12 AT ratio
(f)
Figure 7 XPS survey and core level spectra of (a)-(b) N 1s (c)-(d) Ti 2p and (e)-(f) O 1s of N-TiO2samples
temperature This is different from the N-TiO2prepared by
flame oxidation in which nitrogen partially substitutes theoxygen sites in the TiO
2[28] The preparation method plays
an important role in determining the nitrogen state in TiO2
band structure [26 29 30]Depending on the nitrogen source
and experimental conditions N species are incorporated intoTiO2in interstitial form or substitutional form [31 32] The
interstitial N-doping is favored when the doping is carriedout under oxygen-rich conditions and the substation-typeN-doping occurs under reducing conditions [31ndash33] Therefore
10 International Journal of Photoenergy
from the atomicN 1sXPS spectra the interstitial sites (400 eV)were observed under air atmosphere
The XPS spectra of Ti 2p regions are shown in Figures7(c) and 7(d) The peaks at around 4585 and 4642 eV forP25 are ascribed to Ti 2p
32and Ti 2p
12of TiO
2(data not
shown)The line separation between Ti 2p12
and Ti 2p32
was57 eV which is consistent with the standard binding energyAccording to Figure 7 all spectra of Ti 2p
12are symmetry
The spectra of Ti 2p12
are consistent of single state and thebanding energy of peaks is 4580ndash4583 eV which shows aredshift of 05 eV compared to the binding energy of Ti4+in P25 This suggests that Ti3+ was present in N-TiO
2and
the distance of peaks between Ti 2p12
and Ti 2p32
is 57ndash59 eV The 396 eV peak is assigned to the atomic b-N stateand generally proves the presence of TiAN bonds formedwhen N atoms replace the oxygen in the TiO
2crystal lattice
[30]The peak characteristic for TindashN (396 eV) is not presentindicating the absence of the TiN phase in the N-TiO
2
samples [34]The results show that the binding energies of Ti2p peaks shift to lower energieswith a negative shift ofsim05 eVfor the N-TiO
2due to the N doping [27] The lower binding
energy than a typical Ti 2p signal of Ti4+ oxidation state sug-gests that titanium cation has a considerable interaction withthe doped nitrogen and thus TiO
2lattice is modified [27
35] Nitrogen doping accompanies the formation of oxygenvacancies andor Ti3+ defects resulting in slight shifts of theTi 2p peak toward the lower binding energy [36ndash38] Hencethe red shifts of the Ti 2p peak in comparison with P25 areused to highlight the successful nitrogen doping into the TiO
2
lattice The XRD results did not indicate the formation ofTiN bondsTherefore results indicate that the titanium atombonds with oxygen but not nitrogen Thus a shift towardlower binding energy of Ti 2p and the binding energy of N1s upon nitrogen addition indicate that the nitrogen can beindeed incorporated into the interstitial positions of TiO
2
lattice and the formation of TindashOndashN bonding by partiallyinterstitial with a carbon atom
The incorporation of nitrogen into the oxide latticeshould influence the BE of O 1s as wellTheXPS spectra of theO 1s core level consists of the one peak (Figures 3(e) and 3(f))at around 5293ndash5295 eV which is ascribed to TindashO bondin the TiO
2lattice [30] The O 1s core level moved toward
lower energy state from 5296 eV in P25 to 5294 eV in N-TiO2prepared with AT ratio 30 and calcined at 400∘C The
peak shifts by sim02 eV which might be related to the creationof oxygen vacancies as a result of the nitrogen doping Theshifting of bind energy in both N 1s and O 1s region indicatesthat nitrogen was incorporated into the lattice The shifts ofTi 2p32
and O 1s peaks are due to the introduction of oxygenvacancies into the TiO
2lattice [32] The presence of nitrogen
dopant facilitates the formation of oxygen vacancies Theaforementioned results clearly indicate that nitrogen dopingis accompanied by oxygen vacancy formation The opticaltransitions between the dopant and dopant-induced level andTi3d orbital explain the observed visible light absorptions ofN-TiO
2nanomaterials The observed two absorbance edge
features in the UV-vis spectra are directly related to the abovemodification of the electronic states from the dopants
50
40
30
20
10
00 05 1 15 2 25 3
AmmoniaTTIP molar ratio
Rem
oval
effici
ency
()
Calcination temp
400∘C
500∘C
800∘C
Figure 8 The removal efficiency of ethylene photooxidation overN-TiO
2as function of the various ammoniaTTIP molar ratios
Experimental conditions [C2H4] = 200 ppmv [H
2O]= 25060 ppmv
[O2] = 21 light intensity = 16mWcm2 temp = 30∘C reaction time
= 3 h
36 Visible Light Photocatalytic Activity To explore the pho-tocatalytic activity of different N-doped TiO
2at different
calcination temperatures and AT ratios the degradationof ethylene under visible light with a cut-off wavelengthof 400 nm was investigated Carbon dioxide started beingformed immediately after the visible light was turned on andethylene was almost totally converted to CO
2in all mea-
surements It is obviously that the N-TiO2shows significant
progress in the photodegradation of ethylene compared toP25 in visible light system P25 has no obvious photocatalyticactivity (less than 1) under visible light irradiation Resultssuggest modification of TiO
2provides visible-light-sensitive
photocatalyst which can be applied to the photooxidationof ethylene gas as the band gap of TiO
2was modified by
nitrogen doping evidenced by XPS and UV-visible DRSresults Figure 8 shows the activity of N-TiO
2catalysts in the
presence of visible light for photodegradation of ethyleneThe reaction rate increases with the increase in the AT ratiofrom 05 to 20 and then decreases in AT ratio from 20to 30 The enhancement of photocatalytic activity can beascribed to an obvious improvement in anatase crystallinityand larger surface area For the sample prepared with ATratio 20 and 30 however the removal efficiency decreasedrapidly which can be due to its less surface area Thephotocatalytic ability of N-TiO
2samples calcinated at 400
500 and 800∘C is also examined It was found that thephotocatalytic activity decreased with increasing calcinationtemperature The enhancement of photocatalytic activitycan be ascribed to an obvious improvement in anatasecrystallinity at 400∘C calcination temperature Good anatasecrystallization is beneficial for reducing the recombinationrate of the photogenerated electrons and holes due to thedecrease in the number of the defects [39] Zhao and Yangshowed that for photocatalytic oxidation application anataseis superior to rutile (a) the conduction band location foranatase is more favorable for driving conjugate reactions
International Journal of Photoenergy 11
32 eVCO2 + H2O
IntermediatesH2O
OH∙ C2H4
eminuseminusTiIII OH
TiIV OH
TiIV OH
O2
∙O2minus
∙HOO H2O2
TiIV OH+∙
CB
VBh+ NS
OV
Figure 9 Schematic diagram for the process in the photooxidation of ethylene and electron transfer process over N-TiO2under visible light
illumination
involving electrons and (b) very stable surface peroxidegroups can be formed at the anatase during photo-oxidationreaction but not on the rutile surface [40] For the samplecalcined at 800∘C the removal efficiency decreased rapidlywhich can be due to its fewer amounts of anatase andsmall 119878BET The result indicates that higher specific surfacearea smaller crystallite size and good anatase crystallizationwill promote the photocatalytic activity in visible light Theresults indicate the N-TiO
2catalyst prepared with AT ratio
20 and calcinated at 400∘C shows the best photocatalyticability
37 The Formation Mechanism of N-Doped TiO2 For the
pure TiO2 the energy of the visible light is not sufficient
to excite electrons from the valence band (VB) as theintrinsic band gap of pure TiO
2 Based on the results of UV-
vis DRS XRD and XPS the nitrogen atoms were weavedinto the crystal structure of TiO
2with structure as TindashOndash
N N-TiO2was active in the visible light irradiation for
the degradation of ethylene The following explanation forthe photocatalytic activity of N-TiO
2in the visible light
spectra can be consideredThe nitrogen existing at interstitialpositions of TiO
2lattice induces localized occupied states and
forms midband gap leading to the red shift of absorptionedge and photocatalytic activity under visible light irradiation[41] The electron (eminus) can be excited from the N-impuritylevel to the conduction band (CB) The exited electrons aretrapped by O
2adsorbed on the catalyst surface producing
O2
minus∙ superoxide anion radicals After a series of reactions(1)ndash(12) ethylene molecules are finally mineralized into CO
2
DFT calcinations and experimental results indicate that N-doping favored the formation of O vacancy (subband levelO119907) which was below the bottom of the conduction band
[42ndash47] Therefore the electrons (eminus) are excited from theN-impurity level bond to the subband level (O
119907) and then
recombine with the hole (h+) as proved in Figure 9 Theholes and electrons react with OHminus and O
2molecules on the
catalyst surface to form ∙OH radicals and O2
minus∙ superoxideanion radicals respectivelyThe protonation yields theHOO∙radicals which after trapping electrons combine to produceH2O2 The O
2
minus∙ radicals then interact with H2O adsorbed to
produce more ∙OH radicals These ∙OH radicals then reactwith gaseous ethylene and mineralize it
TiO2
h120592997888997888997888997888997888rarr h+ + eminus (1)
SndashH2O + h+ 997888rarr SndashOH∙ +H+ (2)
SndashOHminus + h+ larrrarr SndashOH∙ (3)
S1015840ndashO2+ eminus 997888rarr S1015840ndashO
2
minus∙ (4)
SndashOH + S1015840ndashO2
minus∙997888rarr SndashHO
2
∙+ S1015840ndashOminus∙ (5)
S1015840ndashO2997888rarr 2S1015840ndashO (6)
S1015840ndashO + eminus 997888rarr S1015840ndashOminus∙ (7)
SndashH2O + S1015840ndashOminus∙ 997888rarr SndashOH∙ + SndashOHminus (8)
SndashHO2
∙+ SndashHO
2
∙997888rarr SndashH
2O2+O2
(9)
SndashH2O2997888rarr 2SndashOH∙ (10)
SndashC2H4+ SndashOH∙ larrrarr SndashC
2H4OH (11)
SndashC2H4OH + S1015840ndashO
2997888rarr intermediates 997888rarr CO
2+H2O(12)
4 Conclusions
The observed changes in the UV-vis DRS XRD and XPSspectra are providing consistent structural information forTindashOndashN formation that is the nitrogen can be incorporatedinto the interstitial positions of TiO
2lattice which leads to
the enhanced photocatalytic activity in N-TiO2samples It
is concluded that the photocatalytic oxidation reactivity ofN-TiO
2under visible light illumination is mainly due to the
presence of localized occupied states caused by interstitialnitrogen and the electronhole pairs generated under visiblelight irradiation It has been found that N dopant retardedthe anatase to rutile phase transformation by forming TindashOndashN incorporated into the interstitial position of TiO
2lattice
Moreover the transformation temperatures of anatase-to-rutile progressively slightly increase when N dopant contentis increased The photocatalyst N-TiO
2prepared with AT
ratio 20 and calcinated at 400∘C shows the highest photo-catalytic activity in the oxidation of ethylene This N-TiO
2
provides an effective visible-light-responsive photocatalystfor future industrial applications in pollution control
12 International Journal of Photoenergy
Acknowledgment
This research was financially supported by the NationalScience Council of Taiwan ROC under Grant nos NSC-100-2221-E-005-007 and NSC-100-2120-M-005-002
References
[1] T Horikawa M Katoh and T Tomida ldquoPreparation and char-acterization of nitrogen-doped mesoporous titania with highspecific surface areardquo Microporous and Mesoporous Materialsvol 110 no 2-3 pp 397ndash404 2008
[2] K Yang Y Dai and B Huang ldquoStudy of the nitrogen concen-tration influence onN-dopedTiO
2anatase fromfirst-principles
calculationsrdquo Journal of Physical Chemistry C vol 111 no 32 pp12086ndash12090 2007
[3] K Pomoni A Vomvas and C Trapalis ldquoDark conductivity andtransient photoconductivity of nanocrystalline undoped andN-doped TiO
2sol-gel thin filmsrdquoThin Solid Films vol 516 no 6
pp 1271ndash1278 2008[4] S Sato ldquoPhotocatalytic activity of NO
119909-doped TiO
2in the
visible light regionrdquo Chemical Physics Letters vol 123 no 1-2pp 126ndash128 1986
[5] R Asahi T Morikawa T Ohwaki K Aoki and Y TagaldquoVisible-light photocatalysis in nitrogen-doped titaniumoxidesrdquo Science vol 293 no 5528 pp 269ndash271 2001
[6] J Ananpattarachai P Kajitvichyanukul and S Seraphin ldquoVisi-ble light absorption ability and photocatalytic oxidation activityof various interstitial N-doped TiO
2prepared from different
nitrogen dopantsrdquo Journal of Hazardous Materials vol 168 no1 pp 253ndash261 2009
[7] Y T Lin C HWeng and TW Tzeng ldquoPhotocatalysis and cat-alytic properties of nano-sized N-TiO
2catalyst synthesized by
Sol-gel methodsrdquo Journal of Advanced Oxidation Technologiesvol 13 no 3 pp 297ndash304 2010
[8] B Kosowska S Mozia A W Morawski B Grzmil M Janusand K Kałucki ldquoThe preparation of TiO
2-nitrogen doped by
calcination of TiO2sdot xH2O under ammonia atmosphere for
visible light photocatalysisrdquo Solar Energy Materials and SolarCells vol 88 no 3 pp 269ndash280 2005
[9] F Peng L Cai L Huang H Yu and H Wang ldquoPreparationof nitrogen-doped titanium dioxide with visible-light photocat-alytic activity using a facile hydrothermal methodrdquo Journal ofPhysics and Chemistry of Solids vol 69 no 7 pp 1657ndash16642008
[10] H Yu X Zheng Z Yin F Tag B Fang and K HouldquoPreparation of nitrogen-doped TiO
2nanoparticle catalyst and
its catalytic activity under visible lightrdquo Chinese Journal ofChemical Engineering vol 15 no 6 pp 802ndash807 2007
[11] Z Wang W Cai X Hong X Zhao F Xu and C CaildquoPhotocatalytic degradation of phenol in aqueous nitrogen-doped TiO
2suspensions with various light sourcesrdquo Applied
Catalysis B vol 57 no 3 pp 223ndash231 2005[12] A Trenczek-Zajac K Kowalski K Zakrzewska and M
Radecka ldquoNitrogen-doped titanium dioxidemdashcharacterizationof structural and optical propertiesrdquoMaterials ResearchBulletinvol 44 no 7 pp 1547ndash1552 2009
[13] J S Jang H G Kim S M Ji et al ldquoFormation of crystallineTiO2minus119909
N119909and its photocatalytic activityrdquo Journal of Solid State
Chemistry vol 179 no 4 pp 1067ndash1075 2006[14] H L Qin G B Gu and S Liu ldquoPreparation of nitrogen-doped
titania using sol-gel technique and its photocatalytic activityrdquo
Materials Chemistry and Physics vol 112 no 2 pp 346ndash3522008
[15] J Xu Y Ao D Fu andC Yuan J ldquoLow-temperature preparationof anatase titania-coated magnetiterdquo Journal of Physics andChemistry of Solids vol 69 pp 1980ndash1984 2008
[16] DWuM LongW Cai C Chen and YWu ldquoLow temperaturehydrothermal synthesis of N-doped TiO
2photocatalyst with
high visible-light activityrdquo Journal of Alloys andCompounds vol502 no 2 pp 289ndash294 2010
[17] K M Parida and B Naik ldquoSynthesis of mesoporous TiO2minus119909
N119909
spheres by template free homogeneous co-precipitationmethodand their photo-catalytic activity under visible light illumina-tionrdquo Journal of Colloid and Interface Science vol 333 no 1 pp269ndash276 2009
[18] N R Neti R Misra P K Bera R Dhodapkar S Bakardjievaand Z Bastl ldquoSynthesis of c-doped TiO
2nanoparticles by no-
vel sol-gel polycondensation of resorcinol with formaldehydefor visible-light photocatalysisrdquo Synthesis and Reactivity inInorganic Metal-Organic and Nano-Metal Chemistry vol 40no 5 pp 328ndash332 2010
[19] K Bubacz J Choina D Dolat E Borowiak-Palen D Mos-zynski and A W Morawski ldquoStudies on nitrogen modifiedTiO2photocatalyst prepared in different conditionsrdquoMaterials
Research Bulletin vol 45 no 9 pp 1085ndash1091 2010[20] Z Zhang X Wang J Long Q Gu Z Ding and X Fu
ldquoNitrogen-doped titanium dioxide visible light photocatalystspectroscopic identification of photoactive centersrdquo Journal ofCatalysis vol 276 pp 201ndash214 2010
[21] X Z Bu G K Zhang Y Y Gao and Y Q Yang ldquoPrepara-tion and photocatalytic properties of visible light responsiveN-doped TiO
2rectorite compositesrdquo Microporous and Meso-
porous Materials vol 136 no 1ndash3 pp 132ndash137 2010[22] C Liu X Tang C Mo and Z Qiang ldquoCharacterization and
activity of visible-light-driven TiO2photocatalyst codopedwith
nitrogen and ceriumrdquo Journal of Solid State Chemistry vol 181no 4 pp 913ndash919 2008
[23] R Kun S Tarjan AOszko et al ldquoPreparation and characteriza-tion of mesoporous N-doped and sulfuric acid treated anataseTiO2catalysts and their photocatalytic activity under UV and
Vis illuminationrdquo Journal of Solid State Chemistry vol 182 pp3076ndash3084 2009
[24] Z Pap L Baia K Mogyorosi A Dombi A Oszko and VDanciu ldquoCorrelating the visible light photoactivity of N-dopedTiO2with brookite particle size and bridged-nitro surface
speciesrdquo Catalysis Communications vol 17 pp 1ndash7 2012[25] X Z Bu G K Zhang and CH Zhang ldquoEffect of nitrogen dop-
ing on anatase-rutile phase transformation of TiO2rdquo Applied
Surface Science vol 258 pp 7997ndash8001 2012[26] Y P Peng E Yassitepe Y T Yeh I Ruzybayev S I Shah and C
P Huang ldquoPhotoelectrochemical degradation of azo dye overpulsed laser deposited nitrogen-doped TiO
2thin filmrdquo Applied
Catalysis B vol 125 pp 465ndash472 2012[27] H Jie H B Lee K H Chae et al ldquoNitrogen-doped
TiO2nanopowders prepared by chemical vapor synthesis
band structure and photocatalytic activity under visible lightrdquoResearch on Chemical Intermediates vol 38 no 6 pp 1171ndash11802012
[28] S U M Khan M Al-Shahry and W B Ingler ldquoEfficientphotochemical water splitting by a chemically modified n-TiO2rdquo Science vol 297 no 5590 pp 2243ndash2245 2002
International Journal of Photoenergy 13
[29] X X Wang S Meng X L Zhang H T Wang W Zhong andQ G Du ldquoMulti-type carbon doping of TiO
2photocatalystrdquo
Chemical Physics Letters vol 444 pp 292ndash296 2007[30] N R Khalid E Ahmed Z L Hong Y W Zhang and
M Ahmad ldquoNitrogen doped TiO2nanoparticles decorated
on graphene sheets for photocatalysis applicationsrdquo CurrentApplied Physics vol 12 no 6 pp 1485ndash1492 2012
[31] Q J Xiang J G Yu and M Jaroniec ldquoNitrogen and sulfurco-doped TiO
2nanosheets with exposed 001 facets synthesis
characterization and visible-light photocatalytic activityrdquo Phys-ical Chemistry Chemical Physics vol 13 no 11 pp 4853ndash48612011
[32] J Wang D N Tafen J P Lewis et al ldquoOrigin of photocatalyticactivity of nitrogen-doped TiO
2nanobeltsrdquo Journal of the
American Chemical Society vol 131 pp 12290ndash12297 2009[33] Q Xiang J YuWWang andM Jaroniec ldquoNitrogen self-doped
nanosized TiO2sheets with exposed 001 facets for enhanced
visible-light photocatalytic activityrdquoChemical Communicationsvol 47 no 24 pp 6906ndash6908 2011
[34] Y C Tang X H Huang H Q Yu and L H Tang ldquoNitrogen-doped TiO
2photocatalyst prepared by mechanochemical
method doping mechanisms and visible photoactivity of pol-lutant degradationrdquo International Journal of Photoenergy vol2012 Article ID 960726 10 pages 2012
[35] D E Gu Y Lu B C Yang and Y D Hu ldquoFacile preparationof micro-mesoporous carbon-doped TiO
2photocatalysts with
anatase crystalline walls under template-free conditionrdquo Chem-ical Communications no 21 pp 2453ndash2455 2008
[36] W Ren Z Ai F Jia L Zhang X Fan and Z Zou ldquoLow tem-perature preparation and visible light photocatalytic activity ofmesoporous carbon-doped crystalline TiO
2rdquo Applied Catalysis
B vol 69 no 3-4 pp 138ndash144 2007[37] EM Rockafellow X Fang B G Trewyn K Schmidt-Rohr and
W S Jenks ldquoSolid-state 13C NMR characterization of carbon-modified TiO
2rdquo Chemistry of Materials vol 21 no 7 pp 1187ndash
1197 2009[38] Y Zhang P Xiao X Zhou D Liu B B Garcia and G Cao
ldquoCarbon monoxide annealed TiO2nanotube array electrodes
for efficient biosensor applicationsrdquo Journal of Materials Chem-istry vol 19 no 7 pp 948ndash953 2009
[39] J Yu L Zhang B Cheng andY Su ldquoHydrothermal preparationand photocatalytic activity of hierarchically sponge-like macro-mesoporous Titaniardquo Journal of Physical Chemistry C vol 111no 28 pp 10582ndash10589 2007
[40] J Zhao and X Yang ldquoPhotocatalytic oxidation for indoor airpurification a literature reviewrdquo Building and Environment vol38 no 5 pp 645ndash654 2003
[41] C Di Valentin G Pacchioni and A Selloni ldquoOrigin of thedifferent photoactivity of N-doped anatase and rutile TiO
2rdquo
Physical ReviewB vol 70 no 8 Article ID 085116 4 pages 2004[42] S Livraghi M C Paganini E Giamello A Selloni C
Di Valentin and G Pacchioni ldquoOrigin of photoactivity ofnitrogen-doped titanium dioxide under visible lightrdquo Journal ofthe American Chemical Society vol 128 no 49 pp 15666ndash156712006
[43] X Chen and C Burda ldquoThe electronic origin of the visible-lightabsorption properties of C- N- and S-doped TiO
2nanomateri-
alsrdquo Journal of the American Chemical Society vol 130 no 15pp 5018ndash5019 2008
[44] C Di Valentin G Pacchioni and A Selloni ldquoTheory of carbondoping of titanium dioxiderdquo Chemistry of Materials vol 17 no26 pp 6656ndash6665 2005
[45] HWang and J P Lewis ldquoEffects of dopant states on photoactiv-ity in carbon-dopedTiO
2rdquo Journal of Physics CondensedMatter
vol 17 no 21 pp L209ndashL213 2005[46] H Li D Wang H Fan P Wang T Jiang and T Xie ldquoSynthesis
of highly efficient C-doped TiO2photocatalyst and its photo-
generated charge-transfer propertiesrdquo Journal of Colloid andInterface Science vol 354 no 1 pp 175ndash180 2011
[47] ZWu FDongWZhao and SGuo ldquoVisible light induced elec-tron transfer process over nitrogen doped TiO
2nanocrystals
prepared by oxidation of titaniumnitriderdquo Journal of HazardousMaterials vol 157 no 1 pp 57ndash63 2008
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
International Journal of Photoenergy 7
200
150
100
50
00 02 04 06 08 1
400500600
700800
IV
IV
V
VV
AmmoniaTTIP ratio 2Calcination temperature (∘C)
Qua
ntity
adso
rbed
(cm
3g
STP
)
Relative pressure (1198751198750)
(a)
0 02 04 06 08 1
005115
2253
IV
250
200
150
100
50
0
H3
Calcination temperature 400∘CAmmoniaTTIP ratio
Qua
ntity
adso
rbed
(cm
3g
STP
)
Relative pressure (1198751198750)
(b)
0
120
100
80
60
40
20
0400 500 600 700 800
Calcination temperature (∘C)
Surfa
ce ar
ea (m
2g
)
05115
2253
AmmoniaTTIP ratio
(c)
Figure 5 Nitrogen adsorption and desorption isotherms of N-TiO2samples (a) calcined at various temperatures (b) prepared with various
ammoniaTTIP molar ratios the surface area as a function of calcination temperature
calcinations temperature increasing Based on the TEM andBET results the mesopores of TiO
2were decreased due
to the heat shrinkage of calcination The results indicatedthat calcination at high temperature and in the presence ofnitrogen atoms will help to improve the thermal stabilityof the photocatalyst While the calcination temperature wasincreased both the specific surface area and the pore vol-ume of N-TiO
2samples decreased This indicated that the
average pore size increased while the pore volume and the
specific surface area decreased with calcination temperatureincreasing
34 Optical Properties The typical UV-vis diffuse reflectancespectra of N-TiO
2are shown in Figures 6(a) and 6(b) It can
be seen that nondoped TiO2(P25) has only one light sharp
edge (120582 = 410 nm) which can be assigned to the band gapof TiO
2 while part of N-TiO
2showed two absorption edges
and a noticeable shift to the visible light region as compared
8 International Journal of Photoenergy
400500600
700800
2
15
1
05
0
Abso
rban
ce (a
u)
Abso
rban
ce (a
u)
200 300 400 500 600 700 800Wavelength (nm)
Wavelength (nm)Calcination temp (∘C)
05
04
03
02
01
0350 400 450 500 550
NTi 2 molar ratiocalcination at different temperatures
AT ratio 2
A20T4A20T5A20T6A20T7A20T8
P25
(a)
2
15
1
05
0
Abso
rban
ce (a
u)
200 300 400 500 600 700 800Wavelength (nm)
Abso
rban
ce (a
u)
Wavelength (nm)
04
04
03
03
02
02
01
01380 400 420 440 460 480 500 520 540
Calcination at 400∘C temperaturedifferent NTi molar ratios
325
215
1050P25
A00T4A05T4A10T4A15T4
A20T4A25T4A30T4
AT ratio
Calcination temperature 400∘C
(b)
Figure 6 The typical UV-vis DR spectra of N-TiO2samples (a) prepared with 20 ammoniaTTIP molar ratio and calcined at various
temperatures (b) prepared with various ammoniaTTIP molar ratios and calcined at 400∘C
to that of the TiO2(ie P25) This phenomenon should be
ascribed to either the nitrogen doping andor sensitizationby a surface-anchored group The calcination temperatureand AT ratio are the crucial factor that can further affectthe absorption as seen in Figure 6 Similar phenomenonhad been reported by previous publications [17 22ndash25] Theabsorption edges of the N-TiO
2samples show continuous
red shift as the calcination temperature changes from 400to 700∘C which can be assigned to the intrinsic band gapabsorption of TiO
2 The shift is too minor to be observed
when the calcination temperature changes from500 to 600∘Cwhich is possibly caused by the synergetic effect of the loss ofthe nitrogen and the increase of the TiO
2crystallinity during
the calcination processThe absorption threshold (120582119892) can be
determined using the onset of the absorption edges by thesection of the fitting lines on the upward and outward sectionof the spectrum (shown in the graph inserted in Figure 6)[23] Table 1 lists the determined 120582
119892(nm) and the derived
band gap energy values The band gap of N-TiO2(119864119892) was
calculated using the 119864119892= 1240120582
119892equation It also can be
seen that N-TiO2samples have two characteristic light
absorption edges One of them corresponds to the band gapof TiO
2(1205821198921= 390sim430 nm) while the other originates from
the N-induced midgap level (1205821198922= 505sim517 nm) The color
of the samples was different with calcination temperatureand AT ratio The color of N-TiO
2samples prepared with
20 AT ratio and calcinated at 400 600 and 700∘C wasvivid yellow yellow and white respectively There is no 120582
1198922
when N-TiO2calcinated above 600∘C It can be ascribed to
the amount of N dopant decreased The color of N-TiO2
prepared with 00 10 20 and 30 AT ratio and calcinatedat 400∘C was white pale yellow yellow and vivid yellow
respectively The phenomenon that the AT ratio increasesthe shifting of the spectra towards visible region was clearlyobserved (Figure 6(a)) The absorption threshold (120582
119892) was
increased with increasing AT ratio It reveals that morenitrogen doping in the matrix of TiO
2structure results in a
shift of absorbance region toward visible light wavelengthThis is possible attribute to the nitrogen incorporated intoTiO2lattice and formation of new electronic state above
valence band caused by nitrogen doping to generate a redshift
35 Analysis of Chemical State The chemical states of dopingimpurity are critical to the optical property band gap andphotocatalytic activity of nitrogen-dopedTiO
2 To investigate
the chemical states of the doping nitrogen XPS spectra wereapplied to examine three regions the Ti 2p core level near460 eV the O 1s core level near 530 eV and the N 1s core levelnear 400 eV Figure 7 shows the experimental observation ofsurface chemical composition and the electronic structuresof N-TiO
2samples using XPS XPS peaks showed that the N-
TiO2contained only Ti O N elements and a small quantity of
carbon The presence of carbon was ascribed to the residualcarbon from the precursor solution and the adventitioushydrocarbon from the XPS instrument itself In Figures 7(a)and 7(b) the binding energy (BE) peaks corresponding toN 1s core levels for N-TiO
2are observed one major peak at
400 eV The N 1s peak at 400 eV is ascribed to the presenceof the oxidized nitrogen species and the nitrogen may beincorporating into the interstitial positions of the TiO
2lattice
and to form a TindashOndashN structure [26 27] No other N 1s peakswere detected in N-TiO
2samples As shown in Figure 7 N 1s
peak at 400 eV slightly decreased with increasing calcination
International Journal of Photoenergy 9
Bind energy (eV)
Inte
nsity
(au
)800
700
600
500
400
Calcination temp (∘C)Ti-O-N
390 395 400 405 410
AT ratio 2
(a)
Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
325
2
15
1
05
0
Ti-O-N
390 395 400 405 410
AT ratio
(b)
Bind energy (eV)
Inte
nsity
(au
) 800
700
600
500
400
Calcination temp (∘C)
Ti-O
524 526 528 530 532 534 536
AT ratio 2
(c)
Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
3
25
2
15
1
05
0
Ti-O
524 526 528 530 532 534 536
AT ratio
(d)
454 456 458 460 462 464 466 468Bind energy (eV)
Inte
nsity
(au
)
4582
4581
4583
458
4583
800
700
600
500
400
Calcination temp (∘C)AT ratio 2Ti4+2p32
Ti4+2p12
(e)
454 456 458 460 462 464 466 468Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
3
25
2
15
1
05
0
Ti4+2p32
Ti4+2p12 AT ratio
(f)
Figure 7 XPS survey and core level spectra of (a)-(b) N 1s (c)-(d) Ti 2p and (e)-(f) O 1s of N-TiO2samples
temperature This is different from the N-TiO2prepared by
flame oxidation in which nitrogen partially substitutes theoxygen sites in the TiO
2[28] The preparation method plays
an important role in determining the nitrogen state in TiO2
band structure [26 29 30]Depending on the nitrogen source
and experimental conditions N species are incorporated intoTiO2in interstitial form or substitutional form [31 32] The
interstitial N-doping is favored when the doping is carriedout under oxygen-rich conditions and the substation-typeN-doping occurs under reducing conditions [31ndash33] Therefore
10 International Journal of Photoenergy
from the atomicN 1sXPS spectra the interstitial sites (400 eV)were observed under air atmosphere
The XPS spectra of Ti 2p regions are shown in Figures7(c) and 7(d) The peaks at around 4585 and 4642 eV forP25 are ascribed to Ti 2p
32and Ti 2p
12of TiO
2(data not
shown)The line separation between Ti 2p12
and Ti 2p32
was57 eV which is consistent with the standard binding energyAccording to Figure 7 all spectra of Ti 2p
12are symmetry
The spectra of Ti 2p12
are consistent of single state and thebanding energy of peaks is 4580ndash4583 eV which shows aredshift of 05 eV compared to the binding energy of Ti4+in P25 This suggests that Ti3+ was present in N-TiO
2and
the distance of peaks between Ti 2p12
and Ti 2p32
is 57ndash59 eV The 396 eV peak is assigned to the atomic b-N stateand generally proves the presence of TiAN bonds formedwhen N atoms replace the oxygen in the TiO
2crystal lattice
[30]The peak characteristic for TindashN (396 eV) is not presentindicating the absence of the TiN phase in the N-TiO
2
samples [34]The results show that the binding energies of Ti2p peaks shift to lower energieswith a negative shift ofsim05 eVfor the N-TiO
2due to the N doping [27] The lower binding
energy than a typical Ti 2p signal of Ti4+ oxidation state sug-gests that titanium cation has a considerable interaction withthe doped nitrogen and thus TiO
2lattice is modified [27
35] Nitrogen doping accompanies the formation of oxygenvacancies andor Ti3+ defects resulting in slight shifts of theTi 2p peak toward the lower binding energy [36ndash38] Hencethe red shifts of the Ti 2p peak in comparison with P25 areused to highlight the successful nitrogen doping into the TiO
2
lattice The XRD results did not indicate the formation ofTiN bondsTherefore results indicate that the titanium atombonds with oxygen but not nitrogen Thus a shift towardlower binding energy of Ti 2p and the binding energy of N1s upon nitrogen addition indicate that the nitrogen can beindeed incorporated into the interstitial positions of TiO
2
lattice and the formation of TindashOndashN bonding by partiallyinterstitial with a carbon atom
The incorporation of nitrogen into the oxide latticeshould influence the BE of O 1s as wellTheXPS spectra of theO 1s core level consists of the one peak (Figures 3(e) and 3(f))at around 5293ndash5295 eV which is ascribed to TindashO bondin the TiO
2lattice [30] The O 1s core level moved toward
lower energy state from 5296 eV in P25 to 5294 eV in N-TiO2prepared with AT ratio 30 and calcined at 400∘C The
peak shifts by sim02 eV which might be related to the creationof oxygen vacancies as a result of the nitrogen doping Theshifting of bind energy in both N 1s and O 1s region indicatesthat nitrogen was incorporated into the lattice The shifts ofTi 2p32
and O 1s peaks are due to the introduction of oxygenvacancies into the TiO
2lattice [32] The presence of nitrogen
dopant facilitates the formation of oxygen vacancies Theaforementioned results clearly indicate that nitrogen dopingis accompanied by oxygen vacancy formation The opticaltransitions between the dopant and dopant-induced level andTi3d orbital explain the observed visible light absorptions ofN-TiO
2nanomaterials The observed two absorbance edge
features in the UV-vis spectra are directly related to the abovemodification of the electronic states from the dopants
50
40
30
20
10
00 05 1 15 2 25 3
AmmoniaTTIP molar ratio
Rem
oval
effici
ency
()
Calcination temp
400∘C
500∘C
800∘C
Figure 8 The removal efficiency of ethylene photooxidation overN-TiO
2as function of the various ammoniaTTIP molar ratios
Experimental conditions [C2H4] = 200 ppmv [H
2O]= 25060 ppmv
[O2] = 21 light intensity = 16mWcm2 temp = 30∘C reaction time
= 3 h
36 Visible Light Photocatalytic Activity To explore the pho-tocatalytic activity of different N-doped TiO
2at different
calcination temperatures and AT ratios the degradationof ethylene under visible light with a cut-off wavelengthof 400 nm was investigated Carbon dioxide started beingformed immediately after the visible light was turned on andethylene was almost totally converted to CO
2in all mea-
surements It is obviously that the N-TiO2shows significant
progress in the photodegradation of ethylene compared toP25 in visible light system P25 has no obvious photocatalyticactivity (less than 1) under visible light irradiation Resultssuggest modification of TiO
2provides visible-light-sensitive
photocatalyst which can be applied to the photooxidationof ethylene gas as the band gap of TiO
2was modified by
nitrogen doping evidenced by XPS and UV-visible DRSresults Figure 8 shows the activity of N-TiO
2catalysts in the
presence of visible light for photodegradation of ethyleneThe reaction rate increases with the increase in the AT ratiofrom 05 to 20 and then decreases in AT ratio from 20to 30 The enhancement of photocatalytic activity can beascribed to an obvious improvement in anatase crystallinityand larger surface area For the sample prepared with ATratio 20 and 30 however the removal efficiency decreasedrapidly which can be due to its less surface area Thephotocatalytic ability of N-TiO
2samples calcinated at 400
500 and 800∘C is also examined It was found that thephotocatalytic activity decreased with increasing calcinationtemperature The enhancement of photocatalytic activitycan be ascribed to an obvious improvement in anatasecrystallinity at 400∘C calcination temperature Good anatasecrystallization is beneficial for reducing the recombinationrate of the photogenerated electrons and holes due to thedecrease in the number of the defects [39] Zhao and Yangshowed that for photocatalytic oxidation application anataseis superior to rutile (a) the conduction band location foranatase is more favorable for driving conjugate reactions
International Journal of Photoenergy 11
32 eVCO2 + H2O
IntermediatesH2O
OH∙ C2H4
eminuseminusTiIII OH
TiIV OH
TiIV OH
O2
∙O2minus
∙HOO H2O2
TiIV OH+∙
CB
VBh+ NS
OV
Figure 9 Schematic diagram for the process in the photooxidation of ethylene and electron transfer process over N-TiO2under visible light
illumination
involving electrons and (b) very stable surface peroxidegroups can be formed at the anatase during photo-oxidationreaction but not on the rutile surface [40] For the samplecalcined at 800∘C the removal efficiency decreased rapidlywhich can be due to its fewer amounts of anatase andsmall 119878BET The result indicates that higher specific surfacearea smaller crystallite size and good anatase crystallizationwill promote the photocatalytic activity in visible light Theresults indicate the N-TiO
2catalyst prepared with AT ratio
20 and calcinated at 400∘C shows the best photocatalyticability
37 The Formation Mechanism of N-Doped TiO2 For the
pure TiO2 the energy of the visible light is not sufficient
to excite electrons from the valence band (VB) as theintrinsic band gap of pure TiO
2 Based on the results of UV-
vis DRS XRD and XPS the nitrogen atoms were weavedinto the crystal structure of TiO
2with structure as TindashOndash
N N-TiO2was active in the visible light irradiation for
the degradation of ethylene The following explanation forthe photocatalytic activity of N-TiO
2in the visible light
spectra can be consideredThe nitrogen existing at interstitialpositions of TiO
2lattice induces localized occupied states and
forms midband gap leading to the red shift of absorptionedge and photocatalytic activity under visible light irradiation[41] The electron (eminus) can be excited from the N-impuritylevel to the conduction band (CB) The exited electrons aretrapped by O
2adsorbed on the catalyst surface producing
O2
minus∙ superoxide anion radicals After a series of reactions(1)ndash(12) ethylene molecules are finally mineralized into CO
2
DFT calcinations and experimental results indicate that N-doping favored the formation of O vacancy (subband levelO119907) which was below the bottom of the conduction band
[42ndash47] Therefore the electrons (eminus) are excited from theN-impurity level bond to the subband level (O
119907) and then
recombine with the hole (h+) as proved in Figure 9 Theholes and electrons react with OHminus and O
2molecules on the
catalyst surface to form ∙OH radicals and O2
minus∙ superoxideanion radicals respectivelyThe protonation yields theHOO∙radicals which after trapping electrons combine to produceH2O2 The O
2
minus∙ radicals then interact with H2O adsorbed to
produce more ∙OH radicals These ∙OH radicals then reactwith gaseous ethylene and mineralize it
TiO2
h120592997888997888997888997888997888rarr h+ + eminus (1)
SndashH2O + h+ 997888rarr SndashOH∙ +H+ (2)
SndashOHminus + h+ larrrarr SndashOH∙ (3)
S1015840ndashO2+ eminus 997888rarr S1015840ndashO
2
minus∙ (4)
SndashOH + S1015840ndashO2
minus∙997888rarr SndashHO
2
∙+ S1015840ndashOminus∙ (5)
S1015840ndashO2997888rarr 2S1015840ndashO (6)
S1015840ndashO + eminus 997888rarr S1015840ndashOminus∙ (7)
SndashH2O + S1015840ndashOminus∙ 997888rarr SndashOH∙ + SndashOHminus (8)
SndashHO2
∙+ SndashHO
2
∙997888rarr SndashH
2O2+O2
(9)
SndashH2O2997888rarr 2SndashOH∙ (10)
SndashC2H4+ SndashOH∙ larrrarr SndashC
2H4OH (11)
SndashC2H4OH + S1015840ndashO
2997888rarr intermediates 997888rarr CO
2+H2O(12)
4 Conclusions
The observed changes in the UV-vis DRS XRD and XPSspectra are providing consistent structural information forTindashOndashN formation that is the nitrogen can be incorporatedinto the interstitial positions of TiO
2lattice which leads to
the enhanced photocatalytic activity in N-TiO2samples It
is concluded that the photocatalytic oxidation reactivity ofN-TiO
2under visible light illumination is mainly due to the
presence of localized occupied states caused by interstitialnitrogen and the electronhole pairs generated under visiblelight irradiation It has been found that N dopant retardedthe anatase to rutile phase transformation by forming TindashOndashN incorporated into the interstitial position of TiO
2lattice
Moreover the transformation temperatures of anatase-to-rutile progressively slightly increase when N dopant contentis increased The photocatalyst N-TiO
2prepared with AT
ratio 20 and calcinated at 400∘C shows the highest photo-catalytic activity in the oxidation of ethylene This N-TiO
2
provides an effective visible-light-responsive photocatalystfor future industrial applications in pollution control
12 International Journal of Photoenergy
Acknowledgment
This research was financially supported by the NationalScience Council of Taiwan ROC under Grant nos NSC-100-2221-E-005-007 and NSC-100-2120-M-005-002
References
[1] T Horikawa M Katoh and T Tomida ldquoPreparation and char-acterization of nitrogen-doped mesoporous titania with highspecific surface areardquo Microporous and Mesoporous Materialsvol 110 no 2-3 pp 397ndash404 2008
[2] K Yang Y Dai and B Huang ldquoStudy of the nitrogen concen-tration influence onN-dopedTiO
2anatase fromfirst-principles
calculationsrdquo Journal of Physical Chemistry C vol 111 no 32 pp12086ndash12090 2007
[3] K Pomoni A Vomvas and C Trapalis ldquoDark conductivity andtransient photoconductivity of nanocrystalline undoped andN-doped TiO
2sol-gel thin filmsrdquoThin Solid Films vol 516 no 6
pp 1271ndash1278 2008[4] S Sato ldquoPhotocatalytic activity of NO
119909-doped TiO
2in the
visible light regionrdquo Chemical Physics Letters vol 123 no 1-2pp 126ndash128 1986
[5] R Asahi T Morikawa T Ohwaki K Aoki and Y TagaldquoVisible-light photocatalysis in nitrogen-doped titaniumoxidesrdquo Science vol 293 no 5528 pp 269ndash271 2001
[6] J Ananpattarachai P Kajitvichyanukul and S Seraphin ldquoVisi-ble light absorption ability and photocatalytic oxidation activityof various interstitial N-doped TiO
2prepared from different
nitrogen dopantsrdquo Journal of Hazardous Materials vol 168 no1 pp 253ndash261 2009
[7] Y T Lin C HWeng and TW Tzeng ldquoPhotocatalysis and cat-alytic properties of nano-sized N-TiO
2catalyst synthesized by
Sol-gel methodsrdquo Journal of Advanced Oxidation Technologiesvol 13 no 3 pp 297ndash304 2010
[8] B Kosowska S Mozia A W Morawski B Grzmil M Janusand K Kałucki ldquoThe preparation of TiO
2-nitrogen doped by
calcination of TiO2sdot xH2O under ammonia atmosphere for
visible light photocatalysisrdquo Solar Energy Materials and SolarCells vol 88 no 3 pp 269ndash280 2005
[9] F Peng L Cai L Huang H Yu and H Wang ldquoPreparationof nitrogen-doped titanium dioxide with visible-light photocat-alytic activity using a facile hydrothermal methodrdquo Journal ofPhysics and Chemistry of Solids vol 69 no 7 pp 1657ndash16642008
[10] H Yu X Zheng Z Yin F Tag B Fang and K HouldquoPreparation of nitrogen-doped TiO
2nanoparticle catalyst and
its catalytic activity under visible lightrdquo Chinese Journal ofChemical Engineering vol 15 no 6 pp 802ndash807 2007
[11] Z Wang W Cai X Hong X Zhao F Xu and C CaildquoPhotocatalytic degradation of phenol in aqueous nitrogen-doped TiO
2suspensions with various light sourcesrdquo Applied
Catalysis B vol 57 no 3 pp 223ndash231 2005[12] A Trenczek-Zajac K Kowalski K Zakrzewska and M
Radecka ldquoNitrogen-doped titanium dioxidemdashcharacterizationof structural and optical propertiesrdquoMaterials ResearchBulletinvol 44 no 7 pp 1547ndash1552 2009
[13] J S Jang H G Kim S M Ji et al ldquoFormation of crystallineTiO2minus119909
N119909and its photocatalytic activityrdquo Journal of Solid State
Chemistry vol 179 no 4 pp 1067ndash1075 2006[14] H L Qin G B Gu and S Liu ldquoPreparation of nitrogen-doped
titania using sol-gel technique and its photocatalytic activityrdquo
Materials Chemistry and Physics vol 112 no 2 pp 346ndash3522008
[15] J Xu Y Ao D Fu andC Yuan J ldquoLow-temperature preparationof anatase titania-coated magnetiterdquo Journal of Physics andChemistry of Solids vol 69 pp 1980ndash1984 2008
[16] DWuM LongW Cai C Chen and YWu ldquoLow temperaturehydrothermal synthesis of N-doped TiO
2photocatalyst with
high visible-light activityrdquo Journal of Alloys andCompounds vol502 no 2 pp 289ndash294 2010
[17] K M Parida and B Naik ldquoSynthesis of mesoporous TiO2minus119909
N119909
spheres by template free homogeneous co-precipitationmethodand their photo-catalytic activity under visible light illumina-tionrdquo Journal of Colloid and Interface Science vol 333 no 1 pp269ndash276 2009
[18] N R Neti R Misra P K Bera R Dhodapkar S Bakardjievaand Z Bastl ldquoSynthesis of c-doped TiO
2nanoparticles by no-
vel sol-gel polycondensation of resorcinol with formaldehydefor visible-light photocatalysisrdquo Synthesis and Reactivity inInorganic Metal-Organic and Nano-Metal Chemistry vol 40no 5 pp 328ndash332 2010
[19] K Bubacz J Choina D Dolat E Borowiak-Palen D Mos-zynski and A W Morawski ldquoStudies on nitrogen modifiedTiO2photocatalyst prepared in different conditionsrdquoMaterials
Research Bulletin vol 45 no 9 pp 1085ndash1091 2010[20] Z Zhang X Wang J Long Q Gu Z Ding and X Fu
ldquoNitrogen-doped titanium dioxide visible light photocatalystspectroscopic identification of photoactive centersrdquo Journal ofCatalysis vol 276 pp 201ndash214 2010
[21] X Z Bu G K Zhang Y Y Gao and Y Q Yang ldquoPrepara-tion and photocatalytic properties of visible light responsiveN-doped TiO
2rectorite compositesrdquo Microporous and Meso-
porous Materials vol 136 no 1ndash3 pp 132ndash137 2010[22] C Liu X Tang C Mo and Z Qiang ldquoCharacterization and
activity of visible-light-driven TiO2photocatalyst codopedwith
nitrogen and ceriumrdquo Journal of Solid State Chemistry vol 181no 4 pp 913ndash919 2008
[23] R Kun S Tarjan AOszko et al ldquoPreparation and characteriza-tion of mesoporous N-doped and sulfuric acid treated anataseTiO2catalysts and their photocatalytic activity under UV and
Vis illuminationrdquo Journal of Solid State Chemistry vol 182 pp3076ndash3084 2009
[24] Z Pap L Baia K Mogyorosi A Dombi A Oszko and VDanciu ldquoCorrelating the visible light photoactivity of N-dopedTiO2with brookite particle size and bridged-nitro surface
speciesrdquo Catalysis Communications vol 17 pp 1ndash7 2012[25] X Z Bu G K Zhang and CH Zhang ldquoEffect of nitrogen dop-
ing on anatase-rutile phase transformation of TiO2rdquo Applied
Surface Science vol 258 pp 7997ndash8001 2012[26] Y P Peng E Yassitepe Y T Yeh I Ruzybayev S I Shah and C
P Huang ldquoPhotoelectrochemical degradation of azo dye overpulsed laser deposited nitrogen-doped TiO
2thin filmrdquo Applied
Catalysis B vol 125 pp 465ndash472 2012[27] H Jie H B Lee K H Chae et al ldquoNitrogen-doped
TiO2nanopowders prepared by chemical vapor synthesis
band structure and photocatalytic activity under visible lightrdquoResearch on Chemical Intermediates vol 38 no 6 pp 1171ndash11802012
[28] S U M Khan M Al-Shahry and W B Ingler ldquoEfficientphotochemical water splitting by a chemically modified n-TiO2rdquo Science vol 297 no 5590 pp 2243ndash2245 2002
International Journal of Photoenergy 13
[29] X X Wang S Meng X L Zhang H T Wang W Zhong andQ G Du ldquoMulti-type carbon doping of TiO
2photocatalystrdquo
Chemical Physics Letters vol 444 pp 292ndash296 2007[30] N R Khalid E Ahmed Z L Hong Y W Zhang and
M Ahmad ldquoNitrogen doped TiO2nanoparticles decorated
on graphene sheets for photocatalysis applicationsrdquo CurrentApplied Physics vol 12 no 6 pp 1485ndash1492 2012
[31] Q J Xiang J G Yu and M Jaroniec ldquoNitrogen and sulfurco-doped TiO
2nanosheets with exposed 001 facets synthesis
characterization and visible-light photocatalytic activityrdquo Phys-ical Chemistry Chemical Physics vol 13 no 11 pp 4853ndash48612011
[32] J Wang D N Tafen J P Lewis et al ldquoOrigin of photocatalyticactivity of nitrogen-doped TiO
2nanobeltsrdquo Journal of the
American Chemical Society vol 131 pp 12290ndash12297 2009[33] Q Xiang J YuWWang andM Jaroniec ldquoNitrogen self-doped
nanosized TiO2sheets with exposed 001 facets for enhanced
visible-light photocatalytic activityrdquoChemical Communicationsvol 47 no 24 pp 6906ndash6908 2011
[34] Y C Tang X H Huang H Q Yu and L H Tang ldquoNitrogen-doped TiO
2photocatalyst prepared by mechanochemical
method doping mechanisms and visible photoactivity of pol-lutant degradationrdquo International Journal of Photoenergy vol2012 Article ID 960726 10 pages 2012
[35] D E Gu Y Lu B C Yang and Y D Hu ldquoFacile preparationof micro-mesoporous carbon-doped TiO
2photocatalysts with
anatase crystalline walls under template-free conditionrdquo Chem-ical Communications no 21 pp 2453ndash2455 2008
[36] W Ren Z Ai F Jia L Zhang X Fan and Z Zou ldquoLow tem-perature preparation and visible light photocatalytic activity ofmesoporous carbon-doped crystalline TiO
2rdquo Applied Catalysis
B vol 69 no 3-4 pp 138ndash144 2007[37] EM Rockafellow X Fang B G Trewyn K Schmidt-Rohr and
W S Jenks ldquoSolid-state 13C NMR characterization of carbon-modified TiO
2rdquo Chemistry of Materials vol 21 no 7 pp 1187ndash
1197 2009[38] Y Zhang P Xiao X Zhou D Liu B B Garcia and G Cao
ldquoCarbon monoxide annealed TiO2nanotube array electrodes
for efficient biosensor applicationsrdquo Journal of Materials Chem-istry vol 19 no 7 pp 948ndash953 2009
[39] J Yu L Zhang B Cheng andY Su ldquoHydrothermal preparationand photocatalytic activity of hierarchically sponge-like macro-mesoporous Titaniardquo Journal of Physical Chemistry C vol 111no 28 pp 10582ndash10589 2007
[40] J Zhao and X Yang ldquoPhotocatalytic oxidation for indoor airpurification a literature reviewrdquo Building and Environment vol38 no 5 pp 645ndash654 2003
[41] C Di Valentin G Pacchioni and A Selloni ldquoOrigin of thedifferent photoactivity of N-doped anatase and rutile TiO
2rdquo
Physical ReviewB vol 70 no 8 Article ID 085116 4 pages 2004[42] S Livraghi M C Paganini E Giamello A Selloni C
Di Valentin and G Pacchioni ldquoOrigin of photoactivity ofnitrogen-doped titanium dioxide under visible lightrdquo Journal ofthe American Chemical Society vol 128 no 49 pp 15666ndash156712006
[43] X Chen and C Burda ldquoThe electronic origin of the visible-lightabsorption properties of C- N- and S-doped TiO
2nanomateri-
alsrdquo Journal of the American Chemical Society vol 130 no 15pp 5018ndash5019 2008
[44] C Di Valentin G Pacchioni and A Selloni ldquoTheory of carbondoping of titanium dioxiderdquo Chemistry of Materials vol 17 no26 pp 6656ndash6665 2005
[45] HWang and J P Lewis ldquoEffects of dopant states on photoactiv-ity in carbon-dopedTiO
2rdquo Journal of Physics CondensedMatter
vol 17 no 21 pp L209ndashL213 2005[46] H Li D Wang H Fan P Wang T Jiang and T Xie ldquoSynthesis
of highly efficient C-doped TiO2photocatalyst and its photo-
generated charge-transfer propertiesrdquo Journal of Colloid andInterface Science vol 354 no 1 pp 175ndash180 2011
[47] ZWu FDongWZhao and SGuo ldquoVisible light induced elec-tron transfer process over nitrogen doped TiO
2nanocrystals
prepared by oxidation of titaniumnitriderdquo Journal of HazardousMaterials vol 157 no 1 pp 57ndash63 2008
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
8 International Journal of Photoenergy
400500600
700800
2
15
1
05
0
Abso
rban
ce (a
u)
Abso
rban
ce (a
u)
200 300 400 500 600 700 800Wavelength (nm)
Wavelength (nm)Calcination temp (∘C)
05
04
03
02
01
0350 400 450 500 550
NTi 2 molar ratiocalcination at different temperatures
AT ratio 2
A20T4A20T5A20T6A20T7A20T8
P25
(a)
2
15
1
05
0
Abso
rban
ce (a
u)
200 300 400 500 600 700 800Wavelength (nm)
Abso
rban
ce (a
u)
Wavelength (nm)
04
04
03
03
02
02
01
01380 400 420 440 460 480 500 520 540
Calcination at 400∘C temperaturedifferent NTi molar ratios
325
215
1050P25
A00T4A05T4A10T4A15T4
A20T4A25T4A30T4
AT ratio
Calcination temperature 400∘C
(b)
Figure 6 The typical UV-vis DR spectra of N-TiO2samples (a) prepared with 20 ammoniaTTIP molar ratio and calcined at various
temperatures (b) prepared with various ammoniaTTIP molar ratios and calcined at 400∘C
to that of the TiO2(ie P25) This phenomenon should be
ascribed to either the nitrogen doping andor sensitizationby a surface-anchored group The calcination temperatureand AT ratio are the crucial factor that can further affectthe absorption as seen in Figure 6 Similar phenomenonhad been reported by previous publications [17 22ndash25] Theabsorption edges of the N-TiO
2samples show continuous
red shift as the calcination temperature changes from 400to 700∘C which can be assigned to the intrinsic band gapabsorption of TiO
2 The shift is too minor to be observed
when the calcination temperature changes from500 to 600∘Cwhich is possibly caused by the synergetic effect of the loss ofthe nitrogen and the increase of the TiO
2crystallinity during
the calcination processThe absorption threshold (120582119892) can be
determined using the onset of the absorption edges by thesection of the fitting lines on the upward and outward sectionof the spectrum (shown in the graph inserted in Figure 6)[23] Table 1 lists the determined 120582
119892(nm) and the derived
band gap energy values The band gap of N-TiO2(119864119892) was
calculated using the 119864119892= 1240120582
119892equation It also can be
seen that N-TiO2samples have two characteristic light
absorption edges One of them corresponds to the band gapof TiO
2(1205821198921= 390sim430 nm) while the other originates from
the N-induced midgap level (1205821198922= 505sim517 nm) The color
of the samples was different with calcination temperatureand AT ratio The color of N-TiO
2samples prepared with
20 AT ratio and calcinated at 400 600 and 700∘C wasvivid yellow yellow and white respectively There is no 120582
1198922
when N-TiO2calcinated above 600∘C It can be ascribed to
the amount of N dopant decreased The color of N-TiO2
prepared with 00 10 20 and 30 AT ratio and calcinatedat 400∘C was white pale yellow yellow and vivid yellow
respectively The phenomenon that the AT ratio increasesthe shifting of the spectra towards visible region was clearlyobserved (Figure 6(a)) The absorption threshold (120582
119892) was
increased with increasing AT ratio It reveals that morenitrogen doping in the matrix of TiO
2structure results in a
shift of absorbance region toward visible light wavelengthThis is possible attribute to the nitrogen incorporated intoTiO2lattice and formation of new electronic state above
valence band caused by nitrogen doping to generate a redshift
35 Analysis of Chemical State The chemical states of dopingimpurity are critical to the optical property band gap andphotocatalytic activity of nitrogen-dopedTiO
2 To investigate
the chemical states of the doping nitrogen XPS spectra wereapplied to examine three regions the Ti 2p core level near460 eV the O 1s core level near 530 eV and the N 1s core levelnear 400 eV Figure 7 shows the experimental observation ofsurface chemical composition and the electronic structuresof N-TiO
2samples using XPS XPS peaks showed that the N-
TiO2contained only Ti O N elements and a small quantity of
carbon The presence of carbon was ascribed to the residualcarbon from the precursor solution and the adventitioushydrocarbon from the XPS instrument itself In Figures 7(a)and 7(b) the binding energy (BE) peaks corresponding toN 1s core levels for N-TiO
2are observed one major peak at
400 eV The N 1s peak at 400 eV is ascribed to the presenceof the oxidized nitrogen species and the nitrogen may beincorporating into the interstitial positions of the TiO
2lattice
and to form a TindashOndashN structure [26 27] No other N 1s peakswere detected in N-TiO
2samples As shown in Figure 7 N 1s
peak at 400 eV slightly decreased with increasing calcination
International Journal of Photoenergy 9
Bind energy (eV)
Inte
nsity
(au
)800
700
600
500
400
Calcination temp (∘C)Ti-O-N
390 395 400 405 410
AT ratio 2
(a)
Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
325
2
15
1
05
0
Ti-O-N
390 395 400 405 410
AT ratio
(b)
Bind energy (eV)
Inte
nsity
(au
) 800
700
600
500
400
Calcination temp (∘C)
Ti-O
524 526 528 530 532 534 536
AT ratio 2
(c)
Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
3
25
2
15
1
05
0
Ti-O
524 526 528 530 532 534 536
AT ratio
(d)
454 456 458 460 462 464 466 468Bind energy (eV)
Inte
nsity
(au
)
4582
4581
4583
458
4583
800
700
600
500
400
Calcination temp (∘C)AT ratio 2Ti4+2p32
Ti4+2p12
(e)
454 456 458 460 462 464 466 468Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
3
25
2
15
1
05
0
Ti4+2p32
Ti4+2p12 AT ratio
(f)
Figure 7 XPS survey and core level spectra of (a)-(b) N 1s (c)-(d) Ti 2p and (e)-(f) O 1s of N-TiO2samples
temperature This is different from the N-TiO2prepared by
flame oxidation in which nitrogen partially substitutes theoxygen sites in the TiO
2[28] The preparation method plays
an important role in determining the nitrogen state in TiO2
band structure [26 29 30]Depending on the nitrogen source
and experimental conditions N species are incorporated intoTiO2in interstitial form or substitutional form [31 32] The
interstitial N-doping is favored when the doping is carriedout under oxygen-rich conditions and the substation-typeN-doping occurs under reducing conditions [31ndash33] Therefore
10 International Journal of Photoenergy
from the atomicN 1sXPS spectra the interstitial sites (400 eV)were observed under air atmosphere
The XPS spectra of Ti 2p regions are shown in Figures7(c) and 7(d) The peaks at around 4585 and 4642 eV forP25 are ascribed to Ti 2p
32and Ti 2p
12of TiO
2(data not
shown)The line separation between Ti 2p12
and Ti 2p32
was57 eV which is consistent with the standard binding energyAccording to Figure 7 all spectra of Ti 2p
12are symmetry
The spectra of Ti 2p12
are consistent of single state and thebanding energy of peaks is 4580ndash4583 eV which shows aredshift of 05 eV compared to the binding energy of Ti4+in P25 This suggests that Ti3+ was present in N-TiO
2and
the distance of peaks between Ti 2p12
and Ti 2p32
is 57ndash59 eV The 396 eV peak is assigned to the atomic b-N stateand generally proves the presence of TiAN bonds formedwhen N atoms replace the oxygen in the TiO
2crystal lattice
[30]The peak characteristic for TindashN (396 eV) is not presentindicating the absence of the TiN phase in the N-TiO
2
samples [34]The results show that the binding energies of Ti2p peaks shift to lower energieswith a negative shift ofsim05 eVfor the N-TiO
2due to the N doping [27] The lower binding
energy than a typical Ti 2p signal of Ti4+ oxidation state sug-gests that titanium cation has a considerable interaction withthe doped nitrogen and thus TiO
2lattice is modified [27
35] Nitrogen doping accompanies the formation of oxygenvacancies andor Ti3+ defects resulting in slight shifts of theTi 2p peak toward the lower binding energy [36ndash38] Hencethe red shifts of the Ti 2p peak in comparison with P25 areused to highlight the successful nitrogen doping into the TiO
2
lattice The XRD results did not indicate the formation ofTiN bondsTherefore results indicate that the titanium atombonds with oxygen but not nitrogen Thus a shift towardlower binding energy of Ti 2p and the binding energy of N1s upon nitrogen addition indicate that the nitrogen can beindeed incorporated into the interstitial positions of TiO
2
lattice and the formation of TindashOndashN bonding by partiallyinterstitial with a carbon atom
The incorporation of nitrogen into the oxide latticeshould influence the BE of O 1s as wellTheXPS spectra of theO 1s core level consists of the one peak (Figures 3(e) and 3(f))at around 5293ndash5295 eV which is ascribed to TindashO bondin the TiO
2lattice [30] The O 1s core level moved toward
lower energy state from 5296 eV in P25 to 5294 eV in N-TiO2prepared with AT ratio 30 and calcined at 400∘C The
peak shifts by sim02 eV which might be related to the creationof oxygen vacancies as a result of the nitrogen doping Theshifting of bind energy in both N 1s and O 1s region indicatesthat nitrogen was incorporated into the lattice The shifts ofTi 2p32
and O 1s peaks are due to the introduction of oxygenvacancies into the TiO
2lattice [32] The presence of nitrogen
dopant facilitates the formation of oxygen vacancies Theaforementioned results clearly indicate that nitrogen dopingis accompanied by oxygen vacancy formation The opticaltransitions between the dopant and dopant-induced level andTi3d orbital explain the observed visible light absorptions ofN-TiO
2nanomaterials The observed two absorbance edge
features in the UV-vis spectra are directly related to the abovemodification of the electronic states from the dopants
50
40
30
20
10
00 05 1 15 2 25 3
AmmoniaTTIP molar ratio
Rem
oval
effici
ency
()
Calcination temp
400∘C
500∘C
800∘C
Figure 8 The removal efficiency of ethylene photooxidation overN-TiO
2as function of the various ammoniaTTIP molar ratios
Experimental conditions [C2H4] = 200 ppmv [H
2O]= 25060 ppmv
[O2] = 21 light intensity = 16mWcm2 temp = 30∘C reaction time
= 3 h
36 Visible Light Photocatalytic Activity To explore the pho-tocatalytic activity of different N-doped TiO
2at different
calcination temperatures and AT ratios the degradationof ethylene under visible light with a cut-off wavelengthof 400 nm was investigated Carbon dioxide started beingformed immediately after the visible light was turned on andethylene was almost totally converted to CO
2in all mea-
surements It is obviously that the N-TiO2shows significant
progress in the photodegradation of ethylene compared toP25 in visible light system P25 has no obvious photocatalyticactivity (less than 1) under visible light irradiation Resultssuggest modification of TiO
2provides visible-light-sensitive
photocatalyst which can be applied to the photooxidationof ethylene gas as the band gap of TiO
2was modified by
nitrogen doping evidenced by XPS and UV-visible DRSresults Figure 8 shows the activity of N-TiO
2catalysts in the
presence of visible light for photodegradation of ethyleneThe reaction rate increases with the increase in the AT ratiofrom 05 to 20 and then decreases in AT ratio from 20to 30 The enhancement of photocatalytic activity can beascribed to an obvious improvement in anatase crystallinityand larger surface area For the sample prepared with ATratio 20 and 30 however the removal efficiency decreasedrapidly which can be due to its less surface area Thephotocatalytic ability of N-TiO
2samples calcinated at 400
500 and 800∘C is also examined It was found that thephotocatalytic activity decreased with increasing calcinationtemperature The enhancement of photocatalytic activitycan be ascribed to an obvious improvement in anatasecrystallinity at 400∘C calcination temperature Good anatasecrystallization is beneficial for reducing the recombinationrate of the photogenerated electrons and holes due to thedecrease in the number of the defects [39] Zhao and Yangshowed that for photocatalytic oxidation application anataseis superior to rutile (a) the conduction band location foranatase is more favorable for driving conjugate reactions
International Journal of Photoenergy 11
32 eVCO2 + H2O
IntermediatesH2O
OH∙ C2H4
eminuseminusTiIII OH
TiIV OH
TiIV OH
O2
∙O2minus
∙HOO H2O2
TiIV OH+∙
CB
VBh+ NS
OV
Figure 9 Schematic diagram for the process in the photooxidation of ethylene and electron transfer process over N-TiO2under visible light
illumination
involving electrons and (b) very stable surface peroxidegroups can be formed at the anatase during photo-oxidationreaction but not on the rutile surface [40] For the samplecalcined at 800∘C the removal efficiency decreased rapidlywhich can be due to its fewer amounts of anatase andsmall 119878BET The result indicates that higher specific surfacearea smaller crystallite size and good anatase crystallizationwill promote the photocatalytic activity in visible light Theresults indicate the N-TiO
2catalyst prepared with AT ratio
20 and calcinated at 400∘C shows the best photocatalyticability
37 The Formation Mechanism of N-Doped TiO2 For the
pure TiO2 the energy of the visible light is not sufficient
to excite electrons from the valence band (VB) as theintrinsic band gap of pure TiO
2 Based on the results of UV-
vis DRS XRD and XPS the nitrogen atoms were weavedinto the crystal structure of TiO
2with structure as TindashOndash
N N-TiO2was active in the visible light irradiation for
the degradation of ethylene The following explanation forthe photocatalytic activity of N-TiO
2in the visible light
spectra can be consideredThe nitrogen existing at interstitialpositions of TiO
2lattice induces localized occupied states and
forms midband gap leading to the red shift of absorptionedge and photocatalytic activity under visible light irradiation[41] The electron (eminus) can be excited from the N-impuritylevel to the conduction band (CB) The exited electrons aretrapped by O
2adsorbed on the catalyst surface producing
O2
minus∙ superoxide anion radicals After a series of reactions(1)ndash(12) ethylene molecules are finally mineralized into CO
2
DFT calcinations and experimental results indicate that N-doping favored the formation of O vacancy (subband levelO119907) which was below the bottom of the conduction band
[42ndash47] Therefore the electrons (eminus) are excited from theN-impurity level bond to the subband level (O
119907) and then
recombine with the hole (h+) as proved in Figure 9 Theholes and electrons react with OHminus and O
2molecules on the
catalyst surface to form ∙OH radicals and O2
minus∙ superoxideanion radicals respectivelyThe protonation yields theHOO∙radicals which after trapping electrons combine to produceH2O2 The O
2
minus∙ radicals then interact with H2O adsorbed to
produce more ∙OH radicals These ∙OH radicals then reactwith gaseous ethylene and mineralize it
TiO2
h120592997888997888997888997888997888rarr h+ + eminus (1)
SndashH2O + h+ 997888rarr SndashOH∙ +H+ (2)
SndashOHminus + h+ larrrarr SndashOH∙ (3)
S1015840ndashO2+ eminus 997888rarr S1015840ndashO
2
minus∙ (4)
SndashOH + S1015840ndashO2
minus∙997888rarr SndashHO
2
∙+ S1015840ndashOminus∙ (5)
S1015840ndashO2997888rarr 2S1015840ndashO (6)
S1015840ndashO + eminus 997888rarr S1015840ndashOminus∙ (7)
SndashH2O + S1015840ndashOminus∙ 997888rarr SndashOH∙ + SndashOHminus (8)
SndashHO2
∙+ SndashHO
2
∙997888rarr SndashH
2O2+O2
(9)
SndashH2O2997888rarr 2SndashOH∙ (10)
SndashC2H4+ SndashOH∙ larrrarr SndashC
2H4OH (11)
SndashC2H4OH + S1015840ndashO
2997888rarr intermediates 997888rarr CO
2+H2O(12)
4 Conclusions
The observed changes in the UV-vis DRS XRD and XPSspectra are providing consistent structural information forTindashOndashN formation that is the nitrogen can be incorporatedinto the interstitial positions of TiO
2lattice which leads to
the enhanced photocatalytic activity in N-TiO2samples It
is concluded that the photocatalytic oxidation reactivity ofN-TiO
2under visible light illumination is mainly due to the
presence of localized occupied states caused by interstitialnitrogen and the electronhole pairs generated under visiblelight irradiation It has been found that N dopant retardedthe anatase to rutile phase transformation by forming TindashOndashN incorporated into the interstitial position of TiO
2lattice
Moreover the transformation temperatures of anatase-to-rutile progressively slightly increase when N dopant contentis increased The photocatalyst N-TiO
2prepared with AT
ratio 20 and calcinated at 400∘C shows the highest photo-catalytic activity in the oxidation of ethylene This N-TiO
2
provides an effective visible-light-responsive photocatalystfor future industrial applications in pollution control
12 International Journal of Photoenergy
Acknowledgment
This research was financially supported by the NationalScience Council of Taiwan ROC under Grant nos NSC-100-2221-E-005-007 and NSC-100-2120-M-005-002
References
[1] T Horikawa M Katoh and T Tomida ldquoPreparation and char-acterization of nitrogen-doped mesoporous titania with highspecific surface areardquo Microporous and Mesoporous Materialsvol 110 no 2-3 pp 397ndash404 2008
[2] K Yang Y Dai and B Huang ldquoStudy of the nitrogen concen-tration influence onN-dopedTiO
2anatase fromfirst-principles
calculationsrdquo Journal of Physical Chemistry C vol 111 no 32 pp12086ndash12090 2007
[3] K Pomoni A Vomvas and C Trapalis ldquoDark conductivity andtransient photoconductivity of nanocrystalline undoped andN-doped TiO
2sol-gel thin filmsrdquoThin Solid Films vol 516 no 6
pp 1271ndash1278 2008[4] S Sato ldquoPhotocatalytic activity of NO
119909-doped TiO
2in the
visible light regionrdquo Chemical Physics Letters vol 123 no 1-2pp 126ndash128 1986
[5] R Asahi T Morikawa T Ohwaki K Aoki and Y TagaldquoVisible-light photocatalysis in nitrogen-doped titaniumoxidesrdquo Science vol 293 no 5528 pp 269ndash271 2001
[6] J Ananpattarachai P Kajitvichyanukul and S Seraphin ldquoVisi-ble light absorption ability and photocatalytic oxidation activityof various interstitial N-doped TiO
2prepared from different
nitrogen dopantsrdquo Journal of Hazardous Materials vol 168 no1 pp 253ndash261 2009
[7] Y T Lin C HWeng and TW Tzeng ldquoPhotocatalysis and cat-alytic properties of nano-sized N-TiO
2catalyst synthesized by
Sol-gel methodsrdquo Journal of Advanced Oxidation Technologiesvol 13 no 3 pp 297ndash304 2010
[8] B Kosowska S Mozia A W Morawski B Grzmil M Janusand K Kałucki ldquoThe preparation of TiO
2-nitrogen doped by
calcination of TiO2sdot xH2O under ammonia atmosphere for
visible light photocatalysisrdquo Solar Energy Materials and SolarCells vol 88 no 3 pp 269ndash280 2005
[9] F Peng L Cai L Huang H Yu and H Wang ldquoPreparationof nitrogen-doped titanium dioxide with visible-light photocat-alytic activity using a facile hydrothermal methodrdquo Journal ofPhysics and Chemistry of Solids vol 69 no 7 pp 1657ndash16642008
[10] H Yu X Zheng Z Yin F Tag B Fang and K HouldquoPreparation of nitrogen-doped TiO
2nanoparticle catalyst and
its catalytic activity under visible lightrdquo Chinese Journal ofChemical Engineering vol 15 no 6 pp 802ndash807 2007
[11] Z Wang W Cai X Hong X Zhao F Xu and C CaildquoPhotocatalytic degradation of phenol in aqueous nitrogen-doped TiO
2suspensions with various light sourcesrdquo Applied
Catalysis B vol 57 no 3 pp 223ndash231 2005[12] A Trenczek-Zajac K Kowalski K Zakrzewska and M
Radecka ldquoNitrogen-doped titanium dioxidemdashcharacterizationof structural and optical propertiesrdquoMaterials ResearchBulletinvol 44 no 7 pp 1547ndash1552 2009
[13] J S Jang H G Kim S M Ji et al ldquoFormation of crystallineTiO2minus119909
N119909and its photocatalytic activityrdquo Journal of Solid State
Chemistry vol 179 no 4 pp 1067ndash1075 2006[14] H L Qin G B Gu and S Liu ldquoPreparation of nitrogen-doped
titania using sol-gel technique and its photocatalytic activityrdquo
Materials Chemistry and Physics vol 112 no 2 pp 346ndash3522008
[15] J Xu Y Ao D Fu andC Yuan J ldquoLow-temperature preparationof anatase titania-coated magnetiterdquo Journal of Physics andChemistry of Solids vol 69 pp 1980ndash1984 2008
[16] DWuM LongW Cai C Chen and YWu ldquoLow temperaturehydrothermal synthesis of N-doped TiO
2photocatalyst with
high visible-light activityrdquo Journal of Alloys andCompounds vol502 no 2 pp 289ndash294 2010
[17] K M Parida and B Naik ldquoSynthesis of mesoporous TiO2minus119909
N119909
spheres by template free homogeneous co-precipitationmethodand their photo-catalytic activity under visible light illumina-tionrdquo Journal of Colloid and Interface Science vol 333 no 1 pp269ndash276 2009
[18] N R Neti R Misra P K Bera R Dhodapkar S Bakardjievaand Z Bastl ldquoSynthesis of c-doped TiO
2nanoparticles by no-
vel sol-gel polycondensation of resorcinol with formaldehydefor visible-light photocatalysisrdquo Synthesis and Reactivity inInorganic Metal-Organic and Nano-Metal Chemistry vol 40no 5 pp 328ndash332 2010
[19] K Bubacz J Choina D Dolat E Borowiak-Palen D Mos-zynski and A W Morawski ldquoStudies on nitrogen modifiedTiO2photocatalyst prepared in different conditionsrdquoMaterials
Research Bulletin vol 45 no 9 pp 1085ndash1091 2010[20] Z Zhang X Wang J Long Q Gu Z Ding and X Fu
ldquoNitrogen-doped titanium dioxide visible light photocatalystspectroscopic identification of photoactive centersrdquo Journal ofCatalysis vol 276 pp 201ndash214 2010
[21] X Z Bu G K Zhang Y Y Gao and Y Q Yang ldquoPrepara-tion and photocatalytic properties of visible light responsiveN-doped TiO
2rectorite compositesrdquo Microporous and Meso-
porous Materials vol 136 no 1ndash3 pp 132ndash137 2010[22] C Liu X Tang C Mo and Z Qiang ldquoCharacterization and
activity of visible-light-driven TiO2photocatalyst codopedwith
nitrogen and ceriumrdquo Journal of Solid State Chemistry vol 181no 4 pp 913ndash919 2008
[23] R Kun S Tarjan AOszko et al ldquoPreparation and characteriza-tion of mesoporous N-doped and sulfuric acid treated anataseTiO2catalysts and their photocatalytic activity under UV and
Vis illuminationrdquo Journal of Solid State Chemistry vol 182 pp3076ndash3084 2009
[24] Z Pap L Baia K Mogyorosi A Dombi A Oszko and VDanciu ldquoCorrelating the visible light photoactivity of N-dopedTiO2with brookite particle size and bridged-nitro surface
speciesrdquo Catalysis Communications vol 17 pp 1ndash7 2012[25] X Z Bu G K Zhang and CH Zhang ldquoEffect of nitrogen dop-
ing on anatase-rutile phase transformation of TiO2rdquo Applied
Surface Science vol 258 pp 7997ndash8001 2012[26] Y P Peng E Yassitepe Y T Yeh I Ruzybayev S I Shah and C
P Huang ldquoPhotoelectrochemical degradation of azo dye overpulsed laser deposited nitrogen-doped TiO
2thin filmrdquo Applied
Catalysis B vol 125 pp 465ndash472 2012[27] H Jie H B Lee K H Chae et al ldquoNitrogen-doped
TiO2nanopowders prepared by chemical vapor synthesis
band structure and photocatalytic activity under visible lightrdquoResearch on Chemical Intermediates vol 38 no 6 pp 1171ndash11802012
[28] S U M Khan M Al-Shahry and W B Ingler ldquoEfficientphotochemical water splitting by a chemically modified n-TiO2rdquo Science vol 297 no 5590 pp 2243ndash2245 2002
International Journal of Photoenergy 13
[29] X X Wang S Meng X L Zhang H T Wang W Zhong andQ G Du ldquoMulti-type carbon doping of TiO
2photocatalystrdquo
Chemical Physics Letters vol 444 pp 292ndash296 2007[30] N R Khalid E Ahmed Z L Hong Y W Zhang and
M Ahmad ldquoNitrogen doped TiO2nanoparticles decorated
on graphene sheets for photocatalysis applicationsrdquo CurrentApplied Physics vol 12 no 6 pp 1485ndash1492 2012
[31] Q J Xiang J G Yu and M Jaroniec ldquoNitrogen and sulfurco-doped TiO
2nanosheets with exposed 001 facets synthesis
characterization and visible-light photocatalytic activityrdquo Phys-ical Chemistry Chemical Physics vol 13 no 11 pp 4853ndash48612011
[32] J Wang D N Tafen J P Lewis et al ldquoOrigin of photocatalyticactivity of nitrogen-doped TiO
2nanobeltsrdquo Journal of the
American Chemical Society vol 131 pp 12290ndash12297 2009[33] Q Xiang J YuWWang andM Jaroniec ldquoNitrogen self-doped
nanosized TiO2sheets with exposed 001 facets for enhanced
visible-light photocatalytic activityrdquoChemical Communicationsvol 47 no 24 pp 6906ndash6908 2011
[34] Y C Tang X H Huang H Q Yu and L H Tang ldquoNitrogen-doped TiO
2photocatalyst prepared by mechanochemical
method doping mechanisms and visible photoactivity of pol-lutant degradationrdquo International Journal of Photoenergy vol2012 Article ID 960726 10 pages 2012
[35] D E Gu Y Lu B C Yang and Y D Hu ldquoFacile preparationof micro-mesoporous carbon-doped TiO
2photocatalysts with
anatase crystalline walls under template-free conditionrdquo Chem-ical Communications no 21 pp 2453ndash2455 2008
[36] W Ren Z Ai F Jia L Zhang X Fan and Z Zou ldquoLow tem-perature preparation and visible light photocatalytic activity ofmesoporous carbon-doped crystalline TiO
2rdquo Applied Catalysis
B vol 69 no 3-4 pp 138ndash144 2007[37] EM Rockafellow X Fang B G Trewyn K Schmidt-Rohr and
W S Jenks ldquoSolid-state 13C NMR characterization of carbon-modified TiO
2rdquo Chemistry of Materials vol 21 no 7 pp 1187ndash
1197 2009[38] Y Zhang P Xiao X Zhou D Liu B B Garcia and G Cao
ldquoCarbon monoxide annealed TiO2nanotube array electrodes
for efficient biosensor applicationsrdquo Journal of Materials Chem-istry vol 19 no 7 pp 948ndash953 2009
[39] J Yu L Zhang B Cheng andY Su ldquoHydrothermal preparationand photocatalytic activity of hierarchically sponge-like macro-mesoporous Titaniardquo Journal of Physical Chemistry C vol 111no 28 pp 10582ndash10589 2007
[40] J Zhao and X Yang ldquoPhotocatalytic oxidation for indoor airpurification a literature reviewrdquo Building and Environment vol38 no 5 pp 645ndash654 2003
[41] C Di Valentin G Pacchioni and A Selloni ldquoOrigin of thedifferent photoactivity of N-doped anatase and rutile TiO
2rdquo
Physical ReviewB vol 70 no 8 Article ID 085116 4 pages 2004[42] S Livraghi M C Paganini E Giamello A Selloni C
Di Valentin and G Pacchioni ldquoOrigin of photoactivity ofnitrogen-doped titanium dioxide under visible lightrdquo Journal ofthe American Chemical Society vol 128 no 49 pp 15666ndash156712006
[43] X Chen and C Burda ldquoThe electronic origin of the visible-lightabsorption properties of C- N- and S-doped TiO
2nanomateri-
alsrdquo Journal of the American Chemical Society vol 130 no 15pp 5018ndash5019 2008
[44] C Di Valentin G Pacchioni and A Selloni ldquoTheory of carbondoping of titanium dioxiderdquo Chemistry of Materials vol 17 no26 pp 6656ndash6665 2005
[45] HWang and J P Lewis ldquoEffects of dopant states on photoactiv-ity in carbon-dopedTiO
2rdquo Journal of Physics CondensedMatter
vol 17 no 21 pp L209ndashL213 2005[46] H Li D Wang H Fan P Wang T Jiang and T Xie ldquoSynthesis
of highly efficient C-doped TiO2photocatalyst and its photo-
generated charge-transfer propertiesrdquo Journal of Colloid andInterface Science vol 354 no 1 pp 175ndash180 2011
[47] ZWu FDongWZhao and SGuo ldquoVisible light induced elec-tron transfer process over nitrogen doped TiO
2nanocrystals
prepared by oxidation of titaniumnitriderdquo Journal of HazardousMaterials vol 157 no 1 pp 57ndash63 2008
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
International Journal of Photoenergy 9
Bind energy (eV)
Inte
nsity
(au
)800
700
600
500
400
Calcination temp (∘C)Ti-O-N
390 395 400 405 410
AT ratio 2
(a)
Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
325
2
15
1
05
0
Ti-O-N
390 395 400 405 410
AT ratio
(b)
Bind energy (eV)
Inte
nsity
(au
) 800
700
600
500
400
Calcination temp (∘C)
Ti-O
524 526 528 530 532 534 536
AT ratio 2
(c)
Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
3
25
2
15
1
05
0
Ti-O
524 526 528 530 532 534 536
AT ratio
(d)
454 456 458 460 462 464 466 468Bind energy (eV)
Inte
nsity
(au
)
4582
4581
4583
458
4583
800
700
600
500
400
Calcination temp (∘C)AT ratio 2Ti4+2p32
Ti4+2p12
(e)
454 456 458 460 462 464 466 468Bind energy (eV)
Inte
nsity
(au
)
Calcination temp 400∘C
3
25
2
15
1
05
0
Ti4+2p32
Ti4+2p12 AT ratio
(f)
Figure 7 XPS survey and core level spectra of (a)-(b) N 1s (c)-(d) Ti 2p and (e)-(f) O 1s of N-TiO2samples
temperature This is different from the N-TiO2prepared by
flame oxidation in which nitrogen partially substitutes theoxygen sites in the TiO
2[28] The preparation method plays
an important role in determining the nitrogen state in TiO2
band structure [26 29 30]Depending on the nitrogen source
and experimental conditions N species are incorporated intoTiO2in interstitial form or substitutional form [31 32] The
interstitial N-doping is favored when the doping is carriedout under oxygen-rich conditions and the substation-typeN-doping occurs under reducing conditions [31ndash33] Therefore
10 International Journal of Photoenergy
from the atomicN 1sXPS spectra the interstitial sites (400 eV)were observed under air atmosphere
The XPS spectra of Ti 2p regions are shown in Figures7(c) and 7(d) The peaks at around 4585 and 4642 eV forP25 are ascribed to Ti 2p
32and Ti 2p
12of TiO
2(data not
shown)The line separation between Ti 2p12
and Ti 2p32
was57 eV which is consistent with the standard binding energyAccording to Figure 7 all spectra of Ti 2p
12are symmetry
The spectra of Ti 2p12
are consistent of single state and thebanding energy of peaks is 4580ndash4583 eV which shows aredshift of 05 eV compared to the binding energy of Ti4+in P25 This suggests that Ti3+ was present in N-TiO
2and
the distance of peaks between Ti 2p12
and Ti 2p32
is 57ndash59 eV The 396 eV peak is assigned to the atomic b-N stateand generally proves the presence of TiAN bonds formedwhen N atoms replace the oxygen in the TiO
2crystal lattice
[30]The peak characteristic for TindashN (396 eV) is not presentindicating the absence of the TiN phase in the N-TiO
2
samples [34]The results show that the binding energies of Ti2p peaks shift to lower energieswith a negative shift ofsim05 eVfor the N-TiO
2due to the N doping [27] The lower binding
energy than a typical Ti 2p signal of Ti4+ oxidation state sug-gests that titanium cation has a considerable interaction withthe doped nitrogen and thus TiO
2lattice is modified [27
35] Nitrogen doping accompanies the formation of oxygenvacancies andor Ti3+ defects resulting in slight shifts of theTi 2p peak toward the lower binding energy [36ndash38] Hencethe red shifts of the Ti 2p peak in comparison with P25 areused to highlight the successful nitrogen doping into the TiO
2
lattice The XRD results did not indicate the formation ofTiN bondsTherefore results indicate that the titanium atombonds with oxygen but not nitrogen Thus a shift towardlower binding energy of Ti 2p and the binding energy of N1s upon nitrogen addition indicate that the nitrogen can beindeed incorporated into the interstitial positions of TiO
2
lattice and the formation of TindashOndashN bonding by partiallyinterstitial with a carbon atom
The incorporation of nitrogen into the oxide latticeshould influence the BE of O 1s as wellTheXPS spectra of theO 1s core level consists of the one peak (Figures 3(e) and 3(f))at around 5293ndash5295 eV which is ascribed to TindashO bondin the TiO
2lattice [30] The O 1s core level moved toward
lower energy state from 5296 eV in P25 to 5294 eV in N-TiO2prepared with AT ratio 30 and calcined at 400∘C The
peak shifts by sim02 eV which might be related to the creationof oxygen vacancies as a result of the nitrogen doping Theshifting of bind energy in both N 1s and O 1s region indicatesthat nitrogen was incorporated into the lattice The shifts ofTi 2p32
and O 1s peaks are due to the introduction of oxygenvacancies into the TiO
2lattice [32] The presence of nitrogen
dopant facilitates the formation of oxygen vacancies Theaforementioned results clearly indicate that nitrogen dopingis accompanied by oxygen vacancy formation The opticaltransitions between the dopant and dopant-induced level andTi3d orbital explain the observed visible light absorptions ofN-TiO
2nanomaterials The observed two absorbance edge
features in the UV-vis spectra are directly related to the abovemodification of the electronic states from the dopants
50
40
30
20
10
00 05 1 15 2 25 3
AmmoniaTTIP molar ratio
Rem
oval
effici
ency
()
Calcination temp
400∘C
500∘C
800∘C
Figure 8 The removal efficiency of ethylene photooxidation overN-TiO
2as function of the various ammoniaTTIP molar ratios
Experimental conditions [C2H4] = 200 ppmv [H
2O]= 25060 ppmv
[O2] = 21 light intensity = 16mWcm2 temp = 30∘C reaction time
= 3 h
36 Visible Light Photocatalytic Activity To explore the pho-tocatalytic activity of different N-doped TiO
2at different
calcination temperatures and AT ratios the degradationof ethylene under visible light with a cut-off wavelengthof 400 nm was investigated Carbon dioxide started beingformed immediately after the visible light was turned on andethylene was almost totally converted to CO
2in all mea-
surements It is obviously that the N-TiO2shows significant
progress in the photodegradation of ethylene compared toP25 in visible light system P25 has no obvious photocatalyticactivity (less than 1) under visible light irradiation Resultssuggest modification of TiO
2provides visible-light-sensitive
photocatalyst which can be applied to the photooxidationof ethylene gas as the band gap of TiO
2was modified by
nitrogen doping evidenced by XPS and UV-visible DRSresults Figure 8 shows the activity of N-TiO
2catalysts in the
presence of visible light for photodegradation of ethyleneThe reaction rate increases with the increase in the AT ratiofrom 05 to 20 and then decreases in AT ratio from 20to 30 The enhancement of photocatalytic activity can beascribed to an obvious improvement in anatase crystallinityand larger surface area For the sample prepared with ATratio 20 and 30 however the removal efficiency decreasedrapidly which can be due to its less surface area Thephotocatalytic ability of N-TiO
2samples calcinated at 400
500 and 800∘C is also examined It was found that thephotocatalytic activity decreased with increasing calcinationtemperature The enhancement of photocatalytic activitycan be ascribed to an obvious improvement in anatasecrystallinity at 400∘C calcination temperature Good anatasecrystallization is beneficial for reducing the recombinationrate of the photogenerated electrons and holes due to thedecrease in the number of the defects [39] Zhao and Yangshowed that for photocatalytic oxidation application anataseis superior to rutile (a) the conduction band location foranatase is more favorable for driving conjugate reactions
International Journal of Photoenergy 11
32 eVCO2 + H2O
IntermediatesH2O
OH∙ C2H4
eminuseminusTiIII OH
TiIV OH
TiIV OH
O2
∙O2minus
∙HOO H2O2
TiIV OH+∙
CB
VBh+ NS
OV
Figure 9 Schematic diagram for the process in the photooxidation of ethylene and electron transfer process over N-TiO2under visible light
illumination
involving electrons and (b) very stable surface peroxidegroups can be formed at the anatase during photo-oxidationreaction but not on the rutile surface [40] For the samplecalcined at 800∘C the removal efficiency decreased rapidlywhich can be due to its fewer amounts of anatase andsmall 119878BET The result indicates that higher specific surfacearea smaller crystallite size and good anatase crystallizationwill promote the photocatalytic activity in visible light Theresults indicate the N-TiO
2catalyst prepared with AT ratio
20 and calcinated at 400∘C shows the best photocatalyticability
37 The Formation Mechanism of N-Doped TiO2 For the
pure TiO2 the energy of the visible light is not sufficient
to excite electrons from the valence band (VB) as theintrinsic band gap of pure TiO
2 Based on the results of UV-
vis DRS XRD and XPS the nitrogen atoms were weavedinto the crystal structure of TiO
2with structure as TindashOndash
N N-TiO2was active in the visible light irradiation for
the degradation of ethylene The following explanation forthe photocatalytic activity of N-TiO
2in the visible light
spectra can be consideredThe nitrogen existing at interstitialpositions of TiO
2lattice induces localized occupied states and
forms midband gap leading to the red shift of absorptionedge and photocatalytic activity under visible light irradiation[41] The electron (eminus) can be excited from the N-impuritylevel to the conduction band (CB) The exited electrons aretrapped by O
2adsorbed on the catalyst surface producing
O2
minus∙ superoxide anion radicals After a series of reactions(1)ndash(12) ethylene molecules are finally mineralized into CO
2
DFT calcinations and experimental results indicate that N-doping favored the formation of O vacancy (subband levelO119907) which was below the bottom of the conduction band
[42ndash47] Therefore the electrons (eminus) are excited from theN-impurity level bond to the subband level (O
119907) and then
recombine with the hole (h+) as proved in Figure 9 Theholes and electrons react with OHminus and O
2molecules on the
catalyst surface to form ∙OH radicals and O2
minus∙ superoxideanion radicals respectivelyThe protonation yields theHOO∙radicals which after trapping electrons combine to produceH2O2 The O
2
minus∙ radicals then interact with H2O adsorbed to
produce more ∙OH radicals These ∙OH radicals then reactwith gaseous ethylene and mineralize it
TiO2
h120592997888997888997888997888997888rarr h+ + eminus (1)
SndashH2O + h+ 997888rarr SndashOH∙ +H+ (2)
SndashOHminus + h+ larrrarr SndashOH∙ (3)
S1015840ndashO2+ eminus 997888rarr S1015840ndashO
2
minus∙ (4)
SndashOH + S1015840ndashO2
minus∙997888rarr SndashHO
2
∙+ S1015840ndashOminus∙ (5)
S1015840ndashO2997888rarr 2S1015840ndashO (6)
S1015840ndashO + eminus 997888rarr S1015840ndashOminus∙ (7)
SndashH2O + S1015840ndashOminus∙ 997888rarr SndashOH∙ + SndashOHminus (8)
SndashHO2
∙+ SndashHO
2
∙997888rarr SndashH
2O2+O2
(9)
SndashH2O2997888rarr 2SndashOH∙ (10)
SndashC2H4+ SndashOH∙ larrrarr SndashC
2H4OH (11)
SndashC2H4OH + S1015840ndashO
2997888rarr intermediates 997888rarr CO
2+H2O(12)
4 Conclusions
The observed changes in the UV-vis DRS XRD and XPSspectra are providing consistent structural information forTindashOndashN formation that is the nitrogen can be incorporatedinto the interstitial positions of TiO
2lattice which leads to
the enhanced photocatalytic activity in N-TiO2samples It
is concluded that the photocatalytic oxidation reactivity ofN-TiO
2under visible light illumination is mainly due to the
presence of localized occupied states caused by interstitialnitrogen and the electronhole pairs generated under visiblelight irradiation It has been found that N dopant retardedthe anatase to rutile phase transformation by forming TindashOndashN incorporated into the interstitial position of TiO
2lattice
Moreover the transformation temperatures of anatase-to-rutile progressively slightly increase when N dopant contentis increased The photocatalyst N-TiO
2prepared with AT
ratio 20 and calcinated at 400∘C shows the highest photo-catalytic activity in the oxidation of ethylene This N-TiO
2
provides an effective visible-light-responsive photocatalystfor future industrial applications in pollution control
12 International Journal of Photoenergy
Acknowledgment
This research was financially supported by the NationalScience Council of Taiwan ROC under Grant nos NSC-100-2221-E-005-007 and NSC-100-2120-M-005-002
References
[1] T Horikawa M Katoh and T Tomida ldquoPreparation and char-acterization of nitrogen-doped mesoporous titania with highspecific surface areardquo Microporous and Mesoporous Materialsvol 110 no 2-3 pp 397ndash404 2008
[2] K Yang Y Dai and B Huang ldquoStudy of the nitrogen concen-tration influence onN-dopedTiO
2anatase fromfirst-principles
calculationsrdquo Journal of Physical Chemistry C vol 111 no 32 pp12086ndash12090 2007
[3] K Pomoni A Vomvas and C Trapalis ldquoDark conductivity andtransient photoconductivity of nanocrystalline undoped andN-doped TiO
2sol-gel thin filmsrdquoThin Solid Films vol 516 no 6
pp 1271ndash1278 2008[4] S Sato ldquoPhotocatalytic activity of NO
119909-doped TiO
2in the
visible light regionrdquo Chemical Physics Letters vol 123 no 1-2pp 126ndash128 1986
[5] R Asahi T Morikawa T Ohwaki K Aoki and Y TagaldquoVisible-light photocatalysis in nitrogen-doped titaniumoxidesrdquo Science vol 293 no 5528 pp 269ndash271 2001
[6] J Ananpattarachai P Kajitvichyanukul and S Seraphin ldquoVisi-ble light absorption ability and photocatalytic oxidation activityof various interstitial N-doped TiO
2prepared from different
nitrogen dopantsrdquo Journal of Hazardous Materials vol 168 no1 pp 253ndash261 2009
[7] Y T Lin C HWeng and TW Tzeng ldquoPhotocatalysis and cat-alytic properties of nano-sized N-TiO
2catalyst synthesized by
Sol-gel methodsrdquo Journal of Advanced Oxidation Technologiesvol 13 no 3 pp 297ndash304 2010
[8] B Kosowska S Mozia A W Morawski B Grzmil M Janusand K Kałucki ldquoThe preparation of TiO
2-nitrogen doped by
calcination of TiO2sdot xH2O under ammonia atmosphere for
visible light photocatalysisrdquo Solar Energy Materials and SolarCells vol 88 no 3 pp 269ndash280 2005
[9] F Peng L Cai L Huang H Yu and H Wang ldquoPreparationof nitrogen-doped titanium dioxide with visible-light photocat-alytic activity using a facile hydrothermal methodrdquo Journal ofPhysics and Chemistry of Solids vol 69 no 7 pp 1657ndash16642008
[10] H Yu X Zheng Z Yin F Tag B Fang and K HouldquoPreparation of nitrogen-doped TiO
2nanoparticle catalyst and
its catalytic activity under visible lightrdquo Chinese Journal ofChemical Engineering vol 15 no 6 pp 802ndash807 2007
[11] Z Wang W Cai X Hong X Zhao F Xu and C CaildquoPhotocatalytic degradation of phenol in aqueous nitrogen-doped TiO
2suspensions with various light sourcesrdquo Applied
Catalysis B vol 57 no 3 pp 223ndash231 2005[12] A Trenczek-Zajac K Kowalski K Zakrzewska and M
Radecka ldquoNitrogen-doped titanium dioxidemdashcharacterizationof structural and optical propertiesrdquoMaterials ResearchBulletinvol 44 no 7 pp 1547ndash1552 2009
[13] J S Jang H G Kim S M Ji et al ldquoFormation of crystallineTiO2minus119909
N119909and its photocatalytic activityrdquo Journal of Solid State
Chemistry vol 179 no 4 pp 1067ndash1075 2006[14] H L Qin G B Gu and S Liu ldquoPreparation of nitrogen-doped
titania using sol-gel technique and its photocatalytic activityrdquo
Materials Chemistry and Physics vol 112 no 2 pp 346ndash3522008
[15] J Xu Y Ao D Fu andC Yuan J ldquoLow-temperature preparationof anatase titania-coated magnetiterdquo Journal of Physics andChemistry of Solids vol 69 pp 1980ndash1984 2008
[16] DWuM LongW Cai C Chen and YWu ldquoLow temperaturehydrothermal synthesis of N-doped TiO
2photocatalyst with
high visible-light activityrdquo Journal of Alloys andCompounds vol502 no 2 pp 289ndash294 2010
[17] K M Parida and B Naik ldquoSynthesis of mesoporous TiO2minus119909
N119909
spheres by template free homogeneous co-precipitationmethodand their photo-catalytic activity under visible light illumina-tionrdquo Journal of Colloid and Interface Science vol 333 no 1 pp269ndash276 2009
[18] N R Neti R Misra P K Bera R Dhodapkar S Bakardjievaand Z Bastl ldquoSynthesis of c-doped TiO
2nanoparticles by no-
vel sol-gel polycondensation of resorcinol with formaldehydefor visible-light photocatalysisrdquo Synthesis and Reactivity inInorganic Metal-Organic and Nano-Metal Chemistry vol 40no 5 pp 328ndash332 2010
[19] K Bubacz J Choina D Dolat E Borowiak-Palen D Mos-zynski and A W Morawski ldquoStudies on nitrogen modifiedTiO2photocatalyst prepared in different conditionsrdquoMaterials
Research Bulletin vol 45 no 9 pp 1085ndash1091 2010[20] Z Zhang X Wang J Long Q Gu Z Ding and X Fu
ldquoNitrogen-doped titanium dioxide visible light photocatalystspectroscopic identification of photoactive centersrdquo Journal ofCatalysis vol 276 pp 201ndash214 2010
[21] X Z Bu G K Zhang Y Y Gao and Y Q Yang ldquoPrepara-tion and photocatalytic properties of visible light responsiveN-doped TiO
2rectorite compositesrdquo Microporous and Meso-
porous Materials vol 136 no 1ndash3 pp 132ndash137 2010[22] C Liu X Tang C Mo and Z Qiang ldquoCharacterization and
activity of visible-light-driven TiO2photocatalyst codopedwith
nitrogen and ceriumrdquo Journal of Solid State Chemistry vol 181no 4 pp 913ndash919 2008
[23] R Kun S Tarjan AOszko et al ldquoPreparation and characteriza-tion of mesoporous N-doped and sulfuric acid treated anataseTiO2catalysts and their photocatalytic activity under UV and
Vis illuminationrdquo Journal of Solid State Chemistry vol 182 pp3076ndash3084 2009
[24] Z Pap L Baia K Mogyorosi A Dombi A Oszko and VDanciu ldquoCorrelating the visible light photoactivity of N-dopedTiO2with brookite particle size and bridged-nitro surface
speciesrdquo Catalysis Communications vol 17 pp 1ndash7 2012[25] X Z Bu G K Zhang and CH Zhang ldquoEffect of nitrogen dop-
ing on anatase-rutile phase transformation of TiO2rdquo Applied
Surface Science vol 258 pp 7997ndash8001 2012[26] Y P Peng E Yassitepe Y T Yeh I Ruzybayev S I Shah and C
P Huang ldquoPhotoelectrochemical degradation of azo dye overpulsed laser deposited nitrogen-doped TiO
2thin filmrdquo Applied
Catalysis B vol 125 pp 465ndash472 2012[27] H Jie H B Lee K H Chae et al ldquoNitrogen-doped
TiO2nanopowders prepared by chemical vapor synthesis
band structure and photocatalytic activity under visible lightrdquoResearch on Chemical Intermediates vol 38 no 6 pp 1171ndash11802012
[28] S U M Khan M Al-Shahry and W B Ingler ldquoEfficientphotochemical water splitting by a chemically modified n-TiO2rdquo Science vol 297 no 5590 pp 2243ndash2245 2002
International Journal of Photoenergy 13
[29] X X Wang S Meng X L Zhang H T Wang W Zhong andQ G Du ldquoMulti-type carbon doping of TiO
2photocatalystrdquo
Chemical Physics Letters vol 444 pp 292ndash296 2007[30] N R Khalid E Ahmed Z L Hong Y W Zhang and
M Ahmad ldquoNitrogen doped TiO2nanoparticles decorated
on graphene sheets for photocatalysis applicationsrdquo CurrentApplied Physics vol 12 no 6 pp 1485ndash1492 2012
[31] Q J Xiang J G Yu and M Jaroniec ldquoNitrogen and sulfurco-doped TiO
2nanosheets with exposed 001 facets synthesis
characterization and visible-light photocatalytic activityrdquo Phys-ical Chemistry Chemical Physics vol 13 no 11 pp 4853ndash48612011
[32] J Wang D N Tafen J P Lewis et al ldquoOrigin of photocatalyticactivity of nitrogen-doped TiO
2nanobeltsrdquo Journal of the
American Chemical Society vol 131 pp 12290ndash12297 2009[33] Q Xiang J YuWWang andM Jaroniec ldquoNitrogen self-doped
nanosized TiO2sheets with exposed 001 facets for enhanced
visible-light photocatalytic activityrdquoChemical Communicationsvol 47 no 24 pp 6906ndash6908 2011
[34] Y C Tang X H Huang H Q Yu and L H Tang ldquoNitrogen-doped TiO
2photocatalyst prepared by mechanochemical
method doping mechanisms and visible photoactivity of pol-lutant degradationrdquo International Journal of Photoenergy vol2012 Article ID 960726 10 pages 2012
[35] D E Gu Y Lu B C Yang and Y D Hu ldquoFacile preparationof micro-mesoporous carbon-doped TiO
2photocatalysts with
anatase crystalline walls under template-free conditionrdquo Chem-ical Communications no 21 pp 2453ndash2455 2008
[36] W Ren Z Ai F Jia L Zhang X Fan and Z Zou ldquoLow tem-perature preparation and visible light photocatalytic activity ofmesoporous carbon-doped crystalline TiO
2rdquo Applied Catalysis
B vol 69 no 3-4 pp 138ndash144 2007[37] EM Rockafellow X Fang B G Trewyn K Schmidt-Rohr and
W S Jenks ldquoSolid-state 13C NMR characterization of carbon-modified TiO
2rdquo Chemistry of Materials vol 21 no 7 pp 1187ndash
1197 2009[38] Y Zhang P Xiao X Zhou D Liu B B Garcia and G Cao
ldquoCarbon monoxide annealed TiO2nanotube array electrodes
for efficient biosensor applicationsrdquo Journal of Materials Chem-istry vol 19 no 7 pp 948ndash953 2009
[39] J Yu L Zhang B Cheng andY Su ldquoHydrothermal preparationand photocatalytic activity of hierarchically sponge-like macro-mesoporous Titaniardquo Journal of Physical Chemistry C vol 111no 28 pp 10582ndash10589 2007
[40] J Zhao and X Yang ldquoPhotocatalytic oxidation for indoor airpurification a literature reviewrdquo Building and Environment vol38 no 5 pp 645ndash654 2003
[41] C Di Valentin G Pacchioni and A Selloni ldquoOrigin of thedifferent photoactivity of N-doped anatase and rutile TiO
2rdquo
Physical ReviewB vol 70 no 8 Article ID 085116 4 pages 2004[42] S Livraghi M C Paganini E Giamello A Selloni C
Di Valentin and G Pacchioni ldquoOrigin of photoactivity ofnitrogen-doped titanium dioxide under visible lightrdquo Journal ofthe American Chemical Society vol 128 no 49 pp 15666ndash156712006
[43] X Chen and C Burda ldquoThe electronic origin of the visible-lightabsorption properties of C- N- and S-doped TiO
2nanomateri-
alsrdquo Journal of the American Chemical Society vol 130 no 15pp 5018ndash5019 2008
[44] C Di Valentin G Pacchioni and A Selloni ldquoTheory of carbondoping of titanium dioxiderdquo Chemistry of Materials vol 17 no26 pp 6656ndash6665 2005
[45] HWang and J P Lewis ldquoEffects of dopant states on photoactiv-ity in carbon-dopedTiO
2rdquo Journal of Physics CondensedMatter
vol 17 no 21 pp L209ndashL213 2005[46] H Li D Wang H Fan P Wang T Jiang and T Xie ldquoSynthesis
of highly efficient C-doped TiO2photocatalyst and its photo-
generated charge-transfer propertiesrdquo Journal of Colloid andInterface Science vol 354 no 1 pp 175ndash180 2011
[47] ZWu FDongWZhao and SGuo ldquoVisible light induced elec-tron transfer process over nitrogen doped TiO
2nanocrystals
prepared by oxidation of titaniumnitriderdquo Journal of HazardousMaterials vol 157 no 1 pp 57ndash63 2008
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
10 International Journal of Photoenergy
from the atomicN 1sXPS spectra the interstitial sites (400 eV)were observed under air atmosphere
The XPS spectra of Ti 2p regions are shown in Figures7(c) and 7(d) The peaks at around 4585 and 4642 eV forP25 are ascribed to Ti 2p
32and Ti 2p
12of TiO
2(data not
shown)The line separation between Ti 2p12
and Ti 2p32
was57 eV which is consistent with the standard binding energyAccording to Figure 7 all spectra of Ti 2p
12are symmetry
The spectra of Ti 2p12
are consistent of single state and thebanding energy of peaks is 4580ndash4583 eV which shows aredshift of 05 eV compared to the binding energy of Ti4+in P25 This suggests that Ti3+ was present in N-TiO
2and
the distance of peaks between Ti 2p12
and Ti 2p32
is 57ndash59 eV The 396 eV peak is assigned to the atomic b-N stateand generally proves the presence of TiAN bonds formedwhen N atoms replace the oxygen in the TiO
2crystal lattice
[30]The peak characteristic for TindashN (396 eV) is not presentindicating the absence of the TiN phase in the N-TiO
2
samples [34]The results show that the binding energies of Ti2p peaks shift to lower energieswith a negative shift ofsim05 eVfor the N-TiO
2due to the N doping [27] The lower binding
energy than a typical Ti 2p signal of Ti4+ oxidation state sug-gests that titanium cation has a considerable interaction withthe doped nitrogen and thus TiO
2lattice is modified [27
35] Nitrogen doping accompanies the formation of oxygenvacancies andor Ti3+ defects resulting in slight shifts of theTi 2p peak toward the lower binding energy [36ndash38] Hencethe red shifts of the Ti 2p peak in comparison with P25 areused to highlight the successful nitrogen doping into the TiO
2
lattice The XRD results did not indicate the formation ofTiN bondsTherefore results indicate that the titanium atombonds with oxygen but not nitrogen Thus a shift towardlower binding energy of Ti 2p and the binding energy of N1s upon nitrogen addition indicate that the nitrogen can beindeed incorporated into the interstitial positions of TiO
2
lattice and the formation of TindashOndashN bonding by partiallyinterstitial with a carbon atom
The incorporation of nitrogen into the oxide latticeshould influence the BE of O 1s as wellTheXPS spectra of theO 1s core level consists of the one peak (Figures 3(e) and 3(f))at around 5293ndash5295 eV which is ascribed to TindashO bondin the TiO
2lattice [30] The O 1s core level moved toward
lower energy state from 5296 eV in P25 to 5294 eV in N-TiO2prepared with AT ratio 30 and calcined at 400∘C The
peak shifts by sim02 eV which might be related to the creationof oxygen vacancies as a result of the nitrogen doping Theshifting of bind energy in both N 1s and O 1s region indicatesthat nitrogen was incorporated into the lattice The shifts ofTi 2p32
and O 1s peaks are due to the introduction of oxygenvacancies into the TiO
2lattice [32] The presence of nitrogen
dopant facilitates the formation of oxygen vacancies Theaforementioned results clearly indicate that nitrogen dopingis accompanied by oxygen vacancy formation The opticaltransitions between the dopant and dopant-induced level andTi3d orbital explain the observed visible light absorptions ofN-TiO
2nanomaterials The observed two absorbance edge
features in the UV-vis spectra are directly related to the abovemodification of the electronic states from the dopants
50
40
30
20
10
00 05 1 15 2 25 3
AmmoniaTTIP molar ratio
Rem
oval
effici
ency
()
Calcination temp
400∘C
500∘C
800∘C
Figure 8 The removal efficiency of ethylene photooxidation overN-TiO
2as function of the various ammoniaTTIP molar ratios
Experimental conditions [C2H4] = 200 ppmv [H
2O]= 25060 ppmv
[O2] = 21 light intensity = 16mWcm2 temp = 30∘C reaction time
= 3 h
36 Visible Light Photocatalytic Activity To explore the pho-tocatalytic activity of different N-doped TiO
2at different
calcination temperatures and AT ratios the degradationof ethylene under visible light with a cut-off wavelengthof 400 nm was investigated Carbon dioxide started beingformed immediately after the visible light was turned on andethylene was almost totally converted to CO
2in all mea-
surements It is obviously that the N-TiO2shows significant
progress in the photodegradation of ethylene compared toP25 in visible light system P25 has no obvious photocatalyticactivity (less than 1) under visible light irradiation Resultssuggest modification of TiO
2provides visible-light-sensitive
photocatalyst which can be applied to the photooxidationof ethylene gas as the band gap of TiO
2was modified by
nitrogen doping evidenced by XPS and UV-visible DRSresults Figure 8 shows the activity of N-TiO
2catalysts in the
presence of visible light for photodegradation of ethyleneThe reaction rate increases with the increase in the AT ratiofrom 05 to 20 and then decreases in AT ratio from 20to 30 The enhancement of photocatalytic activity can beascribed to an obvious improvement in anatase crystallinityand larger surface area For the sample prepared with ATratio 20 and 30 however the removal efficiency decreasedrapidly which can be due to its less surface area Thephotocatalytic ability of N-TiO
2samples calcinated at 400
500 and 800∘C is also examined It was found that thephotocatalytic activity decreased with increasing calcinationtemperature The enhancement of photocatalytic activitycan be ascribed to an obvious improvement in anatasecrystallinity at 400∘C calcination temperature Good anatasecrystallization is beneficial for reducing the recombinationrate of the photogenerated electrons and holes due to thedecrease in the number of the defects [39] Zhao and Yangshowed that for photocatalytic oxidation application anataseis superior to rutile (a) the conduction band location foranatase is more favorable for driving conjugate reactions
International Journal of Photoenergy 11
32 eVCO2 + H2O
IntermediatesH2O
OH∙ C2H4
eminuseminusTiIII OH
TiIV OH
TiIV OH
O2
∙O2minus
∙HOO H2O2
TiIV OH+∙
CB
VBh+ NS
OV
Figure 9 Schematic diagram for the process in the photooxidation of ethylene and electron transfer process over N-TiO2under visible light
illumination
involving electrons and (b) very stable surface peroxidegroups can be formed at the anatase during photo-oxidationreaction but not on the rutile surface [40] For the samplecalcined at 800∘C the removal efficiency decreased rapidlywhich can be due to its fewer amounts of anatase andsmall 119878BET The result indicates that higher specific surfacearea smaller crystallite size and good anatase crystallizationwill promote the photocatalytic activity in visible light Theresults indicate the N-TiO
2catalyst prepared with AT ratio
20 and calcinated at 400∘C shows the best photocatalyticability
37 The Formation Mechanism of N-Doped TiO2 For the
pure TiO2 the energy of the visible light is not sufficient
to excite electrons from the valence band (VB) as theintrinsic band gap of pure TiO
2 Based on the results of UV-
vis DRS XRD and XPS the nitrogen atoms were weavedinto the crystal structure of TiO
2with structure as TindashOndash
N N-TiO2was active in the visible light irradiation for
the degradation of ethylene The following explanation forthe photocatalytic activity of N-TiO
2in the visible light
spectra can be consideredThe nitrogen existing at interstitialpositions of TiO
2lattice induces localized occupied states and
forms midband gap leading to the red shift of absorptionedge and photocatalytic activity under visible light irradiation[41] The electron (eminus) can be excited from the N-impuritylevel to the conduction band (CB) The exited electrons aretrapped by O
2adsorbed on the catalyst surface producing
O2
minus∙ superoxide anion radicals After a series of reactions(1)ndash(12) ethylene molecules are finally mineralized into CO
2
DFT calcinations and experimental results indicate that N-doping favored the formation of O vacancy (subband levelO119907) which was below the bottom of the conduction band
[42ndash47] Therefore the electrons (eminus) are excited from theN-impurity level bond to the subband level (O
119907) and then
recombine with the hole (h+) as proved in Figure 9 Theholes and electrons react with OHminus and O
2molecules on the
catalyst surface to form ∙OH radicals and O2
minus∙ superoxideanion radicals respectivelyThe protonation yields theHOO∙radicals which after trapping electrons combine to produceH2O2 The O
2
minus∙ radicals then interact with H2O adsorbed to
produce more ∙OH radicals These ∙OH radicals then reactwith gaseous ethylene and mineralize it
TiO2
h120592997888997888997888997888997888rarr h+ + eminus (1)
SndashH2O + h+ 997888rarr SndashOH∙ +H+ (2)
SndashOHminus + h+ larrrarr SndashOH∙ (3)
S1015840ndashO2+ eminus 997888rarr S1015840ndashO
2
minus∙ (4)
SndashOH + S1015840ndashO2
minus∙997888rarr SndashHO
2
∙+ S1015840ndashOminus∙ (5)
S1015840ndashO2997888rarr 2S1015840ndashO (6)
S1015840ndashO + eminus 997888rarr S1015840ndashOminus∙ (7)
SndashH2O + S1015840ndashOminus∙ 997888rarr SndashOH∙ + SndashOHminus (8)
SndashHO2
∙+ SndashHO
2
∙997888rarr SndashH
2O2+O2
(9)
SndashH2O2997888rarr 2SndashOH∙ (10)
SndashC2H4+ SndashOH∙ larrrarr SndashC
2H4OH (11)
SndashC2H4OH + S1015840ndashO
2997888rarr intermediates 997888rarr CO
2+H2O(12)
4 Conclusions
The observed changes in the UV-vis DRS XRD and XPSspectra are providing consistent structural information forTindashOndashN formation that is the nitrogen can be incorporatedinto the interstitial positions of TiO
2lattice which leads to
the enhanced photocatalytic activity in N-TiO2samples It
is concluded that the photocatalytic oxidation reactivity ofN-TiO
2under visible light illumination is mainly due to the
presence of localized occupied states caused by interstitialnitrogen and the electronhole pairs generated under visiblelight irradiation It has been found that N dopant retardedthe anatase to rutile phase transformation by forming TindashOndashN incorporated into the interstitial position of TiO
2lattice
Moreover the transformation temperatures of anatase-to-rutile progressively slightly increase when N dopant contentis increased The photocatalyst N-TiO
2prepared with AT
ratio 20 and calcinated at 400∘C shows the highest photo-catalytic activity in the oxidation of ethylene This N-TiO
2
provides an effective visible-light-responsive photocatalystfor future industrial applications in pollution control
12 International Journal of Photoenergy
Acknowledgment
This research was financially supported by the NationalScience Council of Taiwan ROC under Grant nos NSC-100-2221-E-005-007 and NSC-100-2120-M-005-002
References
[1] T Horikawa M Katoh and T Tomida ldquoPreparation and char-acterization of nitrogen-doped mesoporous titania with highspecific surface areardquo Microporous and Mesoporous Materialsvol 110 no 2-3 pp 397ndash404 2008
[2] K Yang Y Dai and B Huang ldquoStudy of the nitrogen concen-tration influence onN-dopedTiO
2anatase fromfirst-principles
calculationsrdquo Journal of Physical Chemistry C vol 111 no 32 pp12086ndash12090 2007
[3] K Pomoni A Vomvas and C Trapalis ldquoDark conductivity andtransient photoconductivity of nanocrystalline undoped andN-doped TiO
2sol-gel thin filmsrdquoThin Solid Films vol 516 no 6
pp 1271ndash1278 2008[4] S Sato ldquoPhotocatalytic activity of NO
119909-doped TiO
2in the
visible light regionrdquo Chemical Physics Letters vol 123 no 1-2pp 126ndash128 1986
[5] R Asahi T Morikawa T Ohwaki K Aoki and Y TagaldquoVisible-light photocatalysis in nitrogen-doped titaniumoxidesrdquo Science vol 293 no 5528 pp 269ndash271 2001
[6] J Ananpattarachai P Kajitvichyanukul and S Seraphin ldquoVisi-ble light absorption ability and photocatalytic oxidation activityof various interstitial N-doped TiO
2prepared from different
nitrogen dopantsrdquo Journal of Hazardous Materials vol 168 no1 pp 253ndash261 2009
[7] Y T Lin C HWeng and TW Tzeng ldquoPhotocatalysis and cat-alytic properties of nano-sized N-TiO
2catalyst synthesized by
Sol-gel methodsrdquo Journal of Advanced Oxidation Technologiesvol 13 no 3 pp 297ndash304 2010
[8] B Kosowska S Mozia A W Morawski B Grzmil M Janusand K Kałucki ldquoThe preparation of TiO
2-nitrogen doped by
calcination of TiO2sdot xH2O under ammonia atmosphere for
visible light photocatalysisrdquo Solar Energy Materials and SolarCells vol 88 no 3 pp 269ndash280 2005
[9] F Peng L Cai L Huang H Yu and H Wang ldquoPreparationof nitrogen-doped titanium dioxide with visible-light photocat-alytic activity using a facile hydrothermal methodrdquo Journal ofPhysics and Chemistry of Solids vol 69 no 7 pp 1657ndash16642008
[10] H Yu X Zheng Z Yin F Tag B Fang and K HouldquoPreparation of nitrogen-doped TiO
2nanoparticle catalyst and
its catalytic activity under visible lightrdquo Chinese Journal ofChemical Engineering vol 15 no 6 pp 802ndash807 2007
[11] Z Wang W Cai X Hong X Zhao F Xu and C CaildquoPhotocatalytic degradation of phenol in aqueous nitrogen-doped TiO
2suspensions with various light sourcesrdquo Applied
Catalysis B vol 57 no 3 pp 223ndash231 2005[12] A Trenczek-Zajac K Kowalski K Zakrzewska and M
Radecka ldquoNitrogen-doped titanium dioxidemdashcharacterizationof structural and optical propertiesrdquoMaterials ResearchBulletinvol 44 no 7 pp 1547ndash1552 2009
[13] J S Jang H G Kim S M Ji et al ldquoFormation of crystallineTiO2minus119909
N119909and its photocatalytic activityrdquo Journal of Solid State
Chemistry vol 179 no 4 pp 1067ndash1075 2006[14] H L Qin G B Gu and S Liu ldquoPreparation of nitrogen-doped
titania using sol-gel technique and its photocatalytic activityrdquo
Materials Chemistry and Physics vol 112 no 2 pp 346ndash3522008
[15] J Xu Y Ao D Fu andC Yuan J ldquoLow-temperature preparationof anatase titania-coated magnetiterdquo Journal of Physics andChemistry of Solids vol 69 pp 1980ndash1984 2008
[16] DWuM LongW Cai C Chen and YWu ldquoLow temperaturehydrothermal synthesis of N-doped TiO
2photocatalyst with
high visible-light activityrdquo Journal of Alloys andCompounds vol502 no 2 pp 289ndash294 2010
[17] K M Parida and B Naik ldquoSynthesis of mesoporous TiO2minus119909
N119909
spheres by template free homogeneous co-precipitationmethodand their photo-catalytic activity under visible light illumina-tionrdquo Journal of Colloid and Interface Science vol 333 no 1 pp269ndash276 2009
[18] N R Neti R Misra P K Bera R Dhodapkar S Bakardjievaand Z Bastl ldquoSynthesis of c-doped TiO
2nanoparticles by no-
vel sol-gel polycondensation of resorcinol with formaldehydefor visible-light photocatalysisrdquo Synthesis and Reactivity inInorganic Metal-Organic and Nano-Metal Chemistry vol 40no 5 pp 328ndash332 2010
[19] K Bubacz J Choina D Dolat E Borowiak-Palen D Mos-zynski and A W Morawski ldquoStudies on nitrogen modifiedTiO2photocatalyst prepared in different conditionsrdquoMaterials
Research Bulletin vol 45 no 9 pp 1085ndash1091 2010[20] Z Zhang X Wang J Long Q Gu Z Ding and X Fu
ldquoNitrogen-doped titanium dioxide visible light photocatalystspectroscopic identification of photoactive centersrdquo Journal ofCatalysis vol 276 pp 201ndash214 2010
[21] X Z Bu G K Zhang Y Y Gao and Y Q Yang ldquoPrepara-tion and photocatalytic properties of visible light responsiveN-doped TiO
2rectorite compositesrdquo Microporous and Meso-
porous Materials vol 136 no 1ndash3 pp 132ndash137 2010[22] C Liu X Tang C Mo and Z Qiang ldquoCharacterization and
activity of visible-light-driven TiO2photocatalyst codopedwith
nitrogen and ceriumrdquo Journal of Solid State Chemistry vol 181no 4 pp 913ndash919 2008
[23] R Kun S Tarjan AOszko et al ldquoPreparation and characteriza-tion of mesoporous N-doped and sulfuric acid treated anataseTiO2catalysts and their photocatalytic activity under UV and
Vis illuminationrdquo Journal of Solid State Chemistry vol 182 pp3076ndash3084 2009
[24] Z Pap L Baia K Mogyorosi A Dombi A Oszko and VDanciu ldquoCorrelating the visible light photoactivity of N-dopedTiO2with brookite particle size and bridged-nitro surface
speciesrdquo Catalysis Communications vol 17 pp 1ndash7 2012[25] X Z Bu G K Zhang and CH Zhang ldquoEffect of nitrogen dop-
ing on anatase-rutile phase transformation of TiO2rdquo Applied
Surface Science vol 258 pp 7997ndash8001 2012[26] Y P Peng E Yassitepe Y T Yeh I Ruzybayev S I Shah and C
P Huang ldquoPhotoelectrochemical degradation of azo dye overpulsed laser deposited nitrogen-doped TiO
2thin filmrdquo Applied
Catalysis B vol 125 pp 465ndash472 2012[27] H Jie H B Lee K H Chae et al ldquoNitrogen-doped
TiO2nanopowders prepared by chemical vapor synthesis
band structure and photocatalytic activity under visible lightrdquoResearch on Chemical Intermediates vol 38 no 6 pp 1171ndash11802012
[28] S U M Khan M Al-Shahry and W B Ingler ldquoEfficientphotochemical water splitting by a chemically modified n-TiO2rdquo Science vol 297 no 5590 pp 2243ndash2245 2002
International Journal of Photoenergy 13
[29] X X Wang S Meng X L Zhang H T Wang W Zhong andQ G Du ldquoMulti-type carbon doping of TiO
2photocatalystrdquo
Chemical Physics Letters vol 444 pp 292ndash296 2007[30] N R Khalid E Ahmed Z L Hong Y W Zhang and
M Ahmad ldquoNitrogen doped TiO2nanoparticles decorated
on graphene sheets for photocatalysis applicationsrdquo CurrentApplied Physics vol 12 no 6 pp 1485ndash1492 2012
[31] Q J Xiang J G Yu and M Jaroniec ldquoNitrogen and sulfurco-doped TiO
2nanosheets with exposed 001 facets synthesis
characterization and visible-light photocatalytic activityrdquo Phys-ical Chemistry Chemical Physics vol 13 no 11 pp 4853ndash48612011
[32] J Wang D N Tafen J P Lewis et al ldquoOrigin of photocatalyticactivity of nitrogen-doped TiO
2nanobeltsrdquo Journal of the
American Chemical Society vol 131 pp 12290ndash12297 2009[33] Q Xiang J YuWWang andM Jaroniec ldquoNitrogen self-doped
nanosized TiO2sheets with exposed 001 facets for enhanced
visible-light photocatalytic activityrdquoChemical Communicationsvol 47 no 24 pp 6906ndash6908 2011
[34] Y C Tang X H Huang H Q Yu and L H Tang ldquoNitrogen-doped TiO
2photocatalyst prepared by mechanochemical
method doping mechanisms and visible photoactivity of pol-lutant degradationrdquo International Journal of Photoenergy vol2012 Article ID 960726 10 pages 2012
[35] D E Gu Y Lu B C Yang and Y D Hu ldquoFacile preparationof micro-mesoporous carbon-doped TiO
2photocatalysts with
anatase crystalline walls under template-free conditionrdquo Chem-ical Communications no 21 pp 2453ndash2455 2008
[36] W Ren Z Ai F Jia L Zhang X Fan and Z Zou ldquoLow tem-perature preparation and visible light photocatalytic activity ofmesoporous carbon-doped crystalline TiO
2rdquo Applied Catalysis
B vol 69 no 3-4 pp 138ndash144 2007[37] EM Rockafellow X Fang B G Trewyn K Schmidt-Rohr and
W S Jenks ldquoSolid-state 13C NMR characterization of carbon-modified TiO
2rdquo Chemistry of Materials vol 21 no 7 pp 1187ndash
1197 2009[38] Y Zhang P Xiao X Zhou D Liu B B Garcia and G Cao
ldquoCarbon monoxide annealed TiO2nanotube array electrodes
for efficient biosensor applicationsrdquo Journal of Materials Chem-istry vol 19 no 7 pp 948ndash953 2009
[39] J Yu L Zhang B Cheng andY Su ldquoHydrothermal preparationand photocatalytic activity of hierarchically sponge-like macro-mesoporous Titaniardquo Journal of Physical Chemistry C vol 111no 28 pp 10582ndash10589 2007
[40] J Zhao and X Yang ldquoPhotocatalytic oxidation for indoor airpurification a literature reviewrdquo Building and Environment vol38 no 5 pp 645ndash654 2003
[41] C Di Valentin G Pacchioni and A Selloni ldquoOrigin of thedifferent photoactivity of N-doped anatase and rutile TiO
2rdquo
Physical ReviewB vol 70 no 8 Article ID 085116 4 pages 2004[42] S Livraghi M C Paganini E Giamello A Selloni C
Di Valentin and G Pacchioni ldquoOrigin of photoactivity ofnitrogen-doped titanium dioxide under visible lightrdquo Journal ofthe American Chemical Society vol 128 no 49 pp 15666ndash156712006
[43] X Chen and C Burda ldquoThe electronic origin of the visible-lightabsorption properties of C- N- and S-doped TiO
2nanomateri-
alsrdquo Journal of the American Chemical Society vol 130 no 15pp 5018ndash5019 2008
[44] C Di Valentin G Pacchioni and A Selloni ldquoTheory of carbondoping of titanium dioxiderdquo Chemistry of Materials vol 17 no26 pp 6656ndash6665 2005
[45] HWang and J P Lewis ldquoEffects of dopant states on photoactiv-ity in carbon-dopedTiO
2rdquo Journal of Physics CondensedMatter
vol 17 no 21 pp L209ndashL213 2005[46] H Li D Wang H Fan P Wang T Jiang and T Xie ldquoSynthesis
of highly efficient C-doped TiO2photocatalyst and its photo-
generated charge-transfer propertiesrdquo Journal of Colloid andInterface Science vol 354 no 1 pp 175ndash180 2011
[47] ZWu FDongWZhao and SGuo ldquoVisible light induced elec-tron transfer process over nitrogen doped TiO
2nanocrystals
prepared by oxidation of titaniumnitriderdquo Journal of HazardousMaterials vol 157 no 1 pp 57ndash63 2008
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
International Journal of Photoenergy 11
32 eVCO2 + H2O
IntermediatesH2O
OH∙ C2H4
eminuseminusTiIII OH
TiIV OH
TiIV OH
O2
∙O2minus
∙HOO H2O2
TiIV OH+∙
CB
VBh+ NS
OV
Figure 9 Schematic diagram for the process in the photooxidation of ethylene and electron transfer process over N-TiO2under visible light
illumination
involving electrons and (b) very stable surface peroxidegroups can be formed at the anatase during photo-oxidationreaction but not on the rutile surface [40] For the samplecalcined at 800∘C the removal efficiency decreased rapidlywhich can be due to its fewer amounts of anatase andsmall 119878BET The result indicates that higher specific surfacearea smaller crystallite size and good anatase crystallizationwill promote the photocatalytic activity in visible light Theresults indicate the N-TiO
2catalyst prepared with AT ratio
20 and calcinated at 400∘C shows the best photocatalyticability
37 The Formation Mechanism of N-Doped TiO2 For the
pure TiO2 the energy of the visible light is not sufficient
to excite electrons from the valence band (VB) as theintrinsic band gap of pure TiO
2 Based on the results of UV-
vis DRS XRD and XPS the nitrogen atoms were weavedinto the crystal structure of TiO
2with structure as TindashOndash
N N-TiO2was active in the visible light irradiation for
the degradation of ethylene The following explanation forthe photocatalytic activity of N-TiO
2in the visible light
spectra can be consideredThe nitrogen existing at interstitialpositions of TiO
2lattice induces localized occupied states and
forms midband gap leading to the red shift of absorptionedge and photocatalytic activity under visible light irradiation[41] The electron (eminus) can be excited from the N-impuritylevel to the conduction band (CB) The exited electrons aretrapped by O
2adsorbed on the catalyst surface producing
O2
minus∙ superoxide anion radicals After a series of reactions(1)ndash(12) ethylene molecules are finally mineralized into CO
2
DFT calcinations and experimental results indicate that N-doping favored the formation of O vacancy (subband levelO119907) which was below the bottom of the conduction band
[42ndash47] Therefore the electrons (eminus) are excited from theN-impurity level bond to the subband level (O
119907) and then
recombine with the hole (h+) as proved in Figure 9 Theholes and electrons react with OHminus and O
2molecules on the
catalyst surface to form ∙OH radicals and O2
minus∙ superoxideanion radicals respectivelyThe protonation yields theHOO∙radicals which after trapping electrons combine to produceH2O2 The O
2
minus∙ radicals then interact with H2O adsorbed to
produce more ∙OH radicals These ∙OH radicals then reactwith gaseous ethylene and mineralize it
TiO2
h120592997888997888997888997888997888rarr h+ + eminus (1)
SndashH2O + h+ 997888rarr SndashOH∙ +H+ (2)
SndashOHminus + h+ larrrarr SndashOH∙ (3)
S1015840ndashO2+ eminus 997888rarr S1015840ndashO
2
minus∙ (4)
SndashOH + S1015840ndashO2
minus∙997888rarr SndashHO
2
∙+ S1015840ndashOminus∙ (5)
S1015840ndashO2997888rarr 2S1015840ndashO (6)
S1015840ndashO + eminus 997888rarr S1015840ndashOminus∙ (7)
SndashH2O + S1015840ndashOminus∙ 997888rarr SndashOH∙ + SndashOHminus (8)
SndashHO2
∙+ SndashHO
2
∙997888rarr SndashH
2O2+O2
(9)
SndashH2O2997888rarr 2SndashOH∙ (10)
SndashC2H4+ SndashOH∙ larrrarr SndashC
2H4OH (11)
SndashC2H4OH + S1015840ndashO
2997888rarr intermediates 997888rarr CO
2+H2O(12)
4 Conclusions
The observed changes in the UV-vis DRS XRD and XPSspectra are providing consistent structural information forTindashOndashN formation that is the nitrogen can be incorporatedinto the interstitial positions of TiO
2lattice which leads to
the enhanced photocatalytic activity in N-TiO2samples It
is concluded that the photocatalytic oxidation reactivity ofN-TiO
2under visible light illumination is mainly due to the
presence of localized occupied states caused by interstitialnitrogen and the electronhole pairs generated under visiblelight irradiation It has been found that N dopant retardedthe anatase to rutile phase transformation by forming TindashOndashN incorporated into the interstitial position of TiO
2lattice
Moreover the transformation temperatures of anatase-to-rutile progressively slightly increase when N dopant contentis increased The photocatalyst N-TiO
2prepared with AT
ratio 20 and calcinated at 400∘C shows the highest photo-catalytic activity in the oxidation of ethylene This N-TiO
2
provides an effective visible-light-responsive photocatalystfor future industrial applications in pollution control
12 International Journal of Photoenergy
Acknowledgment
This research was financially supported by the NationalScience Council of Taiwan ROC under Grant nos NSC-100-2221-E-005-007 and NSC-100-2120-M-005-002
References
[1] T Horikawa M Katoh and T Tomida ldquoPreparation and char-acterization of nitrogen-doped mesoporous titania with highspecific surface areardquo Microporous and Mesoporous Materialsvol 110 no 2-3 pp 397ndash404 2008
[2] K Yang Y Dai and B Huang ldquoStudy of the nitrogen concen-tration influence onN-dopedTiO
2anatase fromfirst-principles
calculationsrdquo Journal of Physical Chemistry C vol 111 no 32 pp12086ndash12090 2007
[3] K Pomoni A Vomvas and C Trapalis ldquoDark conductivity andtransient photoconductivity of nanocrystalline undoped andN-doped TiO
2sol-gel thin filmsrdquoThin Solid Films vol 516 no 6
pp 1271ndash1278 2008[4] S Sato ldquoPhotocatalytic activity of NO
119909-doped TiO
2in the
visible light regionrdquo Chemical Physics Letters vol 123 no 1-2pp 126ndash128 1986
[5] R Asahi T Morikawa T Ohwaki K Aoki and Y TagaldquoVisible-light photocatalysis in nitrogen-doped titaniumoxidesrdquo Science vol 293 no 5528 pp 269ndash271 2001
[6] J Ananpattarachai P Kajitvichyanukul and S Seraphin ldquoVisi-ble light absorption ability and photocatalytic oxidation activityof various interstitial N-doped TiO
2prepared from different
nitrogen dopantsrdquo Journal of Hazardous Materials vol 168 no1 pp 253ndash261 2009
[7] Y T Lin C HWeng and TW Tzeng ldquoPhotocatalysis and cat-alytic properties of nano-sized N-TiO
2catalyst synthesized by
Sol-gel methodsrdquo Journal of Advanced Oxidation Technologiesvol 13 no 3 pp 297ndash304 2010
[8] B Kosowska S Mozia A W Morawski B Grzmil M Janusand K Kałucki ldquoThe preparation of TiO
2-nitrogen doped by
calcination of TiO2sdot xH2O under ammonia atmosphere for
visible light photocatalysisrdquo Solar Energy Materials and SolarCells vol 88 no 3 pp 269ndash280 2005
[9] F Peng L Cai L Huang H Yu and H Wang ldquoPreparationof nitrogen-doped titanium dioxide with visible-light photocat-alytic activity using a facile hydrothermal methodrdquo Journal ofPhysics and Chemistry of Solids vol 69 no 7 pp 1657ndash16642008
[10] H Yu X Zheng Z Yin F Tag B Fang and K HouldquoPreparation of nitrogen-doped TiO
2nanoparticle catalyst and
its catalytic activity under visible lightrdquo Chinese Journal ofChemical Engineering vol 15 no 6 pp 802ndash807 2007
[11] Z Wang W Cai X Hong X Zhao F Xu and C CaildquoPhotocatalytic degradation of phenol in aqueous nitrogen-doped TiO
2suspensions with various light sourcesrdquo Applied
Catalysis B vol 57 no 3 pp 223ndash231 2005[12] A Trenczek-Zajac K Kowalski K Zakrzewska and M
Radecka ldquoNitrogen-doped titanium dioxidemdashcharacterizationof structural and optical propertiesrdquoMaterials ResearchBulletinvol 44 no 7 pp 1547ndash1552 2009
[13] J S Jang H G Kim S M Ji et al ldquoFormation of crystallineTiO2minus119909
N119909and its photocatalytic activityrdquo Journal of Solid State
Chemistry vol 179 no 4 pp 1067ndash1075 2006[14] H L Qin G B Gu and S Liu ldquoPreparation of nitrogen-doped
titania using sol-gel technique and its photocatalytic activityrdquo
Materials Chemistry and Physics vol 112 no 2 pp 346ndash3522008
[15] J Xu Y Ao D Fu andC Yuan J ldquoLow-temperature preparationof anatase titania-coated magnetiterdquo Journal of Physics andChemistry of Solids vol 69 pp 1980ndash1984 2008
[16] DWuM LongW Cai C Chen and YWu ldquoLow temperaturehydrothermal synthesis of N-doped TiO
2photocatalyst with
high visible-light activityrdquo Journal of Alloys andCompounds vol502 no 2 pp 289ndash294 2010
[17] K M Parida and B Naik ldquoSynthesis of mesoporous TiO2minus119909
N119909
spheres by template free homogeneous co-precipitationmethodand their photo-catalytic activity under visible light illumina-tionrdquo Journal of Colloid and Interface Science vol 333 no 1 pp269ndash276 2009
[18] N R Neti R Misra P K Bera R Dhodapkar S Bakardjievaand Z Bastl ldquoSynthesis of c-doped TiO
2nanoparticles by no-
vel sol-gel polycondensation of resorcinol with formaldehydefor visible-light photocatalysisrdquo Synthesis and Reactivity inInorganic Metal-Organic and Nano-Metal Chemistry vol 40no 5 pp 328ndash332 2010
[19] K Bubacz J Choina D Dolat E Borowiak-Palen D Mos-zynski and A W Morawski ldquoStudies on nitrogen modifiedTiO2photocatalyst prepared in different conditionsrdquoMaterials
Research Bulletin vol 45 no 9 pp 1085ndash1091 2010[20] Z Zhang X Wang J Long Q Gu Z Ding and X Fu
ldquoNitrogen-doped titanium dioxide visible light photocatalystspectroscopic identification of photoactive centersrdquo Journal ofCatalysis vol 276 pp 201ndash214 2010
[21] X Z Bu G K Zhang Y Y Gao and Y Q Yang ldquoPrepara-tion and photocatalytic properties of visible light responsiveN-doped TiO
2rectorite compositesrdquo Microporous and Meso-
porous Materials vol 136 no 1ndash3 pp 132ndash137 2010[22] C Liu X Tang C Mo and Z Qiang ldquoCharacterization and
activity of visible-light-driven TiO2photocatalyst codopedwith
nitrogen and ceriumrdquo Journal of Solid State Chemistry vol 181no 4 pp 913ndash919 2008
[23] R Kun S Tarjan AOszko et al ldquoPreparation and characteriza-tion of mesoporous N-doped and sulfuric acid treated anataseTiO2catalysts and their photocatalytic activity under UV and
Vis illuminationrdquo Journal of Solid State Chemistry vol 182 pp3076ndash3084 2009
[24] Z Pap L Baia K Mogyorosi A Dombi A Oszko and VDanciu ldquoCorrelating the visible light photoactivity of N-dopedTiO2with brookite particle size and bridged-nitro surface
speciesrdquo Catalysis Communications vol 17 pp 1ndash7 2012[25] X Z Bu G K Zhang and CH Zhang ldquoEffect of nitrogen dop-
ing on anatase-rutile phase transformation of TiO2rdquo Applied
Surface Science vol 258 pp 7997ndash8001 2012[26] Y P Peng E Yassitepe Y T Yeh I Ruzybayev S I Shah and C
P Huang ldquoPhotoelectrochemical degradation of azo dye overpulsed laser deposited nitrogen-doped TiO
2thin filmrdquo Applied
Catalysis B vol 125 pp 465ndash472 2012[27] H Jie H B Lee K H Chae et al ldquoNitrogen-doped
TiO2nanopowders prepared by chemical vapor synthesis
band structure and photocatalytic activity under visible lightrdquoResearch on Chemical Intermediates vol 38 no 6 pp 1171ndash11802012
[28] S U M Khan M Al-Shahry and W B Ingler ldquoEfficientphotochemical water splitting by a chemically modified n-TiO2rdquo Science vol 297 no 5590 pp 2243ndash2245 2002
International Journal of Photoenergy 13
[29] X X Wang S Meng X L Zhang H T Wang W Zhong andQ G Du ldquoMulti-type carbon doping of TiO
2photocatalystrdquo
Chemical Physics Letters vol 444 pp 292ndash296 2007[30] N R Khalid E Ahmed Z L Hong Y W Zhang and
M Ahmad ldquoNitrogen doped TiO2nanoparticles decorated
on graphene sheets for photocatalysis applicationsrdquo CurrentApplied Physics vol 12 no 6 pp 1485ndash1492 2012
[31] Q J Xiang J G Yu and M Jaroniec ldquoNitrogen and sulfurco-doped TiO
2nanosheets with exposed 001 facets synthesis
characterization and visible-light photocatalytic activityrdquo Phys-ical Chemistry Chemical Physics vol 13 no 11 pp 4853ndash48612011
[32] J Wang D N Tafen J P Lewis et al ldquoOrigin of photocatalyticactivity of nitrogen-doped TiO
2nanobeltsrdquo Journal of the
American Chemical Society vol 131 pp 12290ndash12297 2009[33] Q Xiang J YuWWang andM Jaroniec ldquoNitrogen self-doped
nanosized TiO2sheets with exposed 001 facets for enhanced
visible-light photocatalytic activityrdquoChemical Communicationsvol 47 no 24 pp 6906ndash6908 2011
[34] Y C Tang X H Huang H Q Yu and L H Tang ldquoNitrogen-doped TiO
2photocatalyst prepared by mechanochemical
method doping mechanisms and visible photoactivity of pol-lutant degradationrdquo International Journal of Photoenergy vol2012 Article ID 960726 10 pages 2012
[35] D E Gu Y Lu B C Yang and Y D Hu ldquoFacile preparationof micro-mesoporous carbon-doped TiO
2photocatalysts with
anatase crystalline walls under template-free conditionrdquo Chem-ical Communications no 21 pp 2453ndash2455 2008
[36] W Ren Z Ai F Jia L Zhang X Fan and Z Zou ldquoLow tem-perature preparation and visible light photocatalytic activity ofmesoporous carbon-doped crystalline TiO
2rdquo Applied Catalysis
B vol 69 no 3-4 pp 138ndash144 2007[37] EM Rockafellow X Fang B G Trewyn K Schmidt-Rohr and
W S Jenks ldquoSolid-state 13C NMR characterization of carbon-modified TiO
2rdquo Chemistry of Materials vol 21 no 7 pp 1187ndash
1197 2009[38] Y Zhang P Xiao X Zhou D Liu B B Garcia and G Cao
ldquoCarbon monoxide annealed TiO2nanotube array electrodes
for efficient biosensor applicationsrdquo Journal of Materials Chem-istry vol 19 no 7 pp 948ndash953 2009
[39] J Yu L Zhang B Cheng andY Su ldquoHydrothermal preparationand photocatalytic activity of hierarchically sponge-like macro-mesoporous Titaniardquo Journal of Physical Chemistry C vol 111no 28 pp 10582ndash10589 2007
[40] J Zhao and X Yang ldquoPhotocatalytic oxidation for indoor airpurification a literature reviewrdquo Building and Environment vol38 no 5 pp 645ndash654 2003
[41] C Di Valentin G Pacchioni and A Selloni ldquoOrigin of thedifferent photoactivity of N-doped anatase and rutile TiO
2rdquo
Physical ReviewB vol 70 no 8 Article ID 085116 4 pages 2004[42] S Livraghi M C Paganini E Giamello A Selloni C
Di Valentin and G Pacchioni ldquoOrigin of photoactivity ofnitrogen-doped titanium dioxide under visible lightrdquo Journal ofthe American Chemical Society vol 128 no 49 pp 15666ndash156712006
[43] X Chen and C Burda ldquoThe electronic origin of the visible-lightabsorption properties of C- N- and S-doped TiO
2nanomateri-
alsrdquo Journal of the American Chemical Society vol 130 no 15pp 5018ndash5019 2008
[44] C Di Valentin G Pacchioni and A Selloni ldquoTheory of carbondoping of titanium dioxiderdquo Chemistry of Materials vol 17 no26 pp 6656ndash6665 2005
[45] HWang and J P Lewis ldquoEffects of dopant states on photoactiv-ity in carbon-dopedTiO
2rdquo Journal of Physics CondensedMatter
vol 17 no 21 pp L209ndashL213 2005[46] H Li D Wang H Fan P Wang T Jiang and T Xie ldquoSynthesis
of highly efficient C-doped TiO2photocatalyst and its photo-
generated charge-transfer propertiesrdquo Journal of Colloid andInterface Science vol 354 no 1 pp 175ndash180 2011
[47] ZWu FDongWZhao and SGuo ldquoVisible light induced elec-tron transfer process over nitrogen doped TiO
2nanocrystals
prepared by oxidation of titaniumnitriderdquo Journal of HazardousMaterials vol 157 no 1 pp 57ndash63 2008
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
12 International Journal of Photoenergy
Acknowledgment
This research was financially supported by the NationalScience Council of Taiwan ROC under Grant nos NSC-100-2221-E-005-007 and NSC-100-2120-M-005-002
References
[1] T Horikawa M Katoh and T Tomida ldquoPreparation and char-acterization of nitrogen-doped mesoporous titania with highspecific surface areardquo Microporous and Mesoporous Materialsvol 110 no 2-3 pp 397ndash404 2008
[2] K Yang Y Dai and B Huang ldquoStudy of the nitrogen concen-tration influence onN-dopedTiO
2anatase fromfirst-principles
calculationsrdquo Journal of Physical Chemistry C vol 111 no 32 pp12086ndash12090 2007
[3] K Pomoni A Vomvas and C Trapalis ldquoDark conductivity andtransient photoconductivity of nanocrystalline undoped andN-doped TiO
2sol-gel thin filmsrdquoThin Solid Films vol 516 no 6
pp 1271ndash1278 2008[4] S Sato ldquoPhotocatalytic activity of NO
119909-doped TiO
2in the
visible light regionrdquo Chemical Physics Letters vol 123 no 1-2pp 126ndash128 1986
[5] R Asahi T Morikawa T Ohwaki K Aoki and Y TagaldquoVisible-light photocatalysis in nitrogen-doped titaniumoxidesrdquo Science vol 293 no 5528 pp 269ndash271 2001
[6] J Ananpattarachai P Kajitvichyanukul and S Seraphin ldquoVisi-ble light absorption ability and photocatalytic oxidation activityof various interstitial N-doped TiO
2prepared from different
nitrogen dopantsrdquo Journal of Hazardous Materials vol 168 no1 pp 253ndash261 2009
[7] Y T Lin C HWeng and TW Tzeng ldquoPhotocatalysis and cat-alytic properties of nano-sized N-TiO
2catalyst synthesized by
Sol-gel methodsrdquo Journal of Advanced Oxidation Technologiesvol 13 no 3 pp 297ndash304 2010
[8] B Kosowska S Mozia A W Morawski B Grzmil M Janusand K Kałucki ldquoThe preparation of TiO
2-nitrogen doped by
calcination of TiO2sdot xH2O under ammonia atmosphere for
visible light photocatalysisrdquo Solar Energy Materials and SolarCells vol 88 no 3 pp 269ndash280 2005
[9] F Peng L Cai L Huang H Yu and H Wang ldquoPreparationof nitrogen-doped titanium dioxide with visible-light photocat-alytic activity using a facile hydrothermal methodrdquo Journal ofPhysics and Chemistry of Solids vol 69 no 7 pp 1657ndash16642008
[10] H Yu X Zheng Z Yin F Tag B Fang and K HouldquoPreparation of nitrogen-doped TiO
2nanoparticle catalyst and
its catalytic activity under visible lightrdquo Chinese Journal ofChemical Engineering vol 15 no 6 pp 802ndash807 2007
[11] Z Wang W Cai X Hong X Zhao F Xu and C CaildquoPhotocatalytic degradation of phenol in aqueous nitrogen-doped TiO
2suspensions with various light sourcesrdquo Applied
Catalysis B vol 57 no 3 pp 223ndash231 2005[12] A Trenczek-Zajac K Kowalski K Zakrzewska and M
Radecka ldquoNitrogen-doped titanium dioxidemdashcharacterizationof structural and optical propertiesrdquoMaterials ResearchBulletinvol 44 no 7 pp 1547ndash1552 2009
[13] J S Jang H G Kim S M Ji et al ldquoFormation of crystallineTiO2minus119909
N119909and its photocatalytic activityrdquo Journal of Solid State
Chemistry vol 179 no 4 pp 1067ndash1075 2006[14] H L Qin G B Gu and S Liu ldquoPreparation of nitrogen-doped
titania using sol-gel technique and its photocatalytic activityrdquo
Materials Chemistry and Physics vol 112 no 2 pp 346ndash3522008
[15] J Xu Y Ao D Fu andC Yuan J ldquoLow-temperature preparationof anatase titania-coated magnetiterdquo Journal of Physics andChemistry of Solids vol 69 pp 1980ndash1984 2008
[16] DWuM LongW Cai C Chen and YWu ldquoLow temperaturehydrothermal synthesis of N-doped TiO
2photocatalyst with
high visible-light activityrdquo Journal of Alloys andCompounds vol502 no 2 pp 289ndash294 2010
[17] K M Parida and B Naik ldquoSynthesis of mesoporous TiO2minus119909
N119909
spheres by template free homogeneous co-precipitationmethodand their photo-catalytic activity under visible light illumina-tionrdquo Journal of Colloid and Interface Science vol 333 no 1 pp269ndash276 2009
[18] N R Neti R Misra P K Bera R Dhodapkar S Bakardjievaand Z Bastl ldquoSynthesis of c-doped TiO
2nanoparticles by no-
vel sol-gel polycondensation of resorcinol with formaldehydefor visible-light photocatalysisrdquo Synthesis and Reactivity inInorganic Metal-Organic and Nano-Metal Chemistry vol 40no 5 pp 328ndash332 2010
[19] K Bubacz J Choina D Dolat E Borowiak-Palen D Mos-zynski and A W Morawski ldquoStudies on nitrogen modifiedTiO2photocatalyst prepared in different conditionsrdquoMaterials
Research Bulletin vol 45 no 9 pp 1085ndash1091 2010[20] Z Zhang X Wang J Long Q Gu Z Ding and X Fu
ldquoNitrogen-doped titanium dioxide visible light photocatalystspectroscopic identification of photoactive centersrdquo Journal ofCatalysis vol 276 pp 201ndash214 2010
[21] X Z Bu G K Zhang Y Y Gao and Y Q Yang ldquoPrepara-tion and photocatalytic properties of visible light responsiveN-doped TiO
2rectorite compositesrdquo Microporous and Meso-
porous Materials vol 136 no 1ndash3 pp 132ndash137 2010[22] C Liu X Tang C Mo and Z Qiang ldquoCharacterization and
activity of visible-light-driven TiO2photocatalyst codopedwith
nitrogen and ceriumrdquo Journal of Solid State Chemistry vol 181no 4 pp 913ndash919 2008
[23] R Kun S Tarjan AOszko et al ldquoPreparation and characteriza-tion of mesoporous N-doped and sulfuric acid treated anataseTiO2catalysts and their photocatalytic activity under UV and
Vis illuminationrdquo Journal of Solid State Chemistry vol 182 pp3076ndash3084 2009
[24] Z Pap L Baia K Mogyorosi A Dombi A Oszko and VDanciu ldquoCorrelating the visible light photoactivity of N-dopedTiO2with brookite particle size and bridged-nitro surface
speciesrdquo Catalysis Communications vol 17 pp 1ndash7 2012[25] X Z Bu G K Zhang and CH Zhang ldquoEffect of nitrogen dop-
ing on anatase-rutile phase transformation of TiO2rdquo Applied
Surface Science vol 258 pp 7997ndash8001 2012[26] Y P Peng E Yassitepe Y T Yeh I Ruzybayev S I Shah and C
P Huang ldquoPhotoelectrochemical degradation of azo dye overpulsed laser deposited nitrogen-doped TiO
2thin filmrdquo Applied
Catalysis B vol 125 pp 465ndash472 2012[27] H Jie H B Lee K H Chae et al ldquoNitrogen-doped
TiO2nanopowders prepared by chemical vapor synthesis
band structure and photocatalytic activity under visible lightrdquoResearch on Chemical Intermediates vol 38 no 6 pp 1171ndash11802012
[28] S U M Khan M Al-Shahry and W B Ingler ldquoEfficientphotochemical water splitting by a chemically modified n-TiO2rdquo Science vol 297 no 5590 pp 2243ndash2245 2002
International Journal of Photoenergy 13
[29] X X Wang S Meng X L Zhang H T Wang W Zhong andQ G Du ldquoMulti-type carbon doping of TiO
2photocatalystrdquo
Chemical Physics Letters vol 444 pp 292ndash296 2007[30] N R Khalid E Ahmed Z L Hong Y W Zhang and
M Ahmad ldquoNitrogen doped TiO2nanoparticles decorated
on graphene sheets for photocatalysis applicationsrdquo CurrentApplied Physics vol 12 no 6 pp 1485ndash1492 2012
[31] Q J Xiang J G Yu and M Jaroniec ldquoNitrogen and sulfurco-doped TiO
2nanosheets with exposed 001 facets synthesis
characterization and visible-light photocatalytic activityrdquo Phys-ical Chemistry Chemical Physics vol 13 no 11 pp 4853ndash48612011
[32] J Wang D N Tafen J P Lewis et al ldquoOrigin of photocatalyticactivity of nitrogen-doped TiO
2nanobeltsrdquo Journal of the
American Chemical Society vol 131 pp 12290ndash12297 2009[33] Q Xiang J YuWWang andM Jaroniec ldquoNitrogen self-doped
nanosized TiO2sheets with exposed 001 facets for enhanced
visible-light photocatalytic activityrdquoChemical Communicationsvol 47 no 24 pp 6906ndash6908 2011
[34] Y C Tang X H Huang H Q Yu and L H Tang ldquoNitrogen-doped TiO
2photocatalyst prepared by mechanochemical
method doping mechanisms and visible photoactivity of pol-lutant degradationrdquo International Journal of Photoenergy vol2012 Article ID 960726 10 pages 2012
[35] D E Gu Y Lu B C Yang and Y D Hu ldquoFacile preparationof micro-mesoporous carbon-doped TiO
2photocatalysts with
anatase crystalline walls under template-free conditionrdquo Chem-ical Communications no 21 pp 2453ndash2455 2008
[36] W Ren Z Ai F Jia L Zhang X Fan and Z Zou ldquoLow tem-perature preparation and visible light photocatalytic activity ofmesoporous carbon-doped crystalline TiO
2rdquo Applied Catalysis
B vol 69 no 3-4 pp 138ndash144 2007[37] EM Rockafellow X Fang B G Trewyn K Schmidt-Rohr and
W S Jenks ldquoSolid-state 13C NMR characterization of carbon-modified TiO
2rdquo Chemistry of Materials vol 21 no 7 pp 1187ndash
1197 2009[38] Y Zhang P Xiao X Zhou D Liu B B Garcia and G Cao
ldquoCarbon monoxide annealed TiO2nanotube array electrodes
for efficient biosensor applicationsrdquo Journal of Materials Chem-istry vol 19 no 7 pp 948ndash953 2009
[39] J Yu L Zhang B Cheng andY Su ldquoHydrothermal preparationand photocatalytic activity of hierarchically sponge-like macro-mesoporous Titaniardquo Journal of Physical Chemistry C vol 111no 28 pp 10582ndash10589 2007
[40] J Zhao and X Yang ldquoPhotocatalytic oxidation for indoor airpurification a literature reviewrdquo Building and Environment vol38 no 5 pp 645ndash654 2003
[41] C Di Valentin G Pacchioni and A Selloni ldquoOrigin of thedifferent photoactivity of N-doped anatase and rutile TiO
2rdquo
Physical ReviewB vol 70 no 8 Article ID 085116 4 pages 2004[42] S Livraghi M C Paganini E Giamello A Selloni C
Di Valentin and G Pacchioni ldquoOrigin of photoactivity ofnitrogen-doped titanium dioxide under visible lightrdquo Journal ofthe American Chemical Society vol 128 no 49 pp 15666ndash156712006
[43] X Chen and C Burda ldquoThe electronic origin of the visible-lightabsorption properties of C- N- and S-doped TiO
2nanomateri-
alsrdquo Journal of the American Chemical Society vol 130 no 15pp 5018ndash5019 2008
[44] C Di Valentin G Pacchioni and A Selloni ldquoTheory of carbondoping of titanium dioxiderdquo Chemistry of Materials vol 17 no26 pp 6656ndash6665 2005
[45] HWang and J P Lewis ldquoEffects of dopant states on photoactiv-ity in carbon-dopedTiO
2rdquo Journal of Physics CondensedMatter
vol 17 no 21 pp L209ndashL213 2005[46] H Li D Wang H Fan P Wang T Jiang and T Xie ldquoSynthesis
of highly efficient C-doped TiO2photocatalyst and its photo-
generated charge-transfer propertiesrdquo Journal of Colloid andInterface Science vol 354 no 1 pp 175ndash180 2011
[47] ZWu FDongWZhao and SGuo ldquoVisible light induced elec-tron transfer process over nitrogen doped TiO
2nanocrystals
prepared by oxidation of titaniumnitriderdquo Journal of HazardousMaterials vol 157 no 1 pp 57ndash63 2008
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
International Journal of Photoenergy 13
[29] X X Wang S Meng X L Zhang H T Wang W Zhong andQ G Du ldquoMulti-type carbon doping of TiO
2photocatalystrdquo
Chemical Physics Letters vol 444 pp 292ndash296 2007[30] N R Khalid E Ahmed Z L Hong Y W Zhang and
M Ahmad ldquoNitrogen doped TiO2nanoparticles decorated
on graphene sheets for photocatalysis applicationsrdquo CurrentApplied Physics vol 12 no 6 pp 1485ndash1492 2012
[31] Q J Xiang J G Yu and M Jaroniec ldquoNitrogen and sulfurco-doped TiO
2nanosheets with exposed 001 facets synthesis
characterization and visible-light photocatalytic activityrdquo Phys-ical Chemistry Chemical Physics vol 13 no 11 pp 4853ndash48612011
[32] J Wang D N Tafen J P Lewis et al ldquoOrigin of photocatalyticactivity of nitrogen-doped TiO
2nanobeltsrdquo Journal of the
American Chemical Society vol 131 pp 12290ndash12297 2009[33] Q Xiang J YuWWang andM Jaroniec ldquoNitrogen self-doped
nanosized TiO2sheets with exposed 001 facets for enhanced
visible-light photocatalytic activityrdquoChemical Communicationsvol 47 no 24 pp 6906ndash6908 2011
[34] Y C Tang X H Huang H Q Yu and L H Tang ldquoNitrogen-doped TiO
2photocatalyst prepared by mechanochemical
method doping mechanisms and visible photoactivity of pol-lutant degradationrdquo International Journal of Photoenergy vol2012 Article ID 960726 10 pages 2012
[35] D E Gu Y Lu B C Yang and Y D Hu ldquoFacile preparationof micro-mesoporous carbon-doped TiO
2photocatalysts with
anatase crystalline walls under template-free conditionrdquo Chem-ical Communications no 21 pp 2453ndash2455 2008
[36] W Ren Z Ai F Jia L Zhang X Fan and Z Zou ldquoLow tem-perature preparation and visible light photocatalytic activity ofmesoporous carbon-doped crystalline TiO
2rdquo Applied Catalysis
B vol 69 no 3-4 pp 138ndash144 2007[37] EM Rockafellow X Fang B G Trewyn K Schmidt-Rohr and
W S Jenks ldquoSolid-state 13C NMR characterization of carbon-modified TiO
2rdquo Chemistry of Materials vol 21 no 7 pp 1187ndash
1197 2009[38] Y Zhang P Xiao X Zhou D Liu B B Garcia and G Cao
ldquoCarbon monoxide annealed TiO2nanotube array electrodes
for efficient biosensor applicationsrdquo Journal of Materials Chem-istry vol 19 no 7 pp 948ndash953 2009
[39] J Yu L Zhang B Cheng andY Su ldquoHydrothermal preparationand photocatalytic activity of hierarchically sponge-like macro-mesoporous Titaniardquo Journal of Physical Chemistry C vol 111no 28 pp 10582ndash10589 2007
[40] J Zhao and X Yang ldquoPhotocatalytic oxidation for indoor airpurification a literature reviewrdquo Building and Environment vol38 no 5 pp 645ndash654 2003
[41] C Di Valentin G Pacchioni and A Selloni ldquoOrigin of thedifferent photoactivity of N-doped anatase and rutile TiO
2rdquo
Physical ReviewB vol 70 no 8 Article ID 085116 4 pages 2004[42] S Livraghi M C Paganini E Giamello A Selloni C
Di Valentin and G Pacchioni ldquoOrigin of photoactivity ofnitrogen-doped titanium dioxide under visible lightrdquo Journal ofthe American Chemical Society vol 128 no 49 pp 15666ndash156712006
[43] X Chen and C Burda ldquoThe electronic origin of the visible-lightabsorption properties of C- N- and S-doped TiO
2nanomateri-
alsrdquo Journal of the American Chemical Society vol 130 no 15pp 5018ndash5019 2008
[44] C Di Valentin G Pacchioni and A Selloni ldquoTheory of carbondoping of titanium dioxiderdquo Chemistry of Materials vol 17 no26 pp 6656ndash6665 2005
[45] HWang and J P Lewis ldquoEffects of dopant states on photoactiv-ity in carbon-dopedTiO
2rdquo Journal of Physics CondensedMatter
vol 17 no 21 pp L209ndashL213 2005[46] H Li D Wang H Fan P Wang T Jiang and T Xie ldquoSynthesis
of highly efficient C-doped TiO2photocatalyst and its photo-
generated charge-transfer propertiesrdquo Journal of Colloid andInterface Science vol 354 no 1 pp 175ndash180 2011
[47] ZWu FDongWZhao and SGuo ldquoVisible light induced elec-tron transfer process over nitrogen doped TiO
2nanocrystals
prepared by oxidation of titaniumnitriderdquo Journal of HazardousMaterials vol 157 no 1 pp 57ndash63 2008
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of