Research ArticleSynthesis and Characterization of CeriumDoped Titanium Catalyst for the Degradation ofNitrobenzene Using Visible Light

Padmini Ellappan and Lima Rose Miranda

Department of Chemical Engineering A C Tech Anna University Chennai 600 025 India

Correspondence should be addressed to Lima Rose Miranda limamiranda2007gmailcom

Received 22 May 2013 Accepted 3 October 2013 Published 6 January 2014

Academic Editor Manickavachagam Muruganandham

Copyright copy 2014 P Ellappan and L R Miranda This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

Cerium doped catalyst was synthesized using Titanium isopropoxide as the Titanium source The metal doped nanoparticlessemiconductor catalyst was prepared by sol-sol methodwith the sol of CeriumThe synthesized catalyst samples were characterizedby powder X-ray diffraction BET surface area thermogravimetric analysis (TGA) scanning electron microscopy (SEM) andUV-vis diffuse reflectance measurements (DRS) and compared with undoped TiO

2catalyst The photocatalytic activity of the

sample was investigated for the decomposition of nitrobenzene (NB) using visible light as the artificial light source Cerium dopedcatalyst was found to have better degradation of nitrobenzene owing to its shift in the band gap from UV to visible region ascompared to undoped TiO

2catalyst The operational parameters were optimized with catalyst dosage of 01 g Lminus1 pH of 9 and

light intensity of 500W The degradation mechanism followed the Langmuir Hinshelwood kinetic model with the rate constantdepending nonlinearly on the operational parameters as given by the relationship 119870app (theoretical) = 229 lowast 10minus4lowast Intensity0584lowastConcentrationminus0230lowast Dosage0425lowast pH0336

1 Introduction

The mechanism of photocatalysis using a semiconductor isby charge carrier generation resulting in the formation ofholes charge carrier trapping to form hydroxyl radicals andrecombination of electrons and holes where heat is generated

Heterogeneous photocatalytic systems based onTiO2cat-

alysts show some limitations that reduce their impact in thedomain of environmental protection Important limitationsare low photonic yield and little efficiency under visible lightThese limitations have recently been the source of great devel-opment in the area of the production and characterization ofTiO2-based photocatalysts capable of being efficiently used

under visible irradiation or showing a higher photochemicalyield in the near UV region

Any semiconductor material could be activated using alight whose wavelength greatly depends on the band gap ofthe semiconductor catalyst Apart from the band gapthere have been other properties like surface area crystal

composition particle size distribution and porosity whichhave an influential effect on the degradation of the com-pound Band gap reduction could be done by dye sensiti-zation doping bimetallic semiconductor and surface modi-fication By reducing the band gap use of visible light couldbe employed as an alternative to UV light whichmay result inbetter economics Various nonmetal elements such as B [1] C[2] N [3] V [4] and S [5] have been successfully doped intoTiO2nanomaterials Surface area crystal composition and

particle size distribution can be varied by varying the prepa-rationmethods like preparation using solgel method whereinuniform crystal structure with better properties could beachieved Several researchers have modified TiO

2with

transition metals Deposition of noble metals Ag Au Pt andPd [6 7] on the surface of TiO

2enhances the photocatalytic

efficiency by acting as an electron trap promoting interfacialcharge transfer and therefore delaying recombination of theelectron-hole pair Another technique involves TiO

2doping

with transition metals such as Fe Cu Co Ni Cr V Mn

Hindawi Publishing CorporationInternational Journal of PhotoenergyVolume 2014 Article ID 756408 9 pageshttpdxdoiorg1011552014756408

2 International Journal of Photoenergy

Mo Nb W Ru Pt and Au [8 9] The incorporation oftransition metals in the titania crystal lattice may result inthe formation of new energy levels between valence band andconduction band inducing a shift of light absorption towardsthe visible light region Photocatalytic activity depends on thenature and the amount of doping agent Possible limitationsare photocorrosion and promoted charge recombination atmetal sites Choi et al [10] has made an extensive study bydoping with Fe3+ Mo5+ Ru3+ Os3+ Re5+ V4+ and Rh3+ andconcluded that there was an increase in the photoreactivityfor both oxidation and reduction of the organic compound

Cerium among the lanthanides has a band gap of sim3 eVHence it has strong absorption and shows better opticalproperties Ce (III) and Ce (IV) have the high oxygenstorage capacity which enhances the catalytic potential alsoits oxidation ability of Ce3+ toCe4+ states leads to high oxygenmobility resulting in better catalytic performance [11 12] Ithas also been demonstrated by many researchers that thereare many advantages because of Cerium doping [13] Chen etal [14] and Liu et al [15] have also established that there wasa shift towards visible region due to doping of titania withCerium

Nitrobenzene an aromatic compound used in the manu-facture of aniline has moderate to low water solubility Thisnitroaromatic compound has been listed as a carcinogen bythe National Institute of Environmental Health Sciences Themaximum permissible limit for Nitrobenzene in drinkingwater is 17 ppm as recommended by the US EPA Nitroben-zene has been widely used as solvent and in manufactureof dye intermediates and pesticides Due to its carcinogenicand mutagenic properties it has to be eliminated from thewater streams Prolonged exposure causes damage to lung byirritation anaemia and liver damage A number of workersillustrate the removal or degradation of this compound bydifferent biologicalmethods like bioaugmentation and oxida-tive reduction by bioremediationWorks has been carried outon the degradation of nitrobenzene using white root fungusand glow discharge plasma Owing to the disadvantages ofthese procedures due to noneconomical degradation timeand complicated equipment designs leading to increased costthere has been extensive research in identifying techniqueswhich would show better performance One such techniquefound to be effective over the years is the use of advancedoxidation process photocatalysis Authors like Tayade etal [6] Priya and Madras [7] and Bhatkhande et al [16]have worked on the degradation of Nitrobenzene usingsemiconductor catalysts and an artificial light source

The main objectives of the present research work are (i)synthesis and characterization of TiO

2doped with Cerium

photocatalysts (ii) photocatalytic degradation of Nitroben-zene pollutant in aqueous suspensions using the dopedcatalyst and undoped catalyst under visible light (iii) opti-mization of operational parameters and (iv) detailed kineticstudy using Langmuir Hinshelwood model

2 Experimental Procedures

21 Chemical Reagents and Apparatus All chemicals usedin this experiment were of analytical grade Titanium

isopropoxide Titanium dioxide Cerium oxide ethanol andglacial acetic acid are supplied by SRL chemicals MumbaiIndia In all the experiments double distilled water was used

22 Catalyst Characterization X-ray diffraction (XRD)(Siemens D5000) was performed on fresh synthesizedcatalyst The X-ray powder diffraction pattern of the powdersample was measured employing CuK120572 radiation The datawere collected over diffraction angle of 5∘ to 80∘ in 2120579 witha step scanning The accelerating voltage and the appliedcurrent were 40 kV and 40mA respectively

The surface chemical analysis of the samples was madeby X-ray Photoelectron Spectroscopy (AXIS His KratosAnalytical) using MgK120572 X-ray source (ℎ120592 = 12536 eV)and an analyzer pass energy of 40 eV The physical adsorp-tion of nitrogen was performed on a NOVA 1000 system(Quantachrome) at 77K Surface areas of the samples werecalculated based on the BET model

The DRS spectra of all the samples were recorded todetermine the samplersquos UV-VIS light absorption capacityon a Jasco-V650 diode array computer controlled (withSpectraManager software) spectrophotometer equipped withan ILV-724 integration sphere The recorded spectral datawas acquired in the 220ndash800 nm range with 05 nm datapitch and 100 nmmin scan speed When higher resolutionof the spectra was needed (usually in the 400ndash525 nm) thedata pitch was changed to 005 nm and the scan speed to50 nmmin

SEM-EDX analysis was performed to evaluate the mor-phology of the amorphous starting material and the obtainedwell crystallized catalysts on a Hitachi S-4700 Type II coldfield emission scanning electron microscope equipped witha Rontec QX2-EDS spectrometer

23 Photoreactor The experiments were performed in anannular photoreactor with a separate immersion well for thevisible lamp The lamps were cooled using circulating waterThe reactorwas of 500mL capacityThe sampleswere taken atknown intervals of time and absorbance was measured usingUV-spectrophotometer

24 Preparation of Catalyst Titanium dioxide was preparedby solgel method using Titanium isopropoxide as precursorTitanium dioxide sol was prepared using Titanium iso-propoxide as precursor 8mL of Titanium isopropoxide wasmixed with 42mL of ethanol and stirred well To this 100mLof 50 ethanol was added slowly and continuously stirred for30min at a temperature of 80∘C for the hydrolysis reactionto take place a method modified and adopted from Saif andAbdel-Mottaleb [17] A modified method was adopted forCerium sol preparation from Alouche [18] 65 g of Ceriumnitrate was dissolved in 1 L of glacial acetic acidThis solutionwas added to 1 L of 10 ammonia This is the sol of CeriumThis sol was then added to TiO

2sol and stirred uniformly and

continuously It was then left for ageing for 24 hours and thencalcined at 400∘C for 4 hours This catalyst is referred to asTiO2-Ce

International Journal of Photoenergy 3

140120100

80604020

0160140120100

80604020

010 20 30 40 50 60 70

Inte

nsity

(CPS

)In

tens

ity (C

PS) Ti

Ti

Ce

Ce

TiO2-Ce

TiO2 (solgel)

2120579 (deg)

Figure 1 XRD analysis of TiO2and TiO

2-Ce

25 Degradation Experiment The batch degradation exper-iment was performed in an annular photoreactor by takinga known quantity of catalyst to aqueous solution of concen-trations ranging between 25 and 200mg Lminus1 Visible light of150W 300W and 500W was used for degradation and thesolution was irradiated for 7 hours Samples were collectedat different intervals of time and the solution was analysedfor concentration of nitrobenzene by reading the absorbanceat 2645 nm in an UV spectrophotometer The percentagedegradation was the reduction in concentration compared tothe original concentration as given in

Percentage degradation =1198620minus 119862

1198620

lowast 100 (1)

where 1198620is the initial concentration of the aqueous solution

and 119862 is the concentration at any time 119905 The unknownconcentration of the solution at any time can be predictedfrom the standard plot of absorbance and concentration ofthe solution

3 Results and Discussion

31 Catalyst Characterization XRD patterns were recordedfor the prepared and calcined samples on a graphite crystalmonochromator operating with a Cu anode and a sealedX-ray tube as shown in Figure 1 For the range of 20ndash80∘with 005∘ step size the 2120579 scans were recorded at severalresolutions using CuK

120572radiation of wavelength 154 A Aver-

age particle size was determined by using full width at halfmaximum (FWHM) data Schererrsquos formula (2) was used todetermine average particle size as follows

119863 =119896120582

120573Cos 120579 (2)

where 119863 is the diameter of the particle 119896 is a constant equalto 089 120582 is the X-ray wavelength equal to 0154 nm 120573 isthe full width at half maximum and 120579 is the half diffractionangle [4] The XRD pattern of solgel-TiO

2showed primary

Table 1 Physical characterization of the catalysts

Catalyst 119878BETm2 gminus1

Pore volumecm3 gminus1

Paricle diameter nmSchererrsquosformula Using 119878BET

TiO2 (solgel) 102 034 1321 1401TiO2-Ce 92 020 1914 2004

anatase peaks at 2506∘ 4754∘ 5446∘ and 6172∘ The rutilephase of solgel-TiO

2was indicated by the peaks 374∘ and

5363∘ Titanium dioxide in the anatase form is generallyaccepted to be the most active polymorph [19] This betterefficiency is attributed to a higher degree of hydroxylationof anatase when compared with that of the rutile phase TheXRDpatterns ofCe dopedTiO

2samples almost coincidewith

those of pure solgel-TiO2but show diffraction peaks due to

cerium doping The average particle sizes of solgel-TiO2and

TiO2-Ce were calculated and tabulated in Table 1

The particle size was also calculated using surface areacalculated fromBET isotherms determined using BETQuan-tachrome instruments as given in (3) The surface areaaverage pore area and particle size calculated are shown inTable 1 Consider the following

Particle Diameter 119863 = 6000119878BET (3)

where 119878BET is the surface area (cm2 gminus1) and 120588 is the densityof the catalyst which is approximately 42 gcmminus3 for titaniabased particles The ionic radii of Ce3+ and Ti2+ are 0101 nmand 0068 nm respectively Ce3+ could not be incorporatedinto the lattice of TiO

2and hence there was an increase in

particle size As the particle size increases the surface areadecreases as seen from Table 1

The valence state of Cerium in the TiO2-Ce sample was

examined by XPS The XP spectrum in Figure 2 showsthe characteristic Ce 3d peak that has a binding energy of8873 eV XPS peaks corresponding to Ce4+ ion were notfound This result confirms the presence of Cerium depositson the TiO

2surface of the TiO

2-Ce sample The binding

energies for Ti 2p were 4583 eV and 4641 eV as shownin Figure 2 Combined with the XRD analysis it could beunderstood that the doping cerium atoms presented in theforms of Ce

2O3and were distributed on the surface of titania

Figure 3 shows SEM photograph of the typical samplesof TiO

2(a) and TiO

2-Ce (b) From the image the sample

TiO2-Ce existed approximately in the form of spherical

particle and presented porous structures similar to those ofTiO2 According to the statistical estimation the average

size was about 145 nm which was in accordance with thevalue determined by XRD (1914 nm) The morphologicalstudy shows that for both TiO

2and TiO

2-Ce catalyst the

surface looked almost the same with slightly whitish portionindicating the deposition of Ce On the basis of the SEMresults the Ti Ka-fluorescence signals for the pure TiO

2and

TiO2-Ce samples were also obtained by EDX analysis and the

spectra are shown in Figure 4 which gave both qualitative

4 International Journal of Photoenergy

875 880 885 890 895

Inte

nsity

(au

)

Binding energy (eV)

Ce 3d

8873 eV

(a)

Inte

nsity

(au

)

Binding energy (eV)454 458 462 466 470 474

Ti 2p

4585 eV

4645 eV

(b)

Figure 2 XPS analysis of TiO2-Ce doped catalyst

(a) (b)

Figure 3 SEM analysis of TiO2(a) and TiO

2-Ce (b) doped catalyst

3000

2000

1000

00 1 2 3 4 5

TiO2-Ce

OTi

Ce Ti

OTi

Ce Ti

(keV)

Full scale counts 3320

(a)

0 1 2 3 4 5

OTi

Ti

Ti

TiO2

2500

2000

1500

1000

500

0

OTi

Ti

Ti

(keV)klm-80-Hg

(b)

Figure 4 EDX analysis of TiO2-Ce doped and TiO

2catalyst

International Journal of Photoenergy 5

Table 2 Catalyst composition using EDX analysis of TiO2 andTiO2-Ce catalyst

Element Compound TiO2 TiO2-Ce

O 1183 1965Ti 8817 7656Ce mdash 379

and quantitative information about the elemental and atomicpercentages in the TiO

2and TiO

2-Ce samples as presented

in Table 2In order to estimate the band gap distance UV-vis

spectroscopy was employed An Oriel Instruments spec-trometer with an integrating sphere was used for UV-Visspectrometry measurements to analyze the red-shifts in theabsorption regionsTheUV-Vis transmittancemeasurementswere taken and converted into absorption readings as given inFigure 5 For pure TiO

2 the band gap energy correpsonding

to 3888 nm indicates 318 eV which was found to be inaccordance with that of other researchers [20ndash22] while forTiO2-Ce the band gap energy reduced due to the shift of

absorbance further away from UV region The band gapenergy corresponding to the wavelength of 5514 nm wasdetermined to be 225 eV The results show that cerium doesimprove visible light absorbance of TiO

2due to cerium

plasmon absorption

32 Control Experiment Photocatalytic degradation studieswere performed using TiO

2-Ce and compared with undoped

TiO2 The catalyst dosage was uniformly taken to be 01 g Lminus1

for all the experiments with solution concentration to be50mg Lminus1 pH of 68 and different light intensities (150 300and 500W) From Figure 6 it could be seen that using TiO

2-

Ce and 500W light the degradation achieved was 7909whichwas higher than the other catalysts studied Addition ofCerium to TiO

2has increased the percentage of degradation

by 14 when compared to TiO2 The photolytic degradation

of nitrobenzene was performed in the absence of the catalystvarying the intensity of the visible light for comparing theperformance of cerium doped catalyst as shown in Figure 6The degradation using 150 300 and 500W was found to be23 25 and 29 respectively This was much lower than thedegradation using Cerium doped catalyst

Though the particle size of TiO2-Ce was higher than

TiO2(solgel) it showed better degradation because in photo-

catalysis doping a semiconductor changed the photocatalyticprocess by suppressing electron-hole recombination andwhen the electron formed due to excitation migrates to themetal it gets trapped withinThe organic compound diffusesto the free hole on the semiconductor surface and oxidationof nitrobenzene occurs The presence of cerium species onTiO2influences the photoreactivity by altering the electron-

hole pair recombination rate through the following equations(4)ndash(7) The reduction in band gap energy from 32 eV to

300 350 400 450 500 550 600 650 700

Abso

rban

ce (a

u)

Wavelength (nm)

Ti-CeTiO2 (solgel)

Figure 5 UV-DRIFT analysis of TiO2and TiO

2-Ce catalyst

231

6

251

8

289

4

591

5

620

1

651

4

689

8

711

6 791

4

208

4

226

6

260

5

544

1

573

6

601

3

651

9

663

2 728

9

0102030405060708090

Degradation ()TOC removal ()

Phot

olys

is (150

W)

Phot

olys

is (300

W)

Phot

olys

is (500

W)

TiO

2(s

olge

l)(150

W)

TiO

2(s

olge

l)(300

W)

TiO

2(s

olge

l)(500

W)

TiO

2-C

e (150

W)

TiO

2-C

e (300

W)

TiO

2-C

e (500

W)

Figure 6 Degradation of NB for different catalysts at differentintensities (Conc 50mg Lminus1 pH 68 and catalyst dosage 01 g Lminus1)

225 eV also contributed to this increase in degradationConsider

Ce3+ +O2997888rarr∙Ominus2 + Ce4+ (4)

Ce4+ + eminus 997888rarr Ce3+ (5)

Ce3+ + TiO2+ ℎ] 997888rarr eminus + h+ (6)

Ce2O3+ ℎ] 997888rarr eminus + h+ (7)

The present study revealed that the cerium doped TiO2in

sol-sol method could be effectively used as compared to othercatalysts as discussed in Table 3 Better shift of the catalysttowards visible region has resulted in 100 degradation ata pH of 9 and catalyst dosage of 01 gLminus1 (as summarized inSection 335)

6 International Journal of Photoenergy

Table 3 Comparison of the performance of the present work with other published works

Catalyst Properties Light source degradation Reference

Ce doped TiO2

Particle size 108 nmSurface area 896m2gminus1

Band gap 368 nmVisible 5 for 50mgLminus1 of

NB solutionAlouche (2008)

[18]

H3PW12O40-TiO2 Visible 941 of 20mgLminus1 ofNB solution in 65 hrs

Tayade et al(2007) [19]

Fe-ETS-10 Surface area 191m2gminus1Band gap 313 eV UV 43 of 50mgLminus1 of

NB solution in 4 hrsShen et al(2009) [20]

NanocrystallineTiO2

Particle size 12 nmSurface area 166m2gminus1

Band gap 328 eVVisible 96 of 50mgLminus1 of

NB solution in 8 hrsTayade et al(2006) [6]

Silver metalexchanged ETS-10Zeolite

Surface area 205m2gminus1Band gap 316 eV UV light (267 nm) 57 50mgLminus1 of NB

solution in 4 hrsShen et al(2009) [20]

N-Ce doped TiO2

Particle size 108 nmSurface area 152m2gminus1

Band gap 219 eVVisible (300W xenon lamp) 53 50mgLminus1 of NB

solution in 4 hrsAlouche (2008)

[18]

The TOC removal was studied for different intervalsof time The photomineralization of the compounds weremeasured using Total Organic Carbon analyzer (ShimadzuTOC 5000A) The extent of TOC removal was comparedwith the undoped and Cerium doped TiO

2catalystThe TOC

removal was maximum using Cerium doped catalyst at anintensity of 500W

33 Optimization of Operational Parameters

331 Effect of Solution Concentration The most importantoperational parameter to be studied is the influence of initialconcentration of the solution NB photocatalytic degradationstudies were carried out using 25ndash200mg Lminus1 initial concen-tration of NB and 01 g Lminus1 of catalyst loading The plot ofdegradation for different solution concentration was madeand from Figure 7 it could be inferred that as concentrationincreased percentage degradation decreased This may bedue to the fact that with the increase in initial concentrationof NB while the irradiation period and catalyst dose arekept constant more NB molecules are present on the surfaceof TiO

2 Thus an increase in the number of substrate ions

accommodating in interlayer spacing inhibits the action ofthe catalyst which thereby decreases the number of reactive∙OH and O∙minus

2free radicals attacking the NB molecules and

hence lowers the photodegradation efficiency [23]

332 Effect of Light Intensity The influence of light intensityon the degradation efficiency has been examined at constantNitrobenzene concentration (50mg Lminus1) at pH (65) andcatalyst loading (01 g Lminus1) It is evident that the degradationrate increases with increase in the light intensity as shownin Figure 6 The photons required for the electron transferwere generated by UV irradiation which results in electrontransfer fromvalence band to conduction bandof the catalystThe degradation increases when more radiations fall on

0

10

20

30

40

50

60

70

80

90

050 100 150 200 250 300 350 400

Deg

rada

tion

()

Time (min)

25mgLminus1

75mgLminus1

150mgLminus1

50mgLminus1

100mgLminus1

200mgLminus1

Figure 7 Effect of solution concentration on degradation (lightintensity 500W pH 68 and catalyst dosage 01 g Lminus1)

the catalyst surface and hence more hydroxyl radicals areproduced [24]

333 Effect of Catalyst Dosage Photocatalyst dosage addedto the reaction vessel is a major parameter affecting thephotocatalytic degradation efficiency The aqueous solutionof 50mg Lminus1 of solution was degraded using different catalystdosages (0025 005 01 015 and 02 g Lminus1) From Figure 8it can be seen that maximum degradation was achieved forthe catalyst dosage of 01 g Lminus1 It could also be inferred thatfurther increase in catalyst dosage did not yield an increasein degradation percentage

International Journal of Photoenergy 7

68

70

72

74

76

78

80

0 005 01 015 02 025

Deg

rada

tion

()

Catalyst dosage (gLminus1)

Figure 8 Effect of catalyst dosage on degradation (Conc50mg Lminus1 pH 68 and intensity 500W)

The increase in degradation percentage for 0025 to01 g Lminus1 may be due to an increase in the amount of activesites on the surface of the photocatalyst particlesThe numberof NB molecules adsorbed as well as the number of photonsabsorbed increase with the increase in catalyst concentrationthereby enhancing the rate of degradation Addition ofcatalyst beyond 01 g Lminus1 leads to decrease in the degradationAggregation of TiO

2particles occurs at higher dosage causing

decrease in the number of surface active sites and also there isan increase in the opacity of the solution and light scatteringof TiO

2particles at high dosage through the solution [25]

334 Effect of pH of the Solution pH of the solution greatlyinfluences the degradation rate It tends to change the surfaceproperty of the catalyst The effect of change in initial pH(2 4 65 8 9 10 and 11) of 50mg Lminus1 of the nitrobenzenesolution was studied by adding 01 g Lminus1 of catalyst The plotof degradation against pH (Figure 9) showed that as pHincreased the degradation increased A maximum of 100degradation was achieved at pH 9The degradation was lowerin lower acidic and higher alkaline pH

pH of the catalyst dispersions majorly affects the surfaceproperties on the particles agglomerate size formed andthe conductance and valence bands positions [26] Thenitrobenzene solution was degraded by hydroxyl attack anddirect oxidation at the holes and reduction at the conductionband In alkaline pH the surface of TiO

2-Ce acquires a

negative charge leading to greater adsorption and henceincreasing the degradation rate in the alkaline media

335 Kinetic Modelling Using Langmuir Hinshelwood ModelThe degradation percentage was calculated and for hetero-geneous catalyst the Langmuir Hinshelwood model wasused to calculate the apparent rate constant The LangmuirHinshelwoodmodel derived based on themonolayer activityassumption was used to estimate the kinetic parameters in

72

74

76

78

80

82

84

86

0 2 4 6 8 10 12

Deg

rada

tion

()

Solution pH

Figure 9 Effect of solution pH on degradation (Conc 50mg Lminus1catalyst dosage 01 g Lminus1 and intensity 500W)

0

02

04

06

08

1

12

14

16

18

2

0 50 100 150 200 250 300 350 400Time (min)

25mgLminus1

75mgLminus1150mgLminus150mgLminus1100mgLminus1

200mgLminus1

ln(C

0C

)

Figure 10 Langmuir Hinshelwood plot (pH 68 catalyst dosage01 g Lminus1 and light intensity 500W)

terms of reaction rate constant (119896119903) and Langmuir Hinshel-

wood adsorption constant (119870LH) which is as given in

119903 =119896119903119870LH119862

1 + 119870LH1198620= 119896app119862 (8)

where is rate of disappearance of organic substratemg Lminus1minminus1 and 119862 is concentration of organic substratemg Lminus1

119896app =119896119903119870LH

1 + 119870LH1198620 (9)

Linearization of (8) yields an equation from which a plotof ln (119862

0119862) against time will result in a linear relation-

ship resulting in zero intercept and apparent rate constant(119896app) derived from the slope of the line Figure 10 is the

8 International Journal of Photoenergy

0

01

02

03

04

05

06

0 0001 0002 0003 0004 0005 0006

times10minus2

kap

p(m

inminus1) (

theo

)

kapp (minminus1) (exp)

Figure 11 Comparison between the experimental and theoreticalvalues of apparent rate constant

representation of the plot from which the apparent rateconstant was determined using slope of the line Similarlyfor all the conditions of pH (2ndash11) concentration (25ndash200mg Lminus1) catalyst dosage (0025ndash02 g Lminus1) and intensityof visible light (150ndash500W) the plot of ln (119862

0119862) against

time was evaluated The apparent rate constant was foundto increase with light intensity and decrease with solutionconcentrationThemaximum degradation could be achievedat the following parameter condition pH 9 dosage 01 g Lminus1solution concentration 25mg Lminus1 and light intensity 500WThe nonlinear fit between the apparent rate constant and theoperational parameters was determined and were found thatthe experimental values when compared with the theoreticalvalues as in Figure 11 the theoretical values had less than 3error and hence the following equation (10) could be chosenfor approximating the experimental conditions Equation(10) could be used for a condition of pH 2 to 9 dosageof 005 to 01 g Lminus1 light intensity of 150 300 or 500Wand concentration of solution from 25 to 200mg Lminus1 Thenonlinear equation was

119896app (theoretical)

= 0000229 lowast Intensity0584 lowast Concentrationminus0230

lowast Dosage0425 lowast pH0336(10)

4 Conclusion

The undoped and cerium doped titania photocatalyst wasprepared through the sol-gel route The cerium doped pho-tocatalyst could absorb the visible light and showed highphotoactivity in the visible region because of the band gapnarrowing Cerium atoms existed in the state of Ce

2O3

and were dispersed on the surface of titania suppressingthe recombination of electron-hole pairs and increasing thephotoactivity as confirmed using XPS and DRIFT analysis

The average crystal size and the surface area were deter-mined and compared between two types of catalysts Theoperational parameters were optimized and the followingcondition was suggested to obtain maximum degradationpH 9 dosage 01 g Lminus1 solution concentration 25mg Lminus1and light intensity 500W The kinetic study revealed thatthe degradation followed Langmuir Hinshelwood modelThe apparent rate constant was determined and evaluatedtheoretically using the nonlinear fit which depends on theoperational parameters Based on the previously mentionedexperiments and characterization it could be concluded thatCeriumdoped TiO

2catalyst prepared by solgelmethod could

be efficiently used for degradation of Nitrobenzene usingvisible light

References

[1] S C Moon H Mametsuka S Tabata and E Suzuki ldquoPhoto-catalytic production of hydrogen from water using TiO

2and

BTiO2rdquo Catalysis Today vol 58 no 2 pp 125ndash132 2000

[2] C Lettmann K Hildenbrand H Kisch W Macyk and WF Maier ldquoVisible light photodegradation of 4-chlorophenolwith a coke-containing titaniumdioxide photocatalystrdquoAppliedCatalysis B vol 32 no 4 pp 215ndash227 2001

[3] 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

[4] C-S Wu and C Chen ldquoA visible-light response vanadium-doped titania nanocatalyst by sol-gel methodrdquo Journal of Photo-chemistry and Photobiology A vol 163 no 3 pp 509ndash515 2004

[5] T Umebayashi T Yamaki S Tanaka and K Asai ldquoVisiblelight-induced degradation ofmethylene blue on S-doped TiO

2rdquo

Chemistry Letters vol 32 no 4 pp 330ndash331 2003[6] R J Tayade R G Kulkarni and R V Jasra ldquoPhotocatalytic

degradation of aqueous nitrobenzene by nanocrystalline TiO2rdquo

Industrial and Engineering Chemistry Research vol 45 no 3 pp922ndash927 2006

[7] M H Priya and G Madras ldquoPhotocatalytic degradation ofnitrobenzenes with combustion synthesized nano-TiO

2rdquo Jour-

nal of Photochemistry and Photobiology A vol 178 no 1 pp 1ndash72006

[8] S Ikeda N Sugiyama B Pal et al ldquoPhotocatalytic activityof transition-metal-loaded titanium(IV) oxide powders sus-pended in aqueous solutions correlation with electron-holerecombination kineticsrdquo Physical Chemistry Chemical Physicsvol 3 no 2 pp 267ndash273 2001

[9] A Fuerte M D Hernandez-Alonso A J Maira et al ldquoVisiblelight-activated nanosized doped-TiO

2photocatalystsrdquo Chemi-

cal Communications no 24 pp 2718ndash2719 2001[10] W Choi A Termin and M R Hoffmann ldquoThe role of

metal ion dopants in quantum-sized TiO2 correlation between

photoreactivity and charge carrier recombination dynamicsrdquoJournal of Physical Chemistry vol 98 no 51 pp 13669ndash136791994

[11] B M Reddy P M Sreekanth Y Yamada Q Xu and TKobayashi ldquoSurface characterization of sulfate molybdate andtungstate promoted TiO

2-ZrO2solid acid catalysts by XPS and

other techniquesrdquoApplied Catalysis A vol 228 no 1-2 pp 269ndash278 2002

International Journal of Photoenergy 9

[12] VMOrera R IMerino and F Pena ldquoCe3+harrCe4+ conversionin ceria-doped zirconia single crystals induced by oxido-reduction treatmentsrdquo Solid State Ionics vol 72 no 2 pp 224ndash231 1994

[13] W M Yen M Raukas S A Basun W Van Schaik and UHappek ldquoOptical and photoconductive properties of cerium-doped crystalline solidsrdquo Journal of Luminescence vol 69 no5-6 pp 287ndash294 1996

[14] S W Chen J M Lee K T Lu et al ldquoBand-gap narrowingof TiO

2doped with Ce probed with x-ray absorption spec-

troscopyrdquo Applied Physics Letters vol 97 no 1 Article ID012104 2010

[15] H Liu X Z Li Y J Leng andW Z Li ldquoAn alternative approachto ascertain the rate-determining steps of TiO

2photoelectro-

catalytic reaction by electrochemical impedance spectroscopyrdquoJournal of Physical Chemistry B vol 107 no 34 pp 8988ndash89962003

[16] D S Bhatkhande V G Pangarkar and A A C M BeenackersldquoPhotocatalytic degradation of nitrobenzene using titaniumdioxide and concentrated solar radiation chemical effects andscaleuprdquoWater Research vol 37 no 6 pp 1223ndash1230 2003

[17] M Saif and M S A Abdel-Mottaleb ldquoTitanium dioxidenanomaterial dopedwith trivalent lanthanide ions of Tb Eu andSm preparation characterization and potential applicationsrdquoInorganica Chimica Acta vol 360 no 9 pp 2863ndash2874 2007

[18] A Alouche ldquoPreparation and characterization of Copper andor Cerium catalysts supported on Alumina or Ceriardquo JordanJournal of Mechanical and Industrial Engineering vol 2 pp 111ndash116 2008

[19] R J Tayade P K Surolia R G Kulkarni and R V JasraldquoPhotocatalytic degradation of dyes and organic contaminantsin water using nanocrystalline anatase and rutile TiO

2rdquo Science

and Technology of AdvancedMaterials vol 8 no 6 pp 455ndash4622007

[20] X-Z Shen Z-C Liu S-M Xie and J Guo ldquoDegradationof nitrobenzene using titania photocatalyst co-doped withnitrogen and cerium under visible light illuminationrdquo Journalof Hazardous Materials vol 162 no 2-3 pp 1193ndash1198 2009

[21] WWang Y Huang and S Yang ldquoPhotocatalytic degradation ofnitrobenzene wastewater with H

3PW12O40TiO2rdquo in Proceed-

ings of the International Conference on Mechanic Automationand Control Engineering (MACE rsquo10) pp 1303ndash1305 June 2010

[22] P K Surolia R J Tayade and R V Jasra ldquoPhotocatalytic degra-dation of nitrobenzene in an aqueous system by transition-metal-exchanged ETS-10 zeolitesrdquo Industrial and EngineeringChemistry Research vol 49 no 8 pp 3961ndash3966 2010

[23] W Bahnemann M Muneer and M M Haque ldquoTitaniumdioxide-mediated photocatalysed degradation of few selectedorganic pollutants in aqueous suspensionsrdquoCatalysis Today vol124 no 3-4 pp 133ndash148 2007

[24] A E Cassano and O M Alfano ldquoReaction engineering of sus-pended solid heterogeneous photocatalytic reactorsrdquo CatalysisToday vol 58 no 2 pp 167ndash197 2000

[25] A A Adesina ldquoIndustrial exploitation of photocatalysis pro-gress perspectives and prospectsrdquo Catalysis Surveys from Asiavol 8 no 4 pp 265ndash273 2004

[26] Y Ku and C B Hsieh ldquoPhotocatalytic decomposition of 24-dichlorophenol in aqueous TiO

2suspensionsrdquoWater Research

vol 26 no 11 pp 1451ndash1456 1992

Impact Factor 173028 Days Fast Track Peer ReviewAll Subject Areas of ScienceSubmit at httpwwwtswjcom

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawi Publishing Corporation httpwwwhindawicom Volume 2013

The Scientific World Journal

International Journal of Photoenergy 3

140120100

80604020

0160140120100

80604020

010 20 30 40 50 60 70

Inte

nsity

(CPS

)In

tens

ity (C

PS) Ti

Ti

Ce

Ce

TiO2-Ce

TiO2 (solgel)

2120579 (deg)

Figure 1 XRD analysis of TiO2and TiO

2-Ce

25 Degradation Experiment The batch degradation exper-iment was performed in an annular photoreactor by takinga known quantity of catalyst to aqueous solution of concen-trations ranging between 25 and 200mg Lminus1 Visible light of150W 300W and 500W was used for degradation and thesolution was irradiated for 7 hours Samples were collectedat different intervals of time and the solution was analysedfor concentration of nitrobenzene by reading the absorbanceat 2645 nm in an UV spectrophotometer The percentagedegradation was the reduction in concentration compared tothe original concentration as given in

Percentage degradation =1198620minus 119862

1198620

lowast 100 (1)

where 1198620is the initial concentration of the aqueous solution

and 119862 is the concentration at any time 119905 The unknownconcentration of the solution at any time can be predictedfrom the standard plot of absorbance and concentration ofthe solution

3 Results and Discussion

31 Catalyst Characterization XRD patterns were recordedfor the prepared and calcined samples on a graphite crystalmonochromator operating with a Cu anode and a sealedX-ray tube as shown in Figure 1 For the range of 20ndash80∘with 005∘ step size the 2120579 scans were recorded at severalresolutions using CuK

120572radiation of wavelength 154 A Aver-

age particle size was determined by using full width at halfmaximum (FWHM) data Schererrsquos formula (2) was used todetermine average particle size as follows

119863 =119896120582

120573Cos 120579 (2)

where 119863 is the diameter of the particle 119896 is a constant equalto 089 120582 is the X-ray wavelength equal to 0154 nm 120573 isthe full width at half maximum and 120579 is the half diffractionangle [4] The XRD pattern of solgel-TiO

2showed primary

Table 1 Physical characterization of the catalysts

Catalyst 119878BETm2 gminus1

Pore volumecm3 gminus1

Paricle diameter nmSchererrsquosformula Using 119878BET

TiO2 (solgel) 102 034 1321 1401TiO2-Ce 92 020 1914 2004

anatase peaks at 2506∘ 4754∘ 5446∘ and 6172∘ The rutilephase of solgel-TiO

2was indicated by the peaks 374∘ and

5363∘ Titanium dioxide in the anatase form is generallyaccepted to be the most active polymorph [19] This betterefficiency is attributed to a higher degree of hydroxylationof anatase when compared with that of the rutile phase TheXRDpatterns ofCe dopedTiO

2samples almost coincidewith

those of pure solgel-TiO2but show diffraction peaks due to

cerium doping The average particle sizes of solgel-TiO2and

TiO2-Ce were calculated and tabulated in Table 1

The particle size was also calculated using surface areacalculated fromBET isotherms determined using BETQuan-tachrome instruments as given in (3) The surface areaaverage pore area and particle size calculated are shown inTable 1 Consider the following

Particle Diameter 119863 = 6000119878BET (3)

where 119878BET is the surface area (cm2 gminus1) and 120588 is the densityof the catalyst which is approximately 42 gcmminus3 for titaniabased particles The ionic radii of Ce3+ and Ti2+ are 0101 nmand 0068 nm respectively Ce3+ could not be incorporatedinto the lattice of TiO

2and hence there was an increase in

particle size As the particle size increases the surface areadecreases as seen from Table 1

The valence state of Cerium in the TiO2-Ce sample was

examined by XPS The XP spectrum in Figure 2 showsthe characteristic Ce 3d peak that has a binding energy of8873 eV XPS peaks corresponding to Ce4+ ion were notfound This result confirms the presence of Cerium depositson the TiO

2surface of the TiO

2-Ce sample The binding

energies for Ti 2p were 4583 eV and 4641 eV as shownin Figure 2 Combined with the XRD analysis it could beunderstood that the doping cerium atoms presented in theforms of Ce

2O3and were distributed on the surface of titania

Figure 3 shows SEM photograph of the typical samplesof TiO

2(a) and TiO

2-Ce (b) From the image the sample

TiO2-Ce existed approximately in the form of spherical

particle and presented porous structures similar to those ofTiO2 According to the statistical estimation the average

size was about 145 nm which was in accordance with thevalue determined by XRD (1914 nm) The morphologicalstudy shows that for both TiO

2and TiO

2-Ce catalyst the

surface looked almost the same with slightly whitish portionindicating the deposition of Ce On the basis of the SEMresults the Ti Ka-fluorescence signals for the pure TiO

2and

TiO2-Ce samples were also obtained by EDX analysis and the

spectra are shown in Figure 4 which gave both qualitative

4 International Journal of Photoenergy

875 880 885 890 895

Inte

nsity

(au

)

Binding energy (eV)

Ce 3d

8873 eV

(a)

Inte

nsity

(au

)

Binding energy (eV)454 458 462 466 470 474

Ti 2p

4585 eV

4645 eV

(b)

Figure 2 XPS analysis of TiO2-Ce doped catalyst

(a) (b)

Figure 3 SEM analysis of TiO2(a) and TiO

2-Ce (b) doped catalyst

3000

2000

1000

00 1 2 3 4 5

TiO2-Ce

OTi

Ce Ti

OTi

Ce Ti

(keV)

Full scale counts 3320

(a)

0 1 2 3 4 5

OTi

Ti

Ti

TiO2

2500

2000

1500

1000

500

0

OTi

Ti

Ti

(keV)klm-80-Hg

(b)

Figure 4 EDX analysis of TiO2-Ce doped and TiO

2catalyst

International Journal of Photoenergy 5

Table 2 Catalyst composition using EDX analysis of TiO2 andTiO2-Ce catalyst

Element Compound TiO2 TiO2-Ce

O 1183 1965Ti 8817 7656Ce mdash 379

and quantitative information about the elemental and atomicpercentages in the TiO

2and TiO

2-Ce samples as presented

in Table 2In order to estimate the band gap distance UV-vis

spectroscopy was employed An Oriel Instruments spec-trometer with an integrating sphere was used for UV-Visspectrometry measurements to analyze the red-shifts in theabsorption regionsTheUV-Vis transmittancemeasurementswere taken and converted into absorption readings as given inFigure 5 For pure TiO

2 the band gap energy correpsonding

to 3888 nm indicates 318 eV which was found to be inaccordance with that of other researchers [20ndash22] while forTiO2-Ce the band gap energy reduced due to the shift of

absorbance further away from UV region The band gapenergy corresponding to the wavelength of 5514 nm wasdetermined to be 225 eV The results show that cerium doesimprove visible light absorbance of TiO

2due to cerium

plasmon absorption

32 Control Experiment Photocatalytic degradation studieswere performed using TiO

2-Ce and compared with undoped

TiO2 The catalyst dosage was uniformly taken to be 01 g Lminus1

for all the experiments with solution concentration to be50mg Lminus1 pH of 68 and different light intensities (150 300and 500W) From Figure 6 it could be seen that using TiO

2-

Ce and 500W light the degradation achieved was 7909whichwas higher than the other catalysts studied Addition ofCerium to TiO

2has increased the percentage of degradation

by 14 when compared to TiO2 The photolytic degradation

of nitrobenzene was performed in the absence of the catalystvarying the intensity of the visible light for comparing theperformance of cerium doped catalyst as shown in Figure 6The degradation using 150 300 and 500W was found to be23 25 and 29 respectively This was much lower than thedegradation using Cerium doped catalyst

Though the particle size of TiO2-Ce was higher than

TiO2(solgel) it showed better degradation because in photo-

catalysis doping a semiconductor changed the photocatalyticprocess by suppressing electron-hole recombination andwhen the electron formed due to excitation migrates to themetal it gets trapped withinThe organic compound diffusesto the free hole on the semiconductor surface and oxidationof nitrobenzene occurs The presence of cerium species onTiO2influences the photoreactivity by altering the electron-

hole pair recombination rate through the following equations(4)ndash(7) The reduction in band gap energy from 32 eV to

300 350 400 450 500 550 600 650 700

Abso

rban

ce (a

u)

Wavelength (nm)

Ti-CeTiO2 (solgel)

Figure 5 UV-DRIFT analysis of TiO2and TiO

2-Ce catalyst

231

6

251

8

289

4

591

5

620

1

651

4

689

8

711

6 791

4

208

4

226

6

260

5

544

1

573

6

601

3

651

9

663

2 728

9

0102030405060708090

Degradation ()TOC removal ()

Phot

olys

is (150

W)

Phot

olys

is (300

W)

Phot

olys

is (500

W)

TiO

2(s

olge

l)(150

W)

TiO

2(s

olge

l)(300

W)

TiO

2(s

olge

l)(500

W)

TiO

2-C

e (150

W)

TiO

2-C

e (300

W)

TiO

2-C

e (500

W)

Figure 6 Degradation of NB for different catalysts at differentintensities (Conc 50mg Lminus1 pH 68 and catalyst dosage 01 g Lminus1)

225 eV also contributed to this increase in degradationConsider

Ce3+ +O2997888rarr∙Ominus2 + Ce4+ (4)

Ce4+ + eminus 997888rarr Ce3+ (5)

Ce3+ + TiO2+ ℎ] 997888rarr eminus + h+ (6)

Ce2O3+ ℎ] 997888rarr eminus + h+ (7)

The present study revealed that the cerium doped TiO2in

sol-sol method could be effectively used as compared to othercatalysts as discussed in Table 3 Better shift of the catalysttowards visible region has resulted in 100 degradation ata pH of 9 and catalyst dosage of 01 gLminus1 (as summarized inSection 335)

6 International Journal of Photoenergy

Table 3 Comparison of the performance of the present work with other published works

Catalyst Properties Light source degradation Reference

Ce doped TiO2

Particle size 108 nmSurface area 896m2gminus1

Band gap 368 nmVisible 5 for 50mgLminus1 of

NB solutionAlouche (2008)

[18]

H3PW12O40-TiO2 Visible 941 of 20mgLminus1 ofNB solution in 65 hrs

Tayade et al(2007) [19]

Fe-ETS-10 Surface area 191m2gminus1Band gap 313 eV UV 43 of 50mgLminus1 of

NB solution in 4 hrsShen et al(2009) [20]

NanocrystallineTiO2

Particle size 12 nmSurface area 166m2gminus1

Band gap 328 eVVisible 96 of 50mgLminus1 of

NB solution in 8 hrsTayade et al(2006) [6]

Silver metalexchanged ETS-10Zeolite

Surface area 205m2gminus1Band gap 316 eV UV light (267 nm) 57 50mgLminus1 of NB

solution in 4 hrsShen et al(2009) [20]

N-Ce doped TiO2

Particle size 108 nmSurface area 152m2gminus1

Band gap 219 eVVisible (300W xenon lamp) 53 50mgLminus1 of NB

solution in 4 hrsAlouche (2008)

[18]

The TOC removal was studied for different intervalsof time The photomineralization of the compounds weremeasured using Total Organic Carbon analyzer (ShimadzuTOC 5000A) The extent of TOC removal was comparedwith the undoped and Cerium doped TiO

2catalystThe TOC

removal was maximum using Cerium doped catalyst at anintensity of 500W

33 Optimization of Operational Parameters

331 Effect of Solution Concentration The most importantoperational parameter to be studied is the influence of initialconcentration of the solution NB photocatalytic degradationstudies were carried out using 25ndash200mg Lminus1 initial concen-tration of NB and 01 g Lminus1 of catalyst loading The plot ofdegradation for different solution concentration was madeand from Figure 7 it could be inferred that as concentrationincreased percentage degradation decreased This may bedue to the fact that with the increase in initial concentrationof NB while the irradiation period and catalyst dose arekept constant more NB molecules are present on the surfaceof TiO

2 Thus an increase in the number of substrate ions

accommodating in interlayer spacing inhibits the action ofthe catalyst which thereby decreases the number of reactive∙OH and O∙minus

2free radicals attacking the NB molecules and

hence lowers the photodegradation efficiency [23]

332 Effect of Light Intensity The influence of light intensityon the degradation efficiency has been examined at constantNitrobenzene concentration (50mg Lminus1) at pH (65) andcatalyst loading (01 g Lminus1) It is evident that the degradationrate increases with increase in the light intensity as shownin Figure 6 The photons required for the electron transferwere generated by UV irradiation which results in electrontransfer fromvalence band to conduction bandof the catalystThe degradation increases when more radiations fall on

0

10

20

30

40

50

60

70

80

90

050 100 150 200 250 300 350 400

Deg

rada

tion

()

Time (min)

25mgLminus1

75mgLminus1

150mgLminus1

50mgLminus1

100mgLminus1

200mgLminus1

Figure 7 Effect of solution concentration on degradation (lightintensity 500W pH 68 and catalyst dosage 01 g Lminus1)

the catalyst surface and hence more hydroxyl radicals areproduced [24]

333 Effect of Catalyst Dosage Photocatalyst dosage addedto the reaction vessel is a major parameter affecting thephotocatalytic degradation efficiency The aqueous solutionof 50mg Lminus1 of solution was degraded using different catalystdosages (0025 005 01 015 and 02 g Lminus1) From Figure 8it can be seen that maximum degradation was achieved forthe catalyst dosage of 01 g Lminus1 It could also be inferred thatfurther increase in catalyst dosage did not yield an increasein degradation percentage

International Journal of Photoenergy 7

68

70

72

74

76

78

80

0 005 01 015 02 025

Deg

rada

tion

()

Catalyst dosage (gLminus1)

Figure 8 Effect of catalyst dosage on degradation (Conc50mg Lminus1 pH 68 and intensity 500W)

The increase in degradation percentage for 0025 to01 g Lminus1 may be due to an increase in the amount of activesites on the surface of the photocatalyst particlesThe numberof NB molecules adsorbed as well as the number of photonsabsorbed increase with the increase in catalyst concentrationthereby enhancing the rate of degradation Addition ofcatalyst beyond 01 g Lminus1 leads to decrease in the degradationAggregation of TiO

2particles occurs at higher dosage causing

decrease in the number of surface active sites and also there isan increase in the opacity of the solution and light scatteringof TiO

2particles at high dosage through the solution [25]

334 Effect of pH of the Solution pH of the solution greatlyinfluences the degradation rate It tends to change the surfaceproperty of the catalyst The effect of change in initial pH(2 4 65 8 9 10 and 11) of 50mg Lminus1 of the nitrobenzenesolution was studied by adding 01 g Lminus1 of catalyst The plotof degradation against pH (Figure 9) showed that as pHincreased the degradation increased A maximum of 100degradation was achieved at pH 9The degradation was lowerin lower acidic and higher alkaline pH

pH of the catalyst dispersions majorly affects the surfaceproperties on the particles agglomerate size formed andthe conductance and valence bands positions [26] Thenitrobenzene solution was degraded by hydroxyl attack anddirect oxidation at the holes and reduction at the conductionband In alkaline pH the surface of TiO

2-Ce acquires a

negative charge leading to greater adsorption and henceincreasing the degradation rate in the alkaline media

335 Kinetic Modelling Using Langmuir Hinshelwood ModelThe degradation percentage was calculated and for hetero-geneous catalyst the Langmuir Hinshelwood model wasused to calculate the apparent rate constant The LangmuirHinshelwoodmodel derived based on themonolayer activityassumption was used to estimate the kinetic parameters in

72

74

76

78

80

82

84

86

0 2 4 6 8 10 12

Deg

rada

tion

()

Solution pH

Figure 9 Effect of solution pH on degradation (Conc 50mg Lminus1catalyst dosage 01 g Lminus1 and intensity 500W)

0

02

04

06

08

1

12

14

16

18

2

0 50 100 150 200 250 300 350 400Time (min)

25mgLminus1

75mgLminus1150mgLminus150mgLminus1100mgLminus1

200mgLminus1

ln(C

0C

)

Figure 10 Langmuir Hinshelwood plot (pH 68 catalyst dosage01 g Lminus1 and light intensity 500W)

terms of reaction rate constant (119896119903) and Langmuir Hinshel-

wood adsorption constant (119870LH) which is as given in

119903 =119896119903119870LH119862

1 + 119870LH1198620= 119896app119862 (8)

where is rate of disappearance of organic substratemg Lminus1minminus1 and 119862 is concentration of organic substratemg Lminus1

119896app =119896119903119870LH

1 + 119870LH1198620 (9)

Linearization of (8) yields an equation from which a plotof ln (119862

0119862) against time will result in a linear relation-

ship resulting in zero intercept and apparent rate constant(119896app) derived from the slope of the line Figure 10 is the

8 International Journal of Photoenergy

0

01

02

03

04

05

06

0 0001 0002 0003 0004 0005 0006

times10minus2

kap

p(m

inminus1) (

theo

)

kapp (minminus1) (exp)

Figure 11 Comparison between the experimental and theoreticalvalues of apparent rate constant

representation of the plot from which the apparent rateconstant was determined using slope of the line Similarlyfor all the conditions of pH (2ndash11) concentration (25ndash200mg Lminus1) catalyst dosage (0025ndash02 g Lminus1) and intensityof visible light (150ndash500W) the plot of ln (119862

0119862) against

time was evaluated The apparent rate constant was foundto increase with light intensity and decrease with solutionconcentrationThemaximum degradation could be achievedat the following parameter condition pH 9 dosage 01 g Lminus1solution concentration 25mg Lminus1 and light intensity 500WThe nonlinear fit between the apparent rate constant and theoperational parameters was determined and were found thatthe experimental values when compared with the theoreticalvalues as in Figure 11 the theoretical values had less than 3error and hence the following equation (10) could be chosenfor approximating the experimental conditions Equation(10) could be used for a condition of pH 2 to 9 dosageof 005 to 01 g Lminus1 light intensity of 150 300 or 500Wand concentration of solution from 25 to 200mg Lminus1 Thenonlinear equation was

119896app (theoretical)

= 0000229 lowast Intensity0584 lowast Concentrationminus0230

lowast Dosage0425 lowast pH0336(10)

4 Conclusion

The undoped and cerium doped titania photocatalyst wasprepared through the sol-gel route The cerium doped pho-tocatalyst could absorb the visible light and showed highphotoactivity in the visible region because of the band gapnarrowing Cerium atoms existed in the state of Ce

2O3

and were dispersed on the surface of titania suppressingthe recombination of electron-hole pairs and increasing thephotoactivity as confirmed using XPS and DRIFT analysis

The average crystal size and the surface area were deter-mined and compared between two types of catalysts Theoperational parameters were optimized and the followingcondition was suggested to obtain maximum degradationpH 9 dosage 01 g Lminus1 solution concentration 25mg Lminus1and light intensity 500W The kinetic study revealed thatthe degradation followed Langmuir Hinshelwood modelThe apparent rate constant was determined and evaluatedtheoretically using the nonlinear fit which depends on theoperational parameters Based on the previously mentionedexperiments and characterization it could be concluded thatCeriumdoped TiO

2catalyst prepared by solgelmethod could

be efficiently used for degradation of Nitrobenzene usingvisible light

References

[1] S C Moon H Mametsuka S Tabata and E Suzuki ldquoPhoto-catalytic production of hydrogen from water using TiO

2and

BTiO2rdquo Catalysis Today vol 58 no 2 pp 125ndash132 2000

[2] C Lettmann K Hildenbrand H Kisch W Macyk and WF Maier ldquoVisible light photodegradation of 4-chlorophenolwith a coke-containing titaniumdioxide photocatalystrdquoAppliedCatalysis B vol 32 no 4 pp 215ndash227 2001

[3] 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

[4] C-S Wu and C Chen ldquoA visible-light response vanadium-doped titania nanocatalyst by sol-gel methodrdquo Journal of Photo-chemistry and Photobiology A vol 163 no 3 pp 509ndash515 2004

[5] T Umebayashi T Yamaki S Tanaka and K Asai ldquoVisiblelight-induced degradation ofmethylene blue on S-doped TiO

2rdquo

Chemistry Letters vol 32 no 4 pp 330ndash331 2003[6] R J Tayade R G Kulkarni and R V Jasra ldquoPhotocatalytic

degradation of aqueous nitrobenzene by nanocrystalline TiO2rdquo

Industrial and Engineering Chemistry Research vol 45 no 3 pp922ndash927 2006

[7] M H Priya and G Madras ldquoPhotocatalytic degradation ofnitrobenzenes with combustion synthesized nano-TiO

2rdquo Jour-

nal of Photochemistry and Photobiology A vol 178 no 1 pp 1ndash72006

[8] S Ikeda N Sugiyama B Pal et al ldquoPhotocatalytic activityof transition-metal-loaded titanium(IV) oxide powders sus-pended in aqueous solutions correlation with electron-holerecombination kineticsrdquo Physical Chemistry Chemical Physicsvol 3 no 2 pp 267ndash273 2001

[9] A Fuerte M D Hernandez-Alonso A J Maira et al ldquoVisiblelight-activated nanosized doped-TiO

2photocatalystsrdquo Chemi-

cal Communications no 24 pp 2718ndash2719 2001[10] W Choi A Termin and M R Hoffmann ldquoThe role of

metal ion dopants in quantum-sized TiO2 correlation between

photoreactivity and charge carrier recombination dynamicsrdquoJournal of Physical Chemistry vol 98 no 51 pp 13669ndash136791994

[11] B M Reddy P M Sreekanth Y Yamada Q Xu and TKobayashi ldquoSurface characterization of sulfate molybdate andtungstate promoted TiO

2-ZrO2solid acid catalysts by XPS and

other techniquesrdquoApplied Catalysis A vol 228 no 1-2 pp 269ndash278 2002

International Journal of Photoenergy 9

[12] VMOrera R IMerino and F Pena ldquoCe3+harrCe4+ conversionin ceria-doped zirconia single crystals induced by oxido-reduction treatmentsrdquo Solid State Ionics vol 72 no 2 pp 224ndash231 1994

[13] W M Yen M Raukas S A Basun W Van Schaik and UHappek ldquoOptical and photoconductive properties of cerium-doped crystalline solidsrdquo Journal of Luminescence vol 69 no5-6 pp 287ndash294 1996

[14] S W Chen J M Lee K T Lu et al ldquoBand-gap narrowingof TiO

2doped with Ce probed with x-ray absorption spec-

troscopyrdquo Applied Physics Letters vol 97 no 1 Article ID012104 2010

[15] H Liu X Z Li Y J Leng andW Z Li ldquoAn alternative approachto ascertain the rate-determining steps of TiO

2photoelectro-

catalytic reaction by electrochemical impedance spectroscopyrdquoJournal of Physical Chemistry B vol 107 no 34 pp 8988ndash89962003

[16] D S Bhatkhande V G Pangarkar and A A C M BeenackersldquoPhotocatalytic degradation of nitrobenzene using titaniumdioxide and concentrated solar radiation chemical effects andscaleuprdquoWater Research vol 37 no 6 pp 1223ndash1230 2003

[17] M Saif and M S A Abdel-Mottaleb ldquoTitanium dioxidenanomaterial dopedwith trivalent lanthanide ions of Tb Eu andSm preparation characterization and potential applicationsrdquoInorganica Chimica Acta vol 360 no 9 pp 2863ndash2874 2007

[18] A Alouche ldquoPreparation and characterization of Copper andor Cerium catalysts supported on Alumina or Ceriardquo JordanJournal of Mechanical and Industrial Engineering vol 2 pp 111ndash116 2008

[19] R J Tayade P K Surolia R G Kulkarni and R V JasraldquoPhotocatalytic degradation of dyes and organic contaminantsin water using nanocrystalline anatase and rutile TiO

2rdquo Science

and Technology of AdvancedMaterials vol 8 no 6 pp 455ndash4622007

[20] X-Z Shen Z-C Liu S-M Xie and J Guo ldquoDegradationof nitrobenzene using titania photocatalyst co-doped withnitrogen and cerium under visible light illuminationrdquo Journalof Hazardous Materials vol 162 no 2-3 pp 1193ndash1198 2009

[21] WWang Y Huang and S Yang ldquoPhotocatalytic degradation ofnitrobenzene wastewater with H

3PW12O40TiO2rdquo in Proceed-

ings of the International Conference on Mechanic Automationand Control Engineering (MACE rsquo10) pp 1303ndash1305 June 2010

[22] P K Surolia R J Tayade and R V Jasra ldquoPhotocatalytic degra-dation of nitrobenzene in an aqueous system by transition-metal-exchanged ETS-10 zeolitesrdquo Industrial and EngineeringChemistry Research vol 49 no 8 pp 3961ndash3966 2010

[23] W Bahnemann M Muneer and M M Haque ldquoTitaniumdioxide-mediated photocatalysed degradation of few selectedorganic pollutants in aqueous suspensionsrdquoCatalysis Today vol124 no 3-4 pp 133ndash148 2007

[24] A E Cassano and O M Alfano ldquoReaction engineering of sus-pended solid heterogeneous photocatalytic reactorsrdquo CatalysisToday vol 58 no 2 pp 167ndash197 2000

[25] A A Adesina ldquoIndustrial exploitation of photocatalysis pro-gress perspectives and prospectsrdquo Catalysis Surveys from Asiavol 8 no 4 pp 265ndash273 2004

[26] Y Ku and C B Hsieh ldquoPhotocatalytic decomposition of 24-dichlorophenol in aqueous TiO

2suspensionsrdquoWater Research

vol 26 no 11 pp 1451ndash1456 1992

Impact Factor 173028 Days Fast Track Peer ReviewAll Subject Areas of ScienceSubmit at httpwwwtswjcom

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawi Publishing Corporation httpwwwhindawicom Volume 2013

The Scientific World Journal

4 International Journal of Photoenergy

875 880 885 890 895

Inte

nsity

(au

)

Binding energy (eV)

Ce 3d

8873 eV

(a)

Inte

nsity

(au

)

Binding energy (eV)454 458 462 466 470 474

Ti 2p

4585 eV

4645 eV

(b)

Figure 2 XPS analysis of TiO2-Ce doped catalyst

(a) (b)

Figure 3 SEM analysis of TiO2(a) and TiO

2-Ce (b) doped catalyst

3000

2000

1000

00 1 2 3 4 5

TiO2-Ce

OTi

Ce Ti

OTi

Ce Ti

(keV)

Full scale counts 3320

(a)

0 1 2 3 4 5

OTi

Ti

Ti

TiO2

2500

2000

1500

1000

500

0

OTi

Ti

Ti

(keV)klm-80-Hg

(b)

Figure 4 EDX analysis of TiO2-Ce doped and TiO

2catalyst

International Journal of Photoenergy 5

Table 2 Catalyst composition using EDX analysis of TiO2 andTiO2-Ce catalyst

Element Compound TiO2 TiO2-Ce

O 1183 1965Ti 8817 7656Ce mdash 379

and quantitative information about the elemental and atomicpercentages in the TiO

2and TiO

2-Ce samples as presented

in Table 2In order to estimate the band gap distance UV-vis

spectroscopy was employed An Oriel Instruments spec-trometer with an integrating sphere was used for UV-Visspectrometry measurements to analyze the red-shifts in theabsorption regionsTheUV-Vis transmittancemeasurementswere taken and converted into absorption readings as given inFigure 5 For pure TiO

2 the band gap energy correpsonding

to 3888 nm indicates 318 eV which was found to be inaccordance with that of other researchers [20ndash22] while forTiO2-Ce the band gap energy reduced due to the shift of

absorbance further away from UV region The band gapenergy corresponding to the wavelength of 5514 nm wasdetermined to be 225 eV The results show that cerium doesimprove visible light absorbance of TiO

2due to cerium

plasmon absorption

32 Control Experiment Photocatalytic degradation studieswere performed using TiO

2-Ce and compared with undoped

TiO2 The catalyst dosage was uniformly taken to be 01 g Lminus1

for all the experiments with solution concentration to be50mg Lminus1 pH of 68 and different light intensities (150 300and 500W) From Figure 6 it could be seen that using TiO

2-

Ce and 500W light the degradation achieved was 7909whichwas higher than the other catalysts studied Addition ofCerium to TiO

2has increased the percentage of degradation

by 14 when compared to TiO2 The photolytic degradation

of nitrobenzene was performed in the absence of the catalystvarying the intensity of the visible light for comparing theperformance of cerium doped catalyst as shown in Figure 6The degradation using 150 300 and 500W was found to be23 25 and 29 respectively This was much lower than thedegradation using Cerium doped catalyst

Though the particle size of TiO2-Ce was higher than

TiO2(solgel) it showed better degradation because in photo-

catalysis doping a semiconductor changed the photocatalyticprocess by suppressing electron-hole recombination andwhen the electron formed due to excitation migrates to themetal it gets trapped withinThe organic compound diffusesto the free hole on the semiconductor surface and oxidationof nitrobenzene occurs The presence of cerium species onTiO2influences the photoreactivity by altering the electron-

hole pair recombination rate through the following equations(4)ndash(7) The reduction in band gap energy from 32 eV to

300 350 400 450 500 550 600 650 700

Abso

rban

ce (a

u)

Wavelength (nm)

Ti-CeTiO2 (solgel)

Figure 5 UV-DRIFT analysis of TiO2and TiO

2-Ce catalyst

231

6

251

8

289

4

591

5

620

1

651

4

689

8

711

6 791

4

208

4

226

6

260

5

544

1

573

6

601

3

651

9

663

2 728

9

0102030405060708090

Degradation ()TOC removal ()

Phot

olys

is (150

W)

Phot

olys

is (300

W)

Phot

olys

is (500

W)

TiO

2(s

olge

l)(150

W)

TiO

2(s

olge

l)(300

W)

TiO

2(s

olge

l)(500

W)

TiO

2-C

e (150

W)

TiO

2-C

e (300

W)

TiO

2-C

e (500

W)

Figure 6 Degradation of NB for different catalysts at differentintensities (Conc 50mg Lminus1 pH 68 and catalyst dosage 01 g Lminus1)

225 eV also contributed to this increase in degradationConsider

Ce3+ +O2997888rarr∙Ominus2 + Ce4+ (4)

Ce4+ + eminus 997888rarr Ce3+ (5)

Ce3+ + TiO2+ ℎ] 997888rarr eminus + h+ (6)

Ce2O3+ ℎ] 997888rarr eminus + h+ (7)

The present study revealed that the cerium doped TiO2in

sol-sol method could be effectively used as compared to othercatalysts as discussed in Table 3 Better shift of the catalysttowards visible region has resulted in 100 degradation ata pH of 9 and catalyst dosage of 01 gLminus1 (as summarized inSection 335)

6 International Journal of Photoenergy

Table 3 Comparison of the performance of the present work with other published works

Catalyst Properties Light source degradation Reference

Ce doped TiO2

Particle size 108 nmSurface area 896m2gminus1

Band gap 368 nmVisible 5 for 50mgLminus1 of

NB solutionAlouche (2008)

[18]

H3PW12O40-TiO2 Visible 941 of 20mgLminus1 ofNB solution in 65 hrs

Tayade et al(2007) [19]

Fe-ETS-10 Surface area 191m2gminus1Band gap 313 eV UV 43 of 50mgLminus1 of

NB solution in 4 hrsShen et al(2009) [20]

NanocrystallineTiO2

Particle size 12 nmSurface area 166m2gminus1

Band gap 328 eVVisible 96 of 50mgLminus1 of

NB solution in 8 hrsTayade et al(2006) [6]

Silver metalexchanged ETS-10Zeolite

Surface area 205m2gminus1Band gap 316 eV UV light (267 nm) 57 50mgLminus1 of NB

solution in 4 hrsShen et al(2009) [20]

N-Ce doped TiO2

Particle size 108 nmSurface area 152m2gminus1

Band gap 219 eVVisible (300W xenon lamp) 53 50mgLminus1 of NB

solution in 4 hrsAlouche (2008)

[18]

The TOC removal was studied for different intervalsof time The photomineralization of the compounds weremeasured using Total Organic Carbon analyzer (ShimadzuTOC 5000A) The extent of TOC removal was comparedwith the undoped and Cerium doped TiO

2catalystThe TOC

removal was maximum using Cerium doped catalyst at anintensity of 500W

33 Optimization of Operational Parameters

331 Effect of Solution Concentration The most importantoperational parameter to be studied is the influence of initialconcentration of the solution NB photocatalytic degradationstudies were carried out using 25ndash200mg Lminus1 initial concen-tration of NB and 01 g Lminus1 of catalyst loading The plot ofdegradation for different solution concentration was madeand from Figure 7 it could be inferred that as concentrationincreased percentage degradation decreased This may bedue to the fact that with the increase in initial concentrationof NB while the irradiation period and catalyst dose arekept constant more NB molecules are present on the surfaceof TiO

2 Thus an increase in the number of substrate ions

accommodating in interlayer spacing inhibits the action ofthe catalyst which thereby decreases the number of reactive∙OH and O∙minus

2free radicals attacking the NB molecules and

hence lowers the photodegradation efficiency [23]

332 Effect of Light Intensity The influence of light intensityon the degradation efficiency has been examined at constantNitrobenzene concentration (50mg Lminus1) at pH (65) andcatalyst loading (01 g Lminus1) It is evident that the degradationrate increases with increase in the light intensity as shownin Figure 6 The photons required for the electron transferwere generated by UV irradiation which results in electrontransfer fromvalence band to conduction bandof the catalystThe degradation increases when more radiations fall on

0

10

20

30

40

50

60

70

80

90

050 100 150 200 250 300 350 400

Deg

rada

tion

()

Time (min)

25mgLminus1

75mgLminus1

150mgLminus1

50mgLminus1

100mgLminus1

200mgLminus1

Figure 7 Effect of solution concentration on degradation (lightintensity 500W pH 68 and catalyst dosage 01 g Lminus1)

the catalyst surface and hence more hydroxyl radicals areproduced [24]

333 Effect of Catalyst Dosage Photocatalyst dosage addedto the reaction vessel is a major parameter affecting thephotocatalytic degradation efficiency The aqueous solutionof 50mg Lminus1 of solution was degraded using different catalystdosages (0025 005 01 015 and 02 g Lminus1) From Figure 8it can be seen that maximum degradation was achieved forthe catalyst dosage of 01 g Lminus1 It could also be inferred thatfurther increase in catalyst dosage did not yield an increasein degradation percentage

International Journal of Photoenergy 7

68

70

72

74

76

78

80

0 005 01 015 02 025

Deg

rada

tion

()

Catalyst dosage (gLminus1)

Figure 8 Effect of catalyst dosage on degradation (Conc50mg Lminus1 pH 68 and intensity 500W)

The increase in degradation percentage for 0025 to01 g Lminus1 may be due to an increase in the amount of activesites on the surface of the photocatalyst particlesThe numberof NB molecules adsorbed as well as the number of photonsabsorbed increase with the increase in catalyst concentrationthereby enhancing the rate of degradation Addition ofcatalyst beyond 01 g Lminus1 leads to decrease in the degradationAggregation of TiO

2particles occurs at higher dosage causing

decrease in the number of surface active sites and also there isan increase in the opacity of the solution and light scatteringof TiO

2particles at high dosage through the solution [25]

334 Effect of pH of the Solution pH of the solution greatlyinfluences the degradation rate It tends to change the surfaceproperty of the catalyst The effect of change in initial pH(2 4 65 8 9 10 and 11) of 50mg Lminus1 of the nitrobenzenesolution was studied by adding 01 g Lminus1 of catalyst The plotof degradation against pH (Figure 9) showed that as pHincreased the degradation increased A maximum of 100degradation was achieved at pH 9The degradation was lowerin lower acidic and higher alkaline pH

pH of the catalyst dispersions majorly affects the surfaceproperties on the particles agglomerate size formed andthe conductance and valence bands positions [26] Thenitrobenzene solution was degraded by hydroxyl attack anddirect oxidation at the holes and reduction at the conductionband In alkaline pH the surface of TiO

2-Ce acquires a

negative charge leading to greater adsorption and henceincreasing the degradation rate in the alkaline media

335 Kinetic Modelling Using Langmuir Hinshelwood ModelThe degradation percentage was calculated and for hetero-geneous catalyst the Langmuir Hinshelwood model wasused to calculate the apparent rate constant The LangmuirHinshelwoodmodel derived based on themonolayer activityassumption was used to estimate the kinetic parameters in

72

74

76

78

80

82

84

86

0 2 4 6 8 10 12

Deg

rada

tion

()

Solution pH

Figure 9 Effect of solution pH on degradation (Conc 50mg Lminus1catalyst dosage 01 g Lminus1 and intensity 500W)

0

02

04

06

08

1

12

14

16

18

2

0 50 100 150 200 250 300 350 400Time (min)

25mgLminus1

75mgLminus1150mgLminus150mgLminus1100mgLminus1

200mgLminus1

ln(C

0C

)

Figure 10 Langmuir Hinshelwood plot (pH 68 catalyst dosage01 g Lminus1 and light intensity 500W)

terms of reaction rate constant (119896119903) and Langmuir Hinshel-

wood adsorption constant (119870LH) which is as given in

119903 =119896119903119870LH119862

1 + 119870LH1198620= 119896app119862 (8)

where is rate of disappearance of organic substratemg Lminus1minminus1 and 119862 is concentration of organic substratemg Lminus1

119896app =119896119903119870LH

1 + 119870LH1198620 (9)

Linearization of (8) yields an equation from which a plotof ln (119862

0119862) against time will result in a linear relation-

ship resulting in zero intercept and apparent rate constant(119896app) derived from the slope of the line Figure 10 is the

8 International Journal of Photoenergy

0

01

02

03

04

05

06

0 0001 0002 0003 0004 0005 0006

times10minus2

kap

p(m

inminus1) (

theo

)

kapp (minminus1) (exp)

Figure 11 Comparison between the experimental and theoreticalvalues of apparent rate constant

representation of the plot from which the apparent rateconstant was determined using slope of the line Similarlyfor all the conditions of pH (2ndash11) concentration (25ndash200mg Lminus1) catalyst dosage (0025ndash02 g Lminus1) and intensityof visible light (150ndash500W) the plot of ln (119862

0119862) against

time was evaluated The apparent rate constant was foundto increase with light intensity and decrease with solutionconcentrationThemaximum degradation could be achievedat the following parameter condition pH 9 dosage 01 g Lminus1solution concentration 25mg Lminus1 and light intensity 500WThe nonlinear fit between the apparent rate constant and theoperational parameters was determined and were found thatthe experimental values when compared with the theoreticalvalues as in Figure 11 the theoretical values had less than 3error and hence the following equation (10) could be chosenfor approximating the experimental conditions Equation(10) could be used for a condition of pH 2 to 9 dosageof 005 to 01 g Lminus1 light intensity of 150 300 or 500Wand concentration of solution from 25 to 200mg Lminus1 Thenonlinear equation was

119896app (theoretical)

= 0000229 lowast Intensity0584 lowast Concentrationminus0230

lowast Dosage0425 lowast pH0336(10)

4 Conclusion

The undoped and cerium doped titania photocatalyst wasprepared through the sol-gel route The cerium doped pho-tocatalyst could absorb the visible light and showed highphotoactivity in the visible region because of the band gapnarrowing Cerium atoms existed in the state of Ce

2O3

and were dispersed on the surface of titania suppressingthe recombination of electron-hole pairs and increasing thephotoactivity as confirmed using XPS and DRIFT analysis

The average crystal size and the surface area were deter-mined and compared between two types of catalysts Theoperational parameters were optimized and the followingcondition was suggested to obtain maximum degradationpH 9 dosage 01 g Lminus1 solution concentration 25mg Lminus1and light intensity 500W The kinetic study revealed thatthe degradation followed Langmuir Hinshelwood modelThe apparent rate constant was determined and evaluatedtheoretically using the nonlinear fit which depends on theoperational parameters Based on the previously mentionedexperiments and characterization it could be concluded thatCeriumdoped TiO

2catalyst prepared by solgelmethod could

be efficiently used for degradation of Nitrobenzene usingvisible light

References

[1] S C Moon H Mametsuka S Tabata and E Suzuki ldquoPhoto-catalytic production of hydrogen from water using TiO

2and

BTiO2rdquo Catalysis Today vol 58 no 2 pp 125ndash132 2000

[2] C Lettmann K Hildenbrand H Kisch W Macyk and WF Maier ldquoVisible light photodegradation of 4-chlorophenolwith a coke-containing titaniumdioxide photocatalystrdquoAppliedCatalysis B vol 32 no 4 pp 215ndash227 2001

[3] 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

[4] C-S Wu and C Chen ldquoA visible-light response vanadium-doped titania nanocatalyst by sol-gel methodrdquo Journal of Photo-chemistry and Photobiology A vol 163 no 3 pp 509ndash515 2004

[5] T Umebayashi T Yamaki S Tanaka and K Asai ldquoVisiblelight-induced degradation ofmethylene blue on S-doped TiO

2rdquo

Chemistry Letters vol 32 no 4 pp 330ndash331 2003[6] R J Tayade R G Kulkarni and R V Jasra ldquoPhotocatalytic

degradation of aqueous nitrobenzene by nanocrystalline TiO2rdquo

Industrial and Engineering Chemistry Research vol 45 no 3 pp922ndash927 2006

[7] M H Priya and G Madras ldquoPhotocatalytic degradation ofnitrobenzenes with combustion synthesized nano-TiO

2rdquo Jour-

nal of Photochemistry and Photobiology A vol 178 no 1 pp 1ndash72006

[8] S Ikeda N Sugiyama B Pal et al ldquoPhotocatalytic activityof transition-metal-loaded titanium(IV) oxide powders sus-pended in aqueous solutions correlation with electron-holerecombination kineticsrdquo Physical Chemistry Chemical Physicsvol 3 no 2 pp 267ndash273 2001

[9] A Fuerte M D Hernandez-Alonso A J Maira et al ldquoVisiblelight-activated nanosized doped-TiO

2photocatalystsrdquo Chemi-

cal Communications no 24 pp 2718ndash2719 2001[10] W Choi A Termin and M R Hoffmann ldquoThe role of

metal ion dopants in quantum-sized TiO2 correlation between

photoreactivity and charge carrier recombination dynamicsrdquoJournal of Physical Chemistry vol 98 no 51 pp 13669ndash136791994

[11] B M Reddy P M Sreekanth Y Yamada Q Xu and TKobayashi ldquoSurface characterization of sulfate molybdate andtungstate promoted TiO

2-ZrO2solid acid catalysts by XPS and

other techniquesrdquoApplied Catalysis A vol 228 no 1-2 pp 269ndash278 2002

International Journal of Photoenergy 9

[12] VMOrera R IMerino and F Pena ldquoCe3+harrCe4+ conversionin ceria-doped zirconia single crystals induced by oxido-reduction treatmentsrdquo Solid State Ionics vol 72 no 2 pp 224ndash231 1994

[13] W M Yen M Raukas S A Basun W Van Schaik and UHappek ldquoOptical and photoconductive properties of cerium-doped crystalline solidsrdquo Journal of Luminescence vol 69 no5-6 pp 287ndash294 1996

[14] S W Chen J M Lee K T Lu et al ldquoBand-gap narrowingof TiO

2doped with Ce probed with x-ray absorption spec-

troscopyrdquo Applied Physics Letters vol 97 no 1 Article ID012104 2010

[15] H Liu X Z Li Y J Leng andW Z Li ldquoAn alternative approachto ascertain the rate-determining steps of TiO

2photoelectro-

catalytic reaction by electrochemical impedance spectroscopyrdquoJournal of Physical Chemistry B vol 107 no 34 pp 8988ndash89962003

[16] D S Bhatkhande V G Pangarkar and A A C M BeenackersldquoPhotocatalytic degradation of nitrobenzene using titaniumdioxide and concentrated solar radiation chemical effects andscaleuprdquoWater Research vol 37 no 6 pp 1223ndash1230 2003

[17] M Saif and M S A Abdel-Mottaleb ldquoTitanium dioxidenanomaterial dopedwith trivalent lanthanide ions of Tb Eu andSm preparation characterization and potential applicationsrdquoInorganica Chimica Acta vol 360 no 9 pp 2863ndash2874 2007

[18] A Alouche ldquoPreparation and characterization of Copper andor Cerium catalysts supported on Alumina or Ceriardquo JordanJournal of Mechanical and Industrial Engineering vol 2 pp 111ndash116 2008

[19] R J Tayade P K Surolia R G Kulkarni and R V JasraldquoPhotocatalytic degradation of dyes and organic contaminantsin water using nanocrystalline anatase and rutile TiO

2rdquo Science

and Technology of AdvancedMaterials vol 8 no 6 pp 455ndash4622007

[20] X-Z Shen Z-C Liu S-M Xie and J Guo ldquoDegradationof nitrobenzene using titania photocatalyst co-doped withnitrogen and cerium under visible light illuminationrdquo Journalof Hazardous Materials vol 162 no 2-3 pp 1193ndash1198 2009

[21] WWang Y Huang and S Yang ldquoPhotocatalytic degradation ofnitrobenzene wastewater with H

3PW12O40TiO2rdquo in Proceed-

ings of the International Conference on Mechanic Automationand Control Engineering (MACE rsquo10) pp 1303ndash1305 June 2010

[22] P K Surolia R J Tayade and R V Jasra ldquoPhotocatalytic degra-dation of nitrobenzene in an aqueous system by transition-metal-exchanged ETS-10 zeolitesrdquo Industrial and EngineeringChemistry Research vol 49 no 8 pp 3961ndash3966 2010

[23] W Bahnemann M Muneer and M M Haque ldquoTitaniumdioxide-mediated photocatalysed degradation of few selectedorganic pollutants in aqueous suspensionsrdquoCatalysis Today vol124 no 3-4 pp 133ndash148 2007

[24] A E Cassano and O M Alfano ldquoReaction engineering of sus-pended solid heterogeneous photocatalytic reactorsrdquo CatalysisToday vol 58 no 2 pp 167ndash197 2000

[25] A A Adesina ldquoIndustrial exploitation of photocatalysis pro-gress perspectives and prospectsrdquo Catalysis Surveys from Asiavol 8 no 4 pp 265ndash273 2004

[26] Y Ku and C B Hsieh ldquoPhotocatalytic decomposition of 24-dichlorophenol in aqueous TiO

2suspensionsrdquoWater Research

vol 26 no 11 pp 1451ndash1456 1992

Impact Factor 173028 Days Fast Track Peer ReviewAll Subject Areas of ScienceSubmit at httpwwwtswjcom

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawi Publishing Corporation httpwwwhindawicom Volume 2013

The Scientific World Journal

International Journal of Photoenergy 5

Table 2 Catalyst composition using EDX analysis of TiO2 andTiO2-Ce catalyst

Element Compound TiO2 TiO2-Ce

O 1183 1965Ti 8817 7656Ce mdash 379

and quantitative information about the elemental and atomicpercentages in the TiO

2and TiO

2-Ce samples as presented

in Table 2In order to estimate the band gap distance UV-vis

spectroscopy was employed An Oriel Instruments spec-trometer with an integrating sphere was used for UV-Visspectrometry measurements to analyze the red-shifts in theabsorption regionsTheUV-Vis transmittancemeasurementswere taken and converted into absorption readings as given inFigure 5 For pure TiO

2 the band gap energy correpsonding

to 3888 nm indicates 318 eV which was found to be inaccordance with that of other researchers [20ndash22] while forTiO2-Ce the band gap energy reduced due to the shift of

absorbance further away from UV region The band gapenergy corresponding to the wavelength of 5514 nm wasdetermined to be 225 eV The results show that cerium doesimprove visible light absorbance of TiO

2due to cerium

plasmon absorption

32 Control Experiment Photocatalytic degradation studieswere performed using TiO

2-Ce and compared with undoped

TiO2 The catalyst dosage was uniformly taken to be 01 g Lminus1

for all the experiments with solution concentration to be50mg Lminus1 pH of 68 and different light intensities (150 300and 500W) From Figure 6 it could be seen that using TiO

2-

Ce and 500W light the degradation achieved was 7909whichwas higher than the other catalysts studied Addition ofCerium to TiO

2has increased the percentage of degradation

by 14 when compared to TiO2 The photolytic degradation

of nitrobenzene was performed in the absence of the catalystvarying the intensity of the visible light for comparing theperformance of cerium doped catalyst as shown in Figure 6The degradation using 150 300 and 500W was found to be23 25 and 29 respectively This was much lower than thedegradation using Cerium doped catalyst

Though the particle size of TiO2-Ce was higher than

TiO2(solgel) it showed better degradation because in photo-

catalysis doping a semiconductor changed the photocatalyticprocess by suppressing electron-hole recombination andwhen the electron formed due to excitation migrates to themetal it gets trapped withinThe organic compound diffusesto the free hole on the semiconductor surface and oxidationof nitrobenzene occurs The presence of cerium species onTiO2influences the photoreactivity by altering the electron-

hole pair recombination rate through the following equations(4)ndash(7) The reduction in band gap energy from 32 eV to

300 350 400 450 500 550 600 650 700

Abso

rban

ce (a

u)

Wavelength (nm)

Ti-CeTiO2 (solgel)

Figure 5 UV-DRIFT analysis of TiO2and TiO

2-Ce catalyst

231

6

251

8

289

4

591

5

620

1

651

4

689

8

711

6 791

4

208

4

226

6

260

5

544

1

573

6

601

3

651

9

663

2 728

9

0102030405060708090

Degradation ()TOC removal ()

Phot

olys

is (150

W)

Phot

olys

is (300

W)

Phot

olys

is (500

W)

TiO

2(s

olge

l)(150

W)

TiO

2(s

olge

l)(300

W)

TiO

2(s

olge

l)(500

W)

TiO

2-C

e (150

W)

TiO

2-C

e (300

W)

TiO

2-C

e (500

W)

Figure 6 Degradation of NB for different catalysts at differentintensities (Conc 50mg Lminus1 pH 68 and catalyst dosage 01 g Lminus1)

225 eV also contributed to this increase in degradationConsider

Ce3+ +O2997888rarr∙Ominus2 + Ce4+ (4)

Ce4+ + eminus 997888rarr Ce3+ (5)

Ce3+ + TiO2+ ℎ] 997888rarr eminus + h+ (6)

Ce2O3+ ℎ] 997888rarr eminus + h+ (7)

The present study revealed that the cerium doped TiO2in

sol-sol method could be effectively used as compared to othercatalysts as discussed in Table 3 Better shift of the catalysttowards visible region has resulted in 100 degradation ata pH of 9 and catalyst dosage of 01 gLminus1 (as summarized inSection 335)

6 International Journal of Photoenergy

Table 3 Comparison of the performance of the present work with other published works

Catalyst Properties Light source degradation Reference

Ce doped TiO2

Particle size 108 nmSurface area 896m2gminus1

Band gap 368 nmVisible 5 for 50mgLminus1 of

NB solutionAlouche (2008)

[18]

H3PW12O40-TiO2 Visible 941 of 20mgLminus1 ofNB solution in 65 hrs

Tayade et al(2007) [19]

Fe-ETS-10 Surface area 191m2gminus1Band gap 313 eV UV 43 of 50mgLminus1 of

NB solution in 4 hrsShen et al(2009) [20]

NanocrystallineTiO2

Particle size 12 nmSurface area 166m2gminus1

Band gap 328 eVVisible 96 of 50mgLminus1 of

NB solution in 8 hrsTayade et al(2006) [6]

Silver metalexchanged ETS-10Zeolite

Surface area 205m2gminus1Band gap 316 eV UV light (267 nm) 57 50mgLminus1 of NB

solution in 4 hrsShen et al(2009) [20]

N-Ce doped TiO2

Particle size 108 nmSurface area 152m2gminus1

Band gap 219 eVVisible (300W xenon lamp) 53 50mgLminus1 of NB

solution in 4 hrsAlouche (2008)

[18]

The TOC removal was studied for different intervalsof time The photomineralization of the compounds weremeasured using Total Organic Carbon analyzer (ShimadzuTOC 5000A) The extent of TOC removal was comparedwith the undoped and Cerium doped TiO

2catalystThe TOC

removal was maximum using Cerium doped catalyst at anintensity of 500W

33 Optimization of Operational Parameters

331 Effect of Solution Concentration The most importantoperational parameter to be studied is the influence of initialconcentration of the solution NB photocatalytic degradationstudies were carried out using 25ndash200mg Lminus1 initial concen-tration of NB and 01 g Lminus1 of catalyst loading The plot ofdegradation for different solution concentration was madeand from Figure 7 it could be inferred that as concentrationincreased percentage degradation decreased This may bedue to the fact that with the increase in initial concentrationof NB while the irradiation period and catalyst dose arekept constant more NB molecules are present on the surfaceof TiO

2 Thus an increase in the number of substrate ions

accommodating in interlayer spacing inhibits the action ofthe catalyst which thereby decreases the number of reactive∙OH and O∙minus

2free radicals attacking the NB molecules and

hence lowers the photodegradation efficiency [23]

332 Effect of Light Intensity The influence of light intensityon the degradation efficiency has been examined at constantNitrobenzene concentration (50mg Lminus1) at pH (65) andcatalyst loading (01 g Lminus1) It is evident that the degradationrate increases with increase in the light intensity as shownin Figure 6 The photons required for the electron transferwere generated by UV irradiation which results in electrontransfer fromvalence band to conduction bandof the catalystThe degradation increases when more radiations fall on

0

10

20

30

40

50

60

70

80

90

050 100 150 200 250 300 350 400

Deg

rada

tion

()

Time (min)

25mgLminus1

75mgLminus1

150mgLminus1

50mgLminus1

100mgLminus1

200mgLminus1

Figure 7 Effect of solution concentration on degradation (lightintensity 500W pH 68 and catalyst dosage 01 g Lminus1)

the catalyst surface and hence more hydroxyl radicals areproduced [24]

333 Effect of Catalyst Dosage Photocatalyst dosage addedto the reaction vessel is a major parameter affecting thephotocatalytic degradation efficiency The aqueous solutionof 50mg Lminus1 of solution was degraded using different catalystdosages (0025 005 01 015 and 02 g Lminus1) From Figure 8it can be seen that maximum degradation was achieved forthe catalyst dosage of 01 g Lminus1 It could also be inferred thatfurther increase in catalyst dosage did not yield an increasein degradation percentage

International Journal of Photoenergy 7

68

70

72

74

76

78

80

0 005 01 015 02 025

Deg

rada

tion

()

Catalyst dosage (gLminus1)

Figure 8 Effect of catalyst dosage on degradation (Conc50mg Lminus1 pH 68 and intensity 500W)

The increase in degradation percentage for 0025 to01 g Lminus1 may be due to an increase in the amount of activesites on the surface of the photocatalyst particlesThe numberof NB molecules adsorbed as well as the number of photonsabsorbed increase with the increase in catalyst concentrationthereby enhancing the rate of degradation Addition ofcatalyst beyond 01 g Lminus1 leads to decrease in the degradationAggregation of TiO

2particles occurs at higher dosage causing

decrease in the number of surface active sites and also there isan increase in the opacity of the solution and light scatteringof TiO

2particles at high dosage through the solution [25]

334 Effect of pH of the Solution pH of the solution greatlyinfluences the degradation rate It tends to change the surfaceproperty of the catalyst The effect of change in initial pH(2 4 65 8 9 10 and 11) of 50mg Lminus1 of the nitrobenzenesolution was studied by adding 01 g Lminus1 of catalyst The plotof degradation against pH (Figure 9) showed that as pHincreased the degradation increased A maximum of 100degradation was achieved at pH 9The degradation was lowerin lower acidic and higher alkaline pH

pH of the catalyst dispersions majorly affects the surfaceproperties on the particles agglomerate size formed andthe conductance and valence bands positions [26] Thenitrobenzene solution was degraded by hydroxyl attack anddirect oxidation at the holes and reduction at the conductionband In alkaline pH the surface of TiO

2-Ce acquires a

negative charge leading to greater adsorption and henceincreasing the degradation rate in the alkaline media

335 Kinetic Modelling Using Langmuir Hinshelwood ModelThe degradation percentage was calculated and for hetero-geneous catalyst the Langmuir Hinshelwood model wasused to calculate the apparent rate constant The LangmuirHinshelwoodmodel derived based on themonolayer activityassumption was used to estimate the kinetic parameters in

72

74

76

78

80

82

84

86

0 2 4 6 8 10 12

Deg

rada

tion

()

Solution pH

Figure 9 Effect of solution pH on degradation (Conc 50mg Lminus1catalyst dosage 01 g Lminus1 and intensity 500W)

0

02

04

06

08

1

12

14

16

18

2

0 50 100 150 200 250 300 350 400Time (min)

25mgLminus1

75mgLminus1150mgLminus150mgLminus1100mgLminus1

200mgLminus1

ln(C

0C

)

Figure 10 Langmuir Hinshelwood plot (pH 68 catalyst dosage01 g Lminus1 and light intensity 500W)

terms of reaction rate constant (119896119903) and Langmuir Hinshel-

wood adsorption constant (119870LH) which is as given in

119903 =119896119903119870LH119862

1 + 119870LH1198620= 119896app119862 (8)

where is rate of disappearance of organic substratemg Lminus1minminus1 and 119862 is concentration of organic substratemg Lminus1

119896app =119896119903119870LH

1 + 119870LH1198620 (9)

Linearization of (8) yields an equation from which a plotof ln (119862

0119862) against time will result in a linear relation-

ship resulting in zero intercept and apparent rate constant(119896app) derived from the slope of the line Figure 10 is the

8 International Journal of Photoenergy

0

01

02

03

04

05

06

0 0001 0002 0003 0004 0005 0006

times10minus2

kap

p(m

inminus1) (

theo

)

kapp (minminus1) (exp)

Figure 11 Comparison between the experimental and theoreticalvalues of apparent rate constant

representation of the plot from which the apparent rateconstant was determined using slope of the line Similarlyfor all the conditions of pH (2ndash11) concentration (25ndash200mg Lminus1) catalyst dosage (0025ndash02 g Lminus1) and intensityof visible light (150ndash500W) the plot of ln (119862

0119862) against

time was evaluated The apparent rate constant was foundto increase with light intensity and decrease with solutionconcentrationThemaximum degradation could be achievedat the following parameter condition pH 9 dosage 01 g Lminus1solution concentration 25mg Lminus1 and light intensity 500WThe nonlinear fit between the apparent rate constant and theoperational parameters was determined and were found thatthe experimental values when compared with the theoreticalvalues as in Figure 11 the theoretical values had less than 3error and hence the following equation (10) could be chosenfor approximating the experimental conditions Equation(10) could be used for a condition of pH 2 to 9 dosageof 005 to 01 g Lminus1 light intensity of 150 300 or 500Wand concentration of solution from 25 to 200mg Lminus1 Thenonlinear equation was

119896app (theoretical)

= 0000229 lowast Intensity0584 lowast Concentrationminus0230

lowast Dosage0425 lowast pH0336(10)

4 Conclusion

The undoped and cerium doped titania photocatalyst wasprepared through the sol-gel route The cerium doped pho-tocatalyst could absorb the visible light and showed highphotoactivity in the visible region because of the band gapnarrowing Cerium atoms existed in the state of Ce

2O3

and were dispersed on the surface of titania suppressingthe recombination of electron-hole pairs and increasing thephotoactivity as confirmed using XPS and DRIFT analysis

The average crystal size and the surface area were deter-mined and compared between two types of catalysts Theoperational parameters were optimized and the followingcondition was suggested to obtain maximum degradationpH 9 dosage 01 g Lminus1 solution concentration 25mg Lminus1and light intensity 500W The kinetic study revealed thatthe degradation followed Langmuir Hinshelwood modelThe apparent rate constant was determined and evaluatedtheoretically using the nonlinear fit which depends on theoperational parameters Based on the previously mentionedexperiments and characterization it could be concluded thatCeriumdoped TiO

2catalyst prepared by solgelmethod could

be efficiently used for degradation of Nitrobenzene usingvisible light

References

[1] S C Moon H Mametsuka S Tabata and E Suzuki ldquoPhoto-catalytic production of hydrogen from water using TiO

2and

BTiO2rdquo Catalysis Today vol 58 no 2 pp 125ndash132 2000

[2] C Lettmann K Hildenbrand H Kisch W Macyk and WF Maier ldquoVisible light photodegradation of 4-chlorophenolwith a coke-containing titaniumdioxide photocatalystrdquoAppliedCatalysis B vol 32 no 4 pp 215ndash227 2001

[3] 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

[4] C-S Wu and C Chen ldquoA visible-light response vanadium-doped titania nanocatalyst by sol-gel methodrdquo Journal of Photo-chemistry and Photobiology A vol 163 no 3 pp 509ndash515 2004

[5] T Umebayashi T Yamaki S Tanaka and K Asai ldquoVisiblelight-induced degradation ofmethylene blue on S-doped TiO

2rdquo

Chemistry Letters vol 32 no 4 pp 330ndash331 2003[6] R J Tayade R G Kulkarni and R V Jasra ldquoPhotocatalytic

degradation of aqueous nitrobenzene by nanocrystalline TiO2rdquo

Industrial and Engineering Chemistry Research vol 45 no 3 pp922ndash927 2006

[7] M H Priya and G Madras ldquoPhotocatalytic degradation ofnitrobenzenes with combustion synthesized nano-TiO

2rdquo Jour-

nal of Photochemistry and Photobiology A vol 178 no 1 pp 1ndash72006

[8] S Ikeda N Sugiyama B Pal et al ldquoPhotocatalytic activityof transition-metal-loaded titanium(IV) oxide powders sus-pended in aqueous solutions correlation with electron-holerecombination kineticsrdquo Physical Chemistry Chemical Physicsvol 3 no 2 pp 267ndash273 2001

[9] A Fuerte M D Hernandez-Alonso A J Maira et al ldquoVisiblelight-activated nanosized doped-TiO

2photocatalystsrdquo Chemi-

cal Communications no 24 pp 2718ndash2719 2001[10] W Choi A Termin and M R Hoffmann ldquoThe role of

metal ion dopants in quantum-sized TiO2 correlation between

photoreactivity and charge carrier recombination dynamicsrdquoJournal of Physical Chemistry vol 98 no 51 pp 13669ndash136791994

[11] B M Reddy P M Sreekanth Y Yamada Q Xu and TKobayashi ldquoSurface characterization of sulfate molybdate andtungstate promoted TiO

2-ZrO2solid acid catalysts by XPS and

other techniquesrdquoApplied Catalysis A vol 228 no 1-2 pp 269ndash278 2002

International Journal of Photoenergy 9

[12] VMOrera R IMerino and F Pena ldquoCe3+harrCe4+ conversionin ceria-doped zirconia single crystals induced by oxido-reduction treatmentsrdquo Solid State Ionics vol 72 no 2 pp 224ndash231 1994

[13] W M Yen M Raukas S A Basun W Van Schaik and UHappek ldquoOptical and photoconductive properties of cerium-doped crystalline solidsrdquo Journal of Luminescence vol 69 no5-6 pp 287ndash294 1996

[14] S W Chen J M Lee K T Lu et al ldquoBand-gap narrowingof TiO

2doped with Ce probed with x-ray absorption spec-

troscopyrdquo Applied Physics Letters vol 97 no 1 Article ID012104 2010

[15] H Liu X Z Li Y J Leng andW Z Li ldquoAn alternative approachto ascertain the rate-determining steps of TiO

2photoelectro-

catalytic reaction by electrochemical impedance spectroscopyrdquoJournal of Physical Chemistry B vol 107 no 34 pp 8988ndash89962003

[16] D S Bhatkhande V G Pangarkar and A A C M BeenackersldquoPhotocatalytic degradation of nitrobenzene using titaniumdioxide and concentrated solar radiation chemical effects andscaleuprdquoWater Research vol 37 no 6 pp 1223ndash1230 2003

[17] M Saif and M S A Abdel-Mottaleb ldquoTitanium dioxidenanomaterial dopedwith trivalent lanthanide ions of Tb Eu andSm preparation characterization and potential applicationsrdquoInorganica Chimica Acta vol 360 no 9 pp 2863ndash2874 2007

[18] A Alouche ldquoPreparation and characterization of Copper andor Cerium catalysts supported on Alumina or Ceriardquo JordanJournal of Mechanical and Industrial Engineering vol 2 pp 111ndash116 2008

[19] R J Tayade P K Surolia R G Kulkarni and R V JasraldquoPhotocatalytic degradation of dyes and organic contaminantsin water using nanocrystalline anatase and rutile TiO

2rdquo Science

and Technology of AdvancedMaterials vol 8 no 6 pp 455ndash4622007

[20] X-Z Shen Z-C Liu S-M Xie and J Guo ldquoDegradationof nitrobenzene using titania photocatalyst co-doped withnitrogen and cerium under visible light illuminationrdquo Journalof Hazardous Materials vol 162 no 2-3 pp 1193ndash1198 2009

[21] WWang Y Huang and S Yang ldquoPhotocatalytic degradation ofnitrobenzene wastewater with H

3PW12O40TiO2rdquo in Proceed-

ings of the International Conference on Mechanic Automationand Control Engineering (MACE rsquo10) pp 1303ndash1305 June 2010

[22] P K Surolia R J Tayade and R V Jasra ldquoPhotocatalytic degra-dation of nitrobenzene in an aqueous system by transition-metal-exchanged ETS-10 zeolitesrdquo Industrial and EngineeringChemistry Research vol 49 no 8 pp 3961ndash3966 2010

[23] W Bahnemann M Muneer and M M Haque ldquoTitaniumdioxide-mediated photocatalysed degradation of few selectedorganic pollutants in aqueous suspensionsrdquoCatalysis Today vol124 no 3-4 pp 133ndash148 2007

[24] A E Cassano and O M Alfano ldquoReaction engineering of sus-pended solid heterogeneous photocatalytic reactorsrdquo CatalysisToday vol 58 no 2 pp 167ndash197 2000

[25] A A Adesina ldquoIndustrial exploitation of photocatalysis pro-gress perspectives and prospectsrdquo Catalysis Surveys from Asiavol 8 no 4 pp 265ndash273 2004

[26] Y Ku and C B Hsieh ldquoPhotocatalytic decomposition of 24-dichlorophenol in aqueous TiO

2suspensionsrdquoWater Research

vol 26 no 11 pp 1451ndash1456 1992

Impact Factor 173028 Days Fast Track Peer ReviewAll Subject Areas of ScienceSubmit at httpwwwtswjcom

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawi Publishing Corporation httpwwwhindawicom Volume 2013

The Scientific World Journal

6 International Journal of Photoenergy

Table 3 Comparison of the performance of the present work with other published works

Catalyst Properties Light source degradation Reference

Ce doped TiO2

Particle size 108 nmSurface area 896m2gminus1

Band gap 368 nmVisible 5 for 50mgLminus1 of

NB solutionAlouche (2008)

[18]

H3PW12O40-TiO2 Visible 941 of 20mgLminus1 ofNB solution in 65 hrs

Tayade et al(2007) [19]

Fe-ETS-10 Surface area 191m2gminus1Band gap 313 eV UV 43 of 50mgLminus1 of

NB solution in 4 hrsShen et al(2009) [20]

NanocrystallineTiO2

Particle size 12 nmSurface area 166m2gminus1

Band gap 328 eVVisible 96 of 50mgLminus1 of

NB solution in 8 hrsTayade et al(2006) [6]

Silver metalexchanged ETS-10Zeolite

Surface area 205m2gminus1Band gap 316 eV UV light (267 nm) 57 50mgLminus1 of NB

solution in 4 hrsShen et al(2009) [20]

N-Ce doped TiO2

Particle size 108 nmSurface area 152m2gminus1

Band gap 219 eVVisible (300W xenon lamp) 53 50mgLminus1 of NB

solution in 4 hrsAlouche (2008)

[18]

The TOC removal was studied for different intervalsof time The photomineralization of the compounds weremeasured using Total Organic Carbon analyzer (ShimadzuTOC 5000A) The extent of TOC removal was comparedwith the undoped and Cerium doped TiO

2catalystThe TOC

removal was maximum using Cerium doped catalyst at anintensity of 500W

33 Optimization of Operational Parameters

331 Effect of Solution Concentration The most importantoperational parameter to be studied is the influence of initialconcentration of the solution NB photocatalytic degradationstudies were carried out using 25ndash200mg Lminus1 initial concen-tration of NB and 01 g Lminus1 of catalyst loading The plot ofdegradation for different solution concentration was madeand from Figure 7 it could be inferred that as concentrationincreased percentage degradation decreased This may bedue to the fact that with the increase in initial concentrationof NB while the irradiation period and catalyst dose arekept constant more NB molecules are present on the surfaceof TiO

2 Thus an increase in the number of substrate ions

accommodating in interlayer spacing inhibits the action ofthe catalyst which thereby decreases the number of reactive∙OH and O∙minus

2free radicals attacking the NB molecules and

hence lowers the photodegradation efficiency [23]

332 Effect of Light Intensity The influence of light intensityon the degradation efficiency has been examined at constantNitrobenzene concentration (50mg Lminus1) at pH (65) andcatalyst loading (01 g Lminus1) It is evident that the degradationrate increases with increase in the light intensity as shownin Figure 6 The photons required for the electron transferwere generated by UV irradiation which results in electrontransfer fromvalence band to conduction bandof the catalystThe degradation increases when more radiations fall on

0

10

20

30

40

50

60

70

80

90

050 100 150 200 250 300 350 400

Deg

rada

tion

()

Time (min)

25mgLminus1

75mgLminus1

150mgLminus1

50mgLminus1

100mgLminus1

200mgLminus1

Figure 7 Effect of solution concentration on degradation (lightintensity 500W pH 68 and catalyst dosage 01 g Lminus1)

the catalyst surface and hence more hydroxyl radicals areproduced [24]

333 Effect of Catalyst Dosage Photocatalyst dosage addedto the reaction vessel is a major parameter affecting thephotocatalytic degradation efficiency The aqueous solutionof 50mg Lminus1 of solution was degraded using different catalystdosages (0025 005 01 015 and 02 g Lminus1) From Figure 8it can be seen that maximum degradation was achieved forthe catalyst dosage of 01 g Lminus1 It could also be inferred thatfurther increase in catalyst dosage did not yield an increasein degradation percentage

International Journal of Photoenergy 7

68

70

72

74

76

78

80

0 005 01 015 02 025

Deg

rada

tion

()

Catalyst dosage (gLminus1)

Figure 8 Effect of catalyst dosage on degradation (Conc50mg Lminus1 pH 68 and intensity 500W)

The increase in degradation percentage for 0025 to01 g Lminus1 may be due to an increase in the amount of activesites on the surface of the photocatalyst particlesThe numberof NB molecules adsorbed as well as the number of photonsabsorbed increase with the increase in catalyst concentrationthereby enhancing the rate of degradation Addition ofcatalyst beyond 01 g Lminus1 leads to decrease in the degradationAggregation of TiO

2particles occurs at higher dosage causing

decrease in the number of surface active sites and also there isan increase in the opacity of the solution and light scatteringof TiO

2particles at high dosage through the solution [25]

334 Effect of pH of the Solution pH of the solution greatlyinfluences the degradation rate It tends to change the surfaceproperty of the catalyst The effect of change in initial pH(2 4 65 8 9 10 and 11) of 50mg Lminus1 of the nitrobenzenesolution was studied by adding 01 g Lminus1 of catalyst The plotof degradation against pH (Figure 9) showed that as pHincreased the degradation increased A maximum of 100degradation was achieved at pH 9The degradation was lowerin lower acidic and higher alkaline pH

pH of the catalyst dispersions majorly affects the surfaceproperties on the particles agglomerate size formed andthe conductance and valence bands positions [26] Thenitrobenzene solution was degraded by hydroxyl attack anddirect oxidation at the holes and reduction at the conductionband In alkaline pH the surface of TiO

2-Ce acquires a

negative charge leading to greater adsorption and henceincreasing the degradation rate in the alkaline media

335 Kinetic Modelling Using Langmuir Hinshelwood ModelThe degradation percentage was calculated and for hetero-geneous catalyst the Langmuir Hinshelwood model wasused to calculate the apparent rate constant The LangmuirHinshelwoodmodel derived based on themonolayer activityassumption was used to estimate the kinetic parameters in

72

74

76

78

80

82

84

86

0 2 4 6 8 10 12

Deg

rada

tion

()

Solution pH

Figure 9 Effect of solution pH on degradation (Conc 50mg Lminus1catalyst dosage 01 g Lminus1 and intensity 500W)

0

02

04

06

08

1

12

14

16

18

2

0 50 100 150 200 250 300 350 400Time (min)

25mgLminus1

75mgLminus1150mgLminus150mgLminus1100mgLminus1

200mgLminus1

ln(C

0C

)

Figure 10 Langmuir Hinshelwood plot (pH 68 catalyst dosage01 g Lminus1 and light intensity 500W)

terms of reaction rate constant (119896119903) and Langmuir Hinshel-

wood adsorption constant (119870LH) which is as given in

119903 =119896119903119870LH119862

1 + 119870LH1198620= 119896app119862 (8)

where is rate of disappearance of organic substratemg Lminus1minminus1 and 119862 is concentration of organic substratemg Lminus1

119896app =119896119903119870LH

1 + 119870LH1198620 (9)

Linearization of (8) yields an equation from which a plotof ln (119862

0119862) against time will result in a linear relation-

ship resulting in zero intercept and apparent rate constant(119896app) derived from the slope of the line Figure 10 is the

8 International Journal of Photoenergy

0

01

02

03

04

05

06

0 0001 0002 0003 0004 0005 0006

times10minus2

kap

p(m

inminus1) (

theo

)

kapp (minminus1) (exp)

Figure 11 Comparison between the experimental and theoreticalvalues of apparent rate constant

representation of the plot from which the apparent rateconstant was determined using slope of the line Similarlyfor all the conditions of pH (2ndash11) concentration (25ndash200mg Lminus1) catalyst dosage (0025ndash02 g Lminus1) and intensityof visible light (150ndash500W) the plot of ln (119862

0119862) against

time was evaluated The apparent rate constant was foundto increase with light intensity and decrease with solutionconcentrationThemaximum degradation could be achievedat the following parameter condition pH 9 dosage 01 g Lminus1solution concentration 25mg Lminus1 and light intensity 500WThe nonlinear fit between the apparent rate constant and theoperational parameters was determined and were found thatthe experimental values when compared with the theoreticalvalues as in Figure 11 the theoretical values had less than 3error and hence the following equation (10) could be chosenfor approximating the experimental conditions Equation(10) could be used for a condition of pH 2 to 9 dosageof 005 to 01 g Lminus1 light intensity of 150 300 or 500Wand concentration of solution from 25 to 200mg Lminus1 Thenonlinear equation was

119896app (theoretical)

= 0000229 lowast Intensity0584 lowast Concentrationminus0230

lowast Dosage0425 lowast pH0336(10)

4 Conclusion

The undoped and cerium doped titania photocatalyst wasprepared through the sol-gel route The cerium doped pho-tocatalyst could absorb the visible light and showed highphotoactivity in the visible region because of the band gapnarrowing Cerium atoms existed in the state of Ce

2O3

and were dispersed on the surface of titania suppressingthe recombination of electron-hole pairs and increasing thephotoactivity as confirmed using XPS and DRIFT analysis

The average crystal size and the surface area were deter-mined and compared between two types of catalysts Theoperational parameters were optimized and the followingcondition was suggested to obtain maximum degradationpH 9 dosage 01 g Lminus1 solution concentration 25mg Lminus1and light intensity 500W The kinetic study revealed thatthe degradation followed Langmuir Hinshelwood modelThe apparent rate constant was determined and evaluatedtheoretically using the nonlinear fit which depends on theoperational parameters Based on the previously mentionedexperiments and characterization it could be concluded thatCeriumdoped TiO

2catalyst prepared by solgelmethod could

be efficiently used for degradation of Nitrobenzene usingvisible light

References

[1] S C Moon H Mametsuka S Tabata and E Suzuki ldquoPhoto-catalytic production of hydrogen from water using TiO

2and

BTiO2rdquo Catalysis Today vol 58 no 2 pp 125ndash132 2000

[2] C Lettmann K Hildenbrand H Kisch W Macyk and WF Maier ldquoVisible light photodegradation of 4-chlorophenolwith a coke-containing titaniumdioxide photocatalystrdquoAppliedCatalysis B vol 32 no 4 pp 215ndash227 2001

[3] 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

[4] C-S Wu and C Chen ldquoA visible-light response vanadium-doped titania nanocatalyst by sol-gel methodrdquo Journal of Photo-chemistry and Photobiology A vol 163 no 3 pp 509ndash515 2004

[5] T Umebayashi T Yamaki S Tanaka and K Asai ldquoVisiblelight-induced degradation ofmethylene blue on S-doped TiO

2rdquo

Chemistry Letters vol 32 no 4 pp 330ndash331 2003[6] R J Tayade R G Kulkarni and R V Jasra ldquoPhotocatalytic

degradation of aqueous nitrobenzene by nanocrystalline TiO2rdquo

Industrial and Engineering Chemistry Research vol 45 no 3 pp922ndash927 2006

[7] M H Priya and G Madras ldquoPhotocatalytic degradation ofnitrobenzenes with combustion synthesized nano-TiO

2rdquo Jour-

nal of Photochemistry and Photobiology A vol 178 no 1 pp 1ndash72006

[8] S Ikeda N Sugiyama B Pal et al ldquoPhotocatalytic activityof transition-metal-loaded titanium(IV) oxide powders sus-pended in aqueous solutions correlation with electron-holerecombination kineticsrdquo Physical Chemistry Chemical Physicsvol 3 no 2 pp 267ndash273 2001

[9] A Fuerte M D Hernandez-Alonso A J Maira et al ldquoVisiblelight-activated nanosized doped-TiO

2photocatalystsrdquo Chemi-

cal Communications no 24 pp 2718ndash2719 2001[10] W Choi A Termin and M R Hoffmann ldquoThe role of

metal ion dopants in quantum-sized TiO2 correlation between

photoreactivity and charge carrier recombination dynamicsrdquoJournal of Physical Chemistry vol 98 no 51 pp 13669ndash136791994

[11] B M Reddy P M Sreekanth Y Yamada Q Xu and TKobayashi ldquoSurface characterization of sulfate molybdate andtungstate promoted TiO

2-ZrO2solid acid catalysts by XPS and

other techniquesrdquoApplied Catalysis A vol 228 no 1-2 pp 269ndash278 2002

International Journal of Photoenergy 9

[12] VMOrera R IMerino and F Pena ldquoCe3+harrCe4+ conversionin ceria-doped zirconia single crystals induced by oxido-reduction treatmentsrdquo Solid State Ionics vol 72 no 2 pp 224ndash231 1994

[13] W M Yen M Raukas S A Basun W Van Schaik and UHappek ldquoOptical and photoconductive properties of cerium-doped crystalline solidsrdquo Journal of Luminescence vol 69 no5-6 pp 287ndash294 1996

[14] S W Chen J M Lee K T Lu et al ldquoBand-gap narrowingof TiO

2doped with Ce probed with x-ray absorption spec-

troscopyrdquo Applied Physics Letters vol 97 no 1 Article ID012104 2010

[15] H Liu X Z Li Y J Leng andW Z Li ldquoAn alternative approachto ascertain the rate-determining steps of TiO

2photoelectro-

catalytic reaction by electrochemical impedance spectroscopyrdquoJournal of Physical Chemistry B vol 107 no 34 pp 8988ndash89962003

[16] D S Bhatkhande V G Pangarkar and A A C M BeenackersldquoPhotocatalytic degradation of nitrobenzene using titaniumdioxide and concentrated solar radiation chemical effects andscaleuprdquoWater Research vol 37 no 6 pp 1223ndash1230 2003

[17] M Saif and M S A Abdel-Mottaleb ldquoTitanium dioxidenanomaterial dopedwith trivalent lanthanide ions of Tb Eu andSm preparation characterization and potential applicationsrdquoInorganica Chimica Acta vol 360 no 9 pp 2863ndash2874 2007

[18] A Alouche ldquoPreparation and characterization of Copper andor Cerium catalysts supported on Alumina or Ceriardquo JordanJournal of Mechanical and Industrial Engineering vol 2 pp 111ndash116 2008

[19] R J Tayade P K Surolia R G Kulkarni and R V JasraldquoPhotocatalytic degradation of dyes and organic contaminantsin water using nanocrystalline anatase and rutile TiO

2rdquo Science

and Technology of AdvancedMaterials vol 8 no 6 pp 455ndash4622007

[20] X-Z Shen Z-C Liu S-M Xie and J Guo ldquoDegradationof nitrobenzene using titania photocatalyst co-doped withnitrogen and cerium under visible light illuminationrdquo Journalof Hazardous Materials vol 162 no 2-3 pp 1193ndash1198 2009

[21] WWang Y Huang and S Yang ldquoPhotocatalytic degradation ofnitrobenzene wastewater with H

3PW12O40TiO2rdquo in Proceed-

ings of the International Conference on Mechanic Automationand Control Engineering (MACE rsquo10) pp 1303ndash1305 June 2010

[22] P K Surolia R J Tayade and R V Jasra ldquoPhotocatalytic degra-dation of nitrobenzene in an aqueous system by transition-metal-exchanged ETS-10 zeolitesrdquo Industrial and EngineeringChemistry Research vol 49 no 8 pp 3961ndash3966 2010

[23] W Bahnemann M Muneer and M M Haque ldquoTitaniumdioxide-mediated photocatalysed degradation of few selectedorganic pollutants in aqueous suspensionsrdquoCatalysis Today vol124 no 3-4 pp 133ndash148 2007

[24] A E Cassano and O M Alfano ldquoReaction engineering of sus-pended solid heterogeneous photocatalytic reactorsrdquo CatalysisToday vol 58 no 2 pp 167ndash197 2000

[25] A A Adesina ldquoIndustrial exploitation of photocatalysis pro-gress perspectives and prospectsrdquo Catalysis Surveys from Asiavol 8 no 4 pp 265ndash273 2004

[26] Y Ku and C B Hsieh ldquoPhotocatalytic decomposition of 24-dichlorophenol in aqueous TiO

2suspensionsrdquoWater Research

vol 26 no 11 pp 1451ndash1456 1992

Impact Factor 173028 Days Fast Track Peer ReviewAll Subject Areas of ScienceSubmit at httpwwwtswjcom

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawi Publishing Corporation httpwwwhindawicom Volume 2013

The Scientific World Journal

International Journal of Photoenergy 7

68

70

72

74

76

78

80

0 005 01 015 02 025

Deg

rada

tion

()

Catalyst dosage (gLminus1)

Figure 8 Effect of catalyst dosage on degradation (Conc50mg Lminus1 pH 68 and intensity 500W)

The increase in degradation percentage for 0025 to01 g Lminus1 may be due to an increase in the amount of activesites on the surface of the photocatalyst particlesThe numberof NB molecules adsorbed as well as the number of photonsabsorbed increase with the increase in catalyst concentrationthereby enhancing the rate of degradation Addition ofcatalyst beyond 01 g Lminus1 leads to decrease in the degradationAggregation of TiO

2particles occurs at higher dosage causing

decrease in the number of surface active sites and also there isan increase in the opacity of the solution and light scatteringof TiO

2particles at high dosage through the solution [25]

334 Effect of pH of the Solution pH of the solution greatlyinfluences the degradation rate It tends to change the surfaceproperty of the catalyst The effect of change in initial pH(2 4 65 8 9 10 and 11) of 50mg Lminus1 of the nitrobenzenesolution was studied by adding 01 g Lminus1 of catalyst The plotof degradation against pH (Figure 9) showed that as pHincreased the degradation increased A maximum of 100degradation was achieved at pH 9The degradation was lowerin lower acidic and higher alkaline pH

pH of the catalyst dispersions majorly affects the surfaceproperties on the particles agglomerate size formed andthe conductance and valence bands positions [26] Thenitrobenzene solution was degraded by hydroxyl attack anddirect oxidation at the holes and reduction at the conductionband In alkaline pH the surface of TiO

2-Ce acquires a

negative charge leading to greater adsorption and henceincreasing the degradation rate in the alkaline media

335 Kinetic Modelling Using Langmuir Hinshelwood ModelThe degradation percentage was calculated and for hetero-geneous catalyst the Langmuir Hinshelwood model wasused to calculate the apparent rate constant The LangmuirHinshelwoodmodel derived based on themonolayer activityassumption was used to estimate the kinetic parameters in

72

74

76

78

80

82

84

86

0 2 4 6 8 10 12

Deg

rada

tion

()

Solution pH

Figure 9 Effect of solution pH on degradation (Conc 50mg Lminus1catalyst dosage 01 g Lminus1 and intensity 500W)

0

02

04

06

08

1

12

14

16

18

2

0 50 100 150 200 250 300 350 400Time (min)

25mgLminus1

75mgLminus1150mgLminus150mgLminus1100mgLminus1

200mgLminus1

ln(C

0C

)

Figure 10 Langmuir Hinshelwood plot (pH 68 catalyst dosage01 g Lminus1 and light intensity 500W)

terms of reaction rate constant (119896119903) and Langmuir Hinshel-

wood adsorption constant (119870LH) which is as given in

119903 =119896119903119870LH119862

1 + 119870LH1198620= 119896app119862 (8)

where is rate of disappearance of organic substratemg Lminus1minminus1 and 119862 is concentration of organic substratemg Lminus1

119896app =119896119903119870LH

1 + 119870LH1198620 (9)

Linearization of (8) yields an equation from which a plotof ln (119862

0119862) against time will result in a linear relation-

ship resulting in zero intercept and apparent rate constant(119896app) derived from the slope of the line Figure 10 is the

8 International Journal of Photoenergy

0

01

02

03

04

05

06

0 0001 0002 0003 0004 0005 0006

times10minus2

kap

p(m

inminus1) (

theo

)

kapp (minminus1) (exp)

Figure 11 Comparison between the experimental and theoreticalvalues of apparent rate constant

representation of the plot from which the apparent rateconstant was determined using slope of the line Similarlyfor all the conditions of pH (2ndash11) concentration (25ndash200mg Lminus1) catalyst dosage (0025ndash02 g Lminus1) and intensityof visible light (150ndash500W) the plot of ln (119862

0119862) against

time was evaluated The apparent rate constant was foundto increase with light intensity and decrease with solutionconcentrationThemaximum degradation could be achievedat the following parameter condition pH 9 dosage 01 g Lminus1solution concentration 25mg Lminus1 and light intensity 500WThe nonlinear fit between the apparent rate constant and theoperational parameters was determined and were found thatthe experimental values when compared with the theoreticalvalues as in Figure 11 the theoretical values had less than 3error and hence the following equation (10) could be chosenfor approximating the experimental conditions Equation(10) could be used for a condition of pH 2 to 9 dosageof 005 to 01 g Lminus1 light intensity of 150 300 or 500Wand concentration of solution from 25 to 200mg Lminus1 Thenonlinear equation was

119896app (theoretical)

= 0000229 lowast Intensity0584 lowast Concentrationminus0230

lowast Dosage0425 lowast pH0336(10)

4 Conclusion

The undoped and cerium doped titania photocatalyst wasprepared through the sol-gel route The cerium doped pho-tocatalyst could absorb the visible light and showed highphotoactivity in the visible region because of the band gapnarrowing Cerium atoms existed in the state of Ce

2O3

and were dispersed on the surface of titania suppressingthe recombination of electron-hole pairs and increasing thephotoactivity as confirmed using XPS and DRIFT analysis

The average crystal size and the surface area were deter-mined and compared between two types of catalysts Theoperational parameters were optimized and the followingcondition was suggested to obtain maximum degradationpH 9 dosage 01 g Lminus1 solution concentration 25mg Lminus1and light intensity 500W The kinetic study revealed thatthe degradation followed Langmuir Hinshelwood modelThe apparent rate constant was determined and evaluatedtheoretically using the nonlinear fit which depends on theoperational parameters Based on the previously mentionedexperiments and characterization it could be concluded thatCeriumdoped TiO

2catalyst prepared by solgelmethod could

be efficiently used for degradation of Nitrobenzene usingvisible light

References

[1] S C Moon H Mametsuka S Tabata and E Suzuki ldquoPhoto-catalytic production of hydrogen from water using TiO

2and

BTiO2rdquo Catalysis Today vol 58 no 2 pp 125ndash132 2000

[2] C Lettmann K Hildenbrand H Kisch W Macyk and WF Maier ldquoVisible light photodegradation of 4-chlorophenolwith a coke-containing titaniumdioxide photocatalystrdquoAppliedCatalysis B vol 32 no 4 pp 215ndash227 2001

[3] 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

[4] C-S Wu and C Chen ldquoA visible-light response vanadium-doped titania nanocatalyst by sol-gel methodrdquo Journal of Photo-chemistry and Photobiology A vol 163 no 3 pp 509ndash515 2004

[5] T Umebayashi T Yamaki S Tanaka and K Asai ldquoVisiblelight-induced degradation ofmethylene blue on S-doped TiO

2rdquo

Chemistry Letters vol 32 no 4 pp 330ndash331 2003[6] R J Tayade R G Kulkarni and R V Jasra ldquoPhotocatalytic

degradation of aqueous nitrobenzene by nanocrystalline TiO2rdquo

Industrial and Engineering Chemistry Research vol 45 no 3 pp922ndash927 2006

[7] M H Priya and G Madras ldquoPhotocatalytic degradation ofnitrobenzenes with combustion synthesized nano-TiO

2rdquo Jour-

nal of Photochemistry and Photobiology A vol 178 no 1 pp 1ndash72006

[8] S Ikeda N Sugiyama B Pal et al ldquoPhotocatalytic activityof transition-metal-loaded titanium(IV) oxide powders sus-pended in aqueous solutions correlation with electron-holerecombination kineticsrdquo Physical Chemistry Chemical Physicsvol 3 no 2 pp 267ndash273 2001

[9] A Fuerte M D Hernandez-Alonso A J Maira et al ldquoVisiblelight-activated nanosized doped-TiO

2photocatalystsrdquo Chemi-

cal Communications no 24 pp 2718ndash2719 2001[10] W Choi A Termin and M R Hoffmann ldquoThe role of

metal ion dopants in quantum-sized TiO2 correlation between

photoreactivity and charge carrier recombination dynamicsrdquoJournal of Physical Chemistry vol 98 no 51 pp 13669ndash136791994

[11] B M Reddy P M Sreekanth Y Yamada Q Xu and TKobayashi ldquoSurface characterization of sulfate molybdate andtungstate promoted TiO

2-ZrO2solid acid catalysts by XPS and

other techniquesrdquoApplied Catalysis A vol 228 no 1-2 pp 269ndash278 2002

International Journal of Photoenergy 9

[12] VMOrera R IMerino and F Pena ldquoCe3+harrCe4+ conversionin ceria-doped zirconia single crystals induced by oxido-reduction treatmentsrdquo Solid State Ionics vol 72 no 2 pp 224ndash231 1994

[13] W M Yen M Raukas S A Basun W Van Schaik and UHappek ldquoOptical and photoconductive properties of cerium-doped crystalline solidsrdquo Journal of Luminescence vol 69 no5-6 pp 287ndash294 1996

[14] S W Chen J M Lee K T Lu et al ldquoBand-gap narrowingof TiO

2doped with Ce probed with x-ray absorption spec-

troscopyrdquo Applied Physics Letters vol 97 no 1 Article ID012104 2010

[15] H Liu X Z Li Y J Leng andW Z Li ldquoAn alternative approachto ascertain the rate-determining steps of TiO

2photoelectro-

catalytic reaction by electrochemical impedance spectroscopyrdquoJournal of Physical Chemistry B vol 107 no 34 pp 8988ndash89962003

[16] D S Bhatkhande V G Pangarkar and A A C M BeenackersldquoPhotocatalytic degradation of nitrobenzene using titaniumdioxide and concentrated solar radiation chemical effects andscaleuprdquoWater Research vol 37 no 6 pp 1223ndash1230 2003

[17] M Saif and M S A Abdel-Mottaleb ldquoTitanium dioxidenanomaterial dopedwith trivalent lanthanide ions of Tb Eu andSm preparation characterization and potential applicationsrdquoInorganica Chimica Acta vol 360 no 9 pp 2863ndash2874 2007

[18] A Alouche ldquoPreparation and characterization of Copper andor Cerium catalysts supported on Alumina or Ceriardquo JordanJournal of Mechanical and Industrial Engineering vol 2 pp 111ndash116 2008

[19] R J Tayade P K Surolia R G Kulkarni and R V JasraldquoPhotocatalytic degradation of dyes and organic contaminantsin water using nanocrystalline anatase and rutile TiO

2rdquo Science

and Technology of AdvancedMaterials vol 8 no 6 pp 455ndash4622007

[20] X-Z Shen Z-C Liu S-M Xie and J Guo ldquoDegradationof nitrobenzene using titania photocatalyst co-doped withnitrogen and cerium under visible light illuminationrdquo Journalof Hazardous Materials vol 162 no 2-3 pp 1193ndash1198 2009

[21] WWang Y Huang and S Yang ldquoPhotocatalytic degradation ofnitrobenzene wastewater with H

3PW12O40TiO2rdquo in Proceed-

ings of the International Conference on Mechanic Automationand Control Engineering (MACE rsquo10) pp 1303ndash1305 June 2010

[22] P K Surolia R J Tayade and R V Jasra ldquoPhotocatalytic degra-dation of nitrobenzene in an aqueous system by transition-metal-exchanged ETS-10 zeolitesrdquo Industrial and EngineeringChemistry Research vol 49 no 8 pp 3961ndash3966 2010

[23] W Bahnemann M Muneer and M M Haque ldquoTitaniumdioxide-mediated photocatalysed degradation of few selectedorganic pollutants in aqueous suspensionsrdquoCatalysis Today vol124 no 3-4 pp 133ndash148 2007

[24] A E Cassano and O M Alfano ldquoReaction engineering of sus-pended solid heterogeneous photocatalytic reactorsrdquo CatalysisToday vol 58 no 2 pp 167ndash197 2000

[25] A A Adesina ldquoIndustrial exploitation of photocatalysis pro-gress perspectives and prospectsrdquo Catalysis Surveys from Asiavol 8 no 4 pp 265ndash273 2004

[26] Y Ku and C B Hsieh ldquoPhotocatalytic decomposition of 24-dichlorophenol in aqueous TiO

2suspensionsrdquoWater Research

vol 26 no 11 pp 1451ndash1456 1992

Impact Factor 173028 Days Fast Track Peer ReviewAll Subject Areas of ScienceSubmit at httpwwwtswjcom

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawi Publishing Corporation httpwwwhindawicom Volume 2013

The Scientific World Journal

8 International Journal of Photoenergy

0

01

02

03

04

05

06

0 0001 0002 0003 0004 0005 0006

times10minus2

kap

p(m

inminus1) (

theo

)

kapp (minminus1) (exp)

Figure 11 Comparison between the experimental and theoreticalvalues of apparent rate constant

representation of the plot from which the apparent rateconstant was determined using slope of the line Similarlyfor all the conditions of pH (2ndash11) concentration (25ndash200mg Lminus1) catalyst dosage (0025ndash02 g Lminus1) and intensityof visible light (150ndash500W) the plot of ln (119862

0119862) against

time was evaluated The apparent rate constant was foundto increase with light intensity and decrease with solutionconcentrationThemaximum degradation could be achievedat the following parameter condition pH 9 dosage 01 g Lminus1solution concentration 25mg Lminus1 and light intensity 500WThe nonlinear fit between the apparent rate constant and theoperational parameters was determined and were found thatthe experimental values when compared with the theoreticalvalues as in Figure 11 the theoretical values had less than 3error and hence the following equation (10) could be chosenfor approximating the experimental conditions Equation(10) could be used for a condition of pH 2 to 9 dosageof 005 to 01 g Lminus1 light intensity of 150 300 or 500Wand concentration of solution from 25 to 200mg Lminus1 Thenonlinear equation was

119896app (theoretical)

= 0000229 lowast Intensity0584 lowast Concentrationminus0230

lowast Dosage0425 lowast pH0336(10)

4 Conclusion

The undoped and cerium doped titania photocatalyst wasprepared through the sol-gel route The cerium doped pho-tocatalyst could absorb the visible light and showed highphotoactivity in the visible region because of the band gapnarrowing Cerium atoms existed in the state of Ce

2O3

and were dispersed on the surface of titania suppressingthe recombination of electron-hole pairs and increasing thephotoactivity as confirmed using XPS and DRIFT analysis

The average crystal size and the surface area were deter-mined and compared between two types of catalysts Theoperational parameters were optimized and the followingcondition was suggested to obtain maximum degradationpH 9 dosage 01 g Lminus1 solution concentration 25mg Lminus1and light intensity 500W The kinetic study revealed thatthe degradation followed Langmuir Hinshelwood modelThe apparent rate constant was determined and evaluatedtheoretically using the nonlinear fit which depends on theoperational parameters Based on the previously mentionedexperiments and characterization it could be concluded thatCeriumdoped TiO

2catalyst prepared by solgelmethod could

be efficiently used for degradation of Nitrobenzene usingvisible light

References

[1] S C Moon H Mametsuka S Tabata and E Suzuki ldquoPhoto-catalytic production of hydrogen from water using TiO

2and

BTiO2rdquo Catalysis Today vol 58 no 2 pp 125ndash132 2000

[2] C Lettmann K Hildenbrand H Kisch W Macyk and WF Maier ldquoVisible light photodegradation of 4-chlorophenolwith a coke-containing titaniumdioxide photocatalystrdquoAppliedCatalysis B vol 32 no 4 pp 215ndash227 2001

[3] 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

[4] C-S Wu and C Chen ldquoA visible-light response vanadium-doped titania nanocatalyst by sol-gel methodrdquo Journal of Photo-chemistry and Photobiology A vol 163 no 3 pp 509ndash515 2004

[5] T Umebayashi T Yamaki S Tanaka and K Asai ldquoVisiblelight-induced degradation ofmethylene blue on S-doped TiO

2rdquo

Chemistry Letters vol 32 no 4 pp 330ndash331 2003[6] R J Tayade R G Kulkarni and R V Jasra ldquoPhotocatalytic

degradation of aqueous nitrobenzene by nanocrystalline TiO2rdquo

Industrial and Engineering Chemistry Research vol 45 no 3 pp922ndash927 2006

[7] M H Priya and G Madras ldquoPhotocatalytic degradation ofnitrobenzenes with combustion synthesized nano-TiO

2rdquo Jour-

nal of Photochemistry and Photobiology A vol 178 no 1 pp 1ndash72006

[8] S Ikeda N Sugiyama B Pal et al ldquoPhotocatalytic activityof transition-metal-loaded titanium(IV) oxide powders sus-pended in aqueous solutions correlation with electron-holerecombination kineticsrdquo Physical Chemistry Chemical Physicsvol 3 no 2 pp 267ndash273 2001

[9] A Fuerte M D Hernandez-Alonso A J Maira et al ldquoVisiblelight-activated nanosized doped-TiO

2photocatalystsrdquo Chemi-

cal Communications no 24 pp 2718ndash2719 2001[10] W Choi A Termin and M R Hoffmann ldquoThe role of

metal ion dopants in quantum-sized TiO2 correlation between

photoreactivity and charge carrier recombination dynamicsrdquoJournal of Physical Chemistry vol 98 no 51 pp 13669ndash136791994

[11] B M Reddy P M Sreekanth Y Yamada Q Xu and TKobayashi ldquoSurface characterization of sulfate molybdate andtungstate promoted TiO

2-ZrO2solid acid catalysts by XPS and

other techniquesrdquoApplied Catalysis A vol 228 no 1-2 pp 269ndash278 2002

International Journal of Photoenergy 9

[12] VMOrera R IMerino and F Pena ldquoCe3+harrCe4+ conversionin ceria-doped zirconia single crystals induced by oxido-reduction treatmentsrdquo Solid State Ionics vol 72 no 2 pp 224ndash231 1994

[13] W M Yen M Raukas S A Basun W Van Schaik and UHappek ldquoOptical and photoconductive properties of cerium-doped crystalline solidsrdquo Journal of Luminescence vol 69 no5-6 pp 287ndash294 1996

[14] S W Chen J M Lee K T Lu et al ldquoBand-gap narrowingof TiO

2doped with Ce probed with x-ray absorption spec-

troscopyrdquo Applied Physics Letters vol 97 no 1 Article ID012104 2010

[15] H Liu X Z Li Y J Leng andW Z Li ldquoAn alternative approachto ascertain the rate-determining steps of TiO

2photoelectro-

catalytic reaction by electrochemical impedance spectroscopyrdquoJournal of Physical Chemistry B vol 107 no 34 pp 8988ndash89962003

[16] D S Bhatkhande V G Pangarkar and A A C M BeenackersldquoPhotocatalytic degradation of nitrobenzene using titaniumdioxide and concentrated solar radiation chemical effects andscaleuprdquoWater Research vol 37 no 6 pp 1223ndash1230 2003

[17] M Saif and M S A Abdel-Mottaleb ldquoTitanium dioxidenanomaterial dopedwith trivalent lanthanide ions of Tb Eu andSm preparation characterization and potential applicationsrdquoInorganica Chimica Acta vol 360 no 9 pp 2863ndash2874 2007

[18] A Alouche ldquoPreparation and characterization of Copper andor Cerium catalysts supported on Alumina or Ceriardquo JordanJournal of Mechanical and Industrial Engineering vol 2 pp 111ndash116 2008

[19] R J Tayade P K Surolia R G Kulkarni and R V JasraldquoPhotocatalytic degradation of dyes and organic contaminantsin water using nanocrystalline anatase and rutile TiO

2rdquo Science

and Technology of AdvancedMaterials vol 8 no 6 pp 455ndash4622007

[20] X-Z Shen Z-C Liu S-M Xie and J Guo ldquoDegradationof nitrobenzene using titania photocatalyst co-doped withnitrogen and cerium under visible light illuminationrdquo Journalof Hazardous Materials vol 162 no 2-3 pp 1193ndash1198 2009

[21] WWang Y Huang and S Yang ldquoPhotocatalytic degradation ofnitrobenzene wastewater with H

3PW12O40TiO2rdquo in Proceed-

ings of the International Conference on Mechanic Automationand Control Engineering (MACE rsquo10) pp 1303ndash1305 June 2010

[22] P K Surolia R J Tayade and R V Jasra ldquoPhotocatalytic degra-dation of nitrobenzene in an aqueous system by transition-metal-exchanged ETS-10 zeolitesrdquo Industrial and EngineeringChemistry Research vol 49 no 8 pp 3961ndash3966 2010

[23] W Bahnemann M Muneer and M M Haque ldquoTitaniumdioxide-mediated photocatalysed degradation of few selectedorganic pollutants in aqueous suspensionsrdquoCatalysis Today vol124 no 3-4 pp 133ndash148 2007

[24] A E Cassano and O M Alfano ldquoReaction engineering of sus-pended solid heterogeneous photocatalytic reactorsrdquo CatalysisToday vol 58 no 2 pp 167ndash197 2000

[25] A A Adesina ldquoIndustrial exploitation of photocatalysis pro-gress perspectives and prospectsrdquo Catalysis Surveys from Asiavol 8 no 4 pp 265ndash273 2004

[26] Y Ku and C B Hsieh ldquoPhotocatalytic decomposition of 24-dichlorophenol in aqueous TiO

2suspensionsrdquoWater Research

vol 26 no 11 pp 1451ndash1456 1992

Impact Factor 173028 Days Fast Track Peer ReviewAll Subject Areas of ScienceSubmit at httpwwwtswjcom

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawi Publishing Corporation httpwwwhindawicom Volume 2013

The Scientific World Journal

International Journal of Photoenergy 9

[12] VMOrera R IMerino and F Pena ldquoCe3+harrCe4+ conversionin ceria-doped zirconia single crystals induced by oxido-reduction treatmentsrdquo Solid State Ionics vol 72 no 2 pp 224ndash231 1994

[13] W M Yen M Raukas S A Basun W Van Schaik and UHappek ldquoOptical and photoconductive properties of cerium-doped crystalline solidsrdquo Journal of Luminescence vol 69 no5-6 pp 287ndash294 1996

[14] S W Chen J M Lee K T Lu et al ldquoBand-gap narrowingof TiO

2doped with Ce probed with x-ray absorption spec-

troscopyrdquo Applied Physics Letters vol 97 no 1 Article ID012104 2010

[15] H Liu X Z Li Y J Leng andW Z Li ldquoAn alternative approachto ascertain the rate-determining steps of TiO

2photoelectro-

catalytic reaction by electrochemical impedance spectroscopyrdquoJournal of Physical Chemistry B vol 107 no 34 pp 8988ndash89962003

[16] D S Bhatkhande V G Pangarkar and A A C M BeenackersldquoPhotocatalytic degradation of nitrobenzene using titaniumdioxide and concentrated solar radiation chemical effects andscaleuprdquoWater Research vol 37 no 6 pp 1223ndash1230 2003

[17] M Saif and M S A Abdel-Mottaleb ldquoTitanium dioxidenanomaterial dopedwith trivalent lanthanide ions of Tb Eu andSm preparation characterization and potential applicationsrdquoInorganica Chimica Acta vol 360 no 9 pp 2863ndash2874 2007

[18] A Alouche ldquoPreparation and characterization of Copper andor Cerium catalysts supported on Alumina or Ceriardquo JordanJournal of Mechanical and Industrial Engineering vol 2 pp 111ndash116 2008

[19] R J Tayade P K Surolia R G Kulkarni and R V JasraldquoPhotocatalytic degradation of dyes and organic contaminantsin water using nanocrystalline anatase and rutile TiO

2rdquo Science

and Technology of AdvancedMaterials vol 8 no 6 pp 455ndash4622007

[20] X-Z Shen Z-C Liu S-M Xie and J Guo ldquoDegradationof nitrobenzene using titania photocatalyst co-doped withnitrogen and cerium under visible light illuminationrdquo Journalof Hazardous Materials vol 162 no 2-3 pp 1193ndash1198 2009

[21] WWang Y Huang and S Yang ldquoPhotocatalytic degradation ofnitrobenzene wastewater with H

3PW12O40TiO2rdquo in Proceed-

ings of the International Conference on Mechanic Automationand Control Engineering (MACE rsquo10) pp 1303ndash1305 June 2010

[22] P K Surolia R J Tayade and R V Jasra ldquoPhotocatalytic degra-dation of nitrobenzene in an aqueous system by transition-metal-exchanged ETS-10 zeolitesrdquo Industrial and EngineeringChemistry Research vol 49 no 8 pp 3961ndash3966 2010

[23] W Bahnemann M Muneer and M M Haque ldquoTitaniumdioxide-mediated photocatalysed degradation of few selectedorganic pollutants in aqueous suspensionsrdquoCatalysis Today vol124 no 3-4 pp 133ndash148 2007

[24] A E Cassano and O M Alfano ldquoReaction engineering of sus-pended solid heterogeneous photocatalytic reactorsrdquo CatalysisToday vol 58 no 2 pp 167ndash197 2000

[25] A A Adesina ldquoIndustrial exploitation of photocatalysis pro-gress perspectives and prospectsrdquo Catalysis Surveys from Asiavol 8 no 4 pp 265ndash273 2004

[26] Y Ku and C B Hsieh ldquoPhotocatalytic decomposition of 24-dichlorophenol in aqueous TiO

2suspensionsrdquoWater Research

vol 26 no 11 pp 1451ndash1456 1992

Impact Factor 173028 Days Fast Track Peer ReviewAll Subject Areas of ScienceSubmit at httpwwwtswjcom

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawi Publishing Corporation httpwwwhindawicom Volume 2013

The Scientific World Journal

Impact Factor 173028 Days Fast Track Peer ReviewAll Subject Areas of ScienceSubmit at httpwwwtswjcom

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawi Publishing Corporation httpwwwhindawicom Volume 2013

The Scientific World Journal