Research Article Photoelectrocatalytic Performance of ...downloads.hindawi.com/journals/ijp/2013/567426.pdf · To overcome these defects, considerable e ort has been ... It was also

Hindawi Publishing CorporationInternational Journal of PhotoenergyVolume 2013 Article ID 567426 7 pageshttpdxdoiorg1011552013567426

Research ArticlePhotoelectrocatalytic Performance of Benzoic Acid on TiO2Nanotube Array Electrodes

Hongchong Chen Jinhua Li Quanpeng Chen Di Li and Baoxue Zhou

School of Environmental Science and Engineering Shanghai Jiao Tong University Shanghai 200240 China

Correspondence should be addressed to Baoxue Zhou zhoubaoxuesjtueducn

Received 4 February 2013 Revised 22 April 2013 Accepted 22 April 2013

Academic Editor Jiaguo Yu

Copyright copy 2013 Hongchong Chen et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

The photoelectrocatalytic performance of benzoic acid on TiO2nanotube array electrodes was investigated A thin-cell was used to

discuss the effect of the bias voltage illumination intensity and electrolyte concentration on the photoelectrocatalytic degradationefficiency of benzoic acid The photogenerated current-time (I-t) profiles were found to be related to the adsorption and thedegradation process The relationship between the initial concentration and the photocurrent peaks (1198680ph) fits the Langmuir-typeadsorption model thus confirming that the adsorption of benzoic acid on TiO

2nanotube arrays (TNAs) was single monolayer

adsorption At low concentrations the I-t profiles simply decay after the initial transient peak due to the sufficient holes on theTNAs which would oxidize the benzoic acid quickly However the I-t profiles varied with increasing benzoic acid concentrationsbecause the rate of diffusion in the bulk solution and the degradation of the intermediate products affect the photoelectrocatalysison the electrode surface

1 Introduction

For nearly three decades the photocatalytic and photo-electrocatalytic degradation of organic substances on wide-bandgap semiconductive TiO

2nanomaterials have drawn

considerable attention because of their high photocatalyticefficiency nontoxicity nonphotocorrosiveness favorable bio-logical and chemical inertness and low cost [1ndash5] Howeverconventional TiO

2nanoparticles also exhibit defects such as

a high electron-hole recombination rate low photocatalyticdegradation efficiency and difficult follow-up process [6]

To overcome these defects considerable effort has beendevoted to improving the photocatalytic ability of TiO

2

catalysts including the synthesis of new TiO2structures [7ndash

11] TiO2nanotube arrays (TNAs) have gained attention and

have been successfully applied to the photoelectrocatalyticdegradation of a variety of organic pollutants because oftheir peculiar architecture large surface area high adsorptioncapacity easy teleportation and highly efficient degradationof organics [12ndash15]

Traditional studies on the photoelectrocatalytic oxidationof organic compounds were mainly performed in bulk

reactors wherein the pollutant concentration was repeatedlydetermined over a certain period via absorption spectropho-tometry [16ndash18] However this method limits the in-depthinvestigation of the reaction mechanism because of therelatively large body solution and long diffusion channel [19]The use of a thin-cell with a small-volume cavity facilitatedthe study of the adsorption characteristics of organic sub-stances and their interactions with the catalyst because of thesubsequent increase in the ratio of the photoanode area tothe organic solution volume These studies led to the rapidcompletion of the exhaustive redox reaction [19 20]

Benzoic acid was typical aromatic ring acid compound Itwas the most commonly used food preservative and antibac-terial agent [21] It was also extensively used in the printingand dyeing industry (as a mordant of dyeing and printing)as well as in the pharmaceutical (as the intermediate) [22]steel (as an antirust agent) [23] and other industries [24] Inaddition benzoic acid is the intermediate metabolic productof various aromatic compounds and also the degradationintermediate product of many complex refractory organics[25] However few reports on the photoelectrocatalytic per-formance of benzoic acid compounds have been released

2 International Journal of Photoenergy

In this paper the photoelectrocatalytic performance ofbenzoic acid on TNA electrodes was investigated using athin-cell reactor The adsorption properties microcosmicdegradation process and reaction characterization of benzoicacid on TNAs were investigated by analyzing the change inthe photogenerated current-time (119868ph-119905) profilesThe result ofthis study provides a solid foundation for future research intothe reaction mechanism and reaction kinetics of aromaticorganic compounds on TNA electrode surfaces

2 Materials and Methods

21Materials Titanium sheets (025mm thick 999purity)were purchased from Sumitomo Chemical (Japan) Unlessotherwise indicated reagents were obtained from SinopharmChemical Reagent Company and were used as receivedHigh-purity deionised water was used in the preparation ofall solutions

22 Preparation of TiO2Nanotube Array Electrode The

preparing method of TiO2nanotube array electrodes has

been published in our previous work [18] Hence only keypoints of the fabrication process were summarized hereThe electrolyte contain 01molL NaF 1molL NaHSO

4and

02molL trisodium citrate also with NaOH added to adjustthe pH The TiO

2nanotube array electrodes are prepared

under constant stirring for 4 h After anodization the as-prepared sample was washed with high-purity deionizedwater and dried at room temperature Then it was annealedin a laboratory muffle furnace at 500∘C to crystallize inthe air ambience X-ray diffraction (Bruker D8 ADVANCEGermany) analysis showed that the crystal structure of TNAis anatase [18]

23 Apparatus and Methods All experiments were per-formed at room temperature in a three-electrode electro-chemical cell with a quartz window (082 cm2)The thicknessof the spacer was 01mm which defined the cell volume of82120583LThe structure of thin-cell reactor has been reported inour previous paper [18] The TiO

2nanotube array electrode

was used as a working electrode a saturated AgAgClelectrode and a platinum foil were used as the reference andthe counter electrodes respectively Also 2molLNaNO

3was

chosen as the supporting electrolyte in the experiment Thesupply bias and work current are controlled by a CHI (CHInstrument Inc CHI601d USA) electrochemical analyzer2W LED UV lamp (365 nm) was chosen as UV light sourceThe light intensity in experiment was measured by UV-Aultraviolet irradiator

3 Results and Discussion

31 The Photocurrent-Time Profile Property and Net ChargeDetermined in Thin-Cell In the photoelectrochemical reac-tion the oxidation of organic compounds at the electrodes

can be represented by the following electrode reaction equa-tion

C119910H119898O119895N119896X119902+ (2119910 minus 119895)H

2O

997888rarr 119910CO2+ 119902Xminus + 119896NH

3

+ (4119910 minus 2119895 + 119898 minus 3119896)H+

+ (4119910 minus 2119895 + 119898 minus 3119896 minus 119902) eminus

(1)

where X represents the halogen atom The numbers ofcarbon hydrogen oxygen nitrogen and halogen atoms inthe organic compound are represented by 119910119898 119895 119896 and 119902

Faradayrsquos law can be used to quantify the concentrationby measuring the charge passed if the organics is completelyoxidized That is

119876net = int 119868 119889119905 = 119899119865119881119862 (2)

where 119868 is the photocurrent from the oxidation of the organicsand 119905 is the time elapsed upon illumination 119876net is thedirect measure of net charge of the organics 119899 is the numberof electrons transferred and 119862 is the concentration of theorganics while the volume (V) and the Faraday constant (F)are known constants

Figure 1 shows a set of typical photocurrent-time profilesin the exhaustive mode in thin-cell at the fixed applied biaspotential of 25 V Figures 1(c) and 1(d) show the photocurrentresponse of a blank solution of 20molL NaNO

3and a

20molL NaNO3solution containing 04mmolL benzoic

acid in a thin-cell in the absence of illumination (electro-catalytic performances) The results show that there is nophotocurrent under dark conditions which indicate that thebenzoic acid in thin-cell cannot be oxidized Figure 1(a)shows the typical photocurrent response of a blank solu-tion of 20molL NaNO

3under the illumination conditions

(79mWcm2) The even photocurrent (119868blank) observed forthe blank solution originated from the stable oxidation ofwater Figure 1(b) shows the photocurrent response of a20molL NaNO

3solution containing 04mmolL benzoic

acid in a thin-cell under the same illumination (79mWcm2)The total photocurrent (119868total) observed for the benzoicacid solution was the total of two different componentsone originates from the photoelectrocatalytic oxidation ofbenzoic acid whereas the other was from water oxidationwhich was the same as 119868blank (Figure 1(a)) When the 119868totaldecreases to the level of 119868blank the oxidation of organics wasfinished Hence the processes of the photoelectrochemicalreaction in thin-cell were described by the change of I-tprofile

The net charge which originated from the oxidationof organics was defined as 119876net which can be obtainedby subtracting 119876blank from 119876total The net charge whichobtained by (2) was defined as 119879ℎ119876net Because the changeof net charge is directly related to concentration of organicsduring the photoelectrochemical reaction The degradationefficiency (DE) of the photoelectrochemical reaction can bedefined as the ratio of 119876net to 119879ℎ119876net which can be used indescribing the property of thin-cell

International Journal of Photoenergy 3

00004

00003

00002

00001

0

0 30 60 90 120119905 (s)

119868ph

(A)

ab

c

a b

c

d

d

119868total

119868blank

119876net = 119876total minus 119876blank

Figure 1 Typical photocurrent-time responses obtained from thethin-cell (a) 20molL NaNO

3solution under illumination (b)

20molLNaNO3with 04mmolL benzoic acid under illumination

(c) 20molL NaNO3solution under no illumination (d) 20molL

NaNO3with 04mmolL benzoic acid under no illumination

According to (1) the stoichiometric oxidation of benzoicacid can be represented as

C7H6O2+ 12H

2O 997888rarr 7CO

2+ 30H+ + 30eminus (3)

That is if the complete mineralisation of benzoic acid hasbeen achieved 1mol of benzoic acid requires 30mol ofelectrons The relationship between the net charge and theconcentration should be written as follows with the cellvolume 119881 = 82 120583L being used

119879ℎ119876net = 30119865119881119862 = 00237119862 (4)

Hence the 119879ℎ119876net of 02mmolL 04mmolL and08mmolL were 000474mC and 000948mC 001896mC

32 Effect of Photoelectrocatalytic Degradation onBenzoic Acid

321 Effect of the Bias Voltage The cyclic voltammogramsof a 20molL NaNO

3solution is shown in Figure 2 The

photocurrent increases with the bias voltage indicating thatthe bias voltage can improve the electronic transmission per-formance of TNAs in the thin-cell This increase may affectthe photoelectrocatalytic degradation efficiency of benzoicacid In the low-bias voltage range (lt2V) the photocurrentrapidly increases with the bias voltage thus demonstratingthat the photogenerated electrons cannot be completelyexported to the external circuit When the bias voltage isbetween 2 and 4V the photocurrent appears in a saturatedplatform indicating that the photogenerated electrons havebeen completely exported and that the recombination ofelectrons and holes has been restricted After the platformbecomes saturated (gt4V) the photocurrent again increaseswith the bias voltage and can cause the water molecules

00008

00006

00004

00002

0

minus00002

Curr

ent (

A)

0 1 2 3 4 5 6Potential (V)

Figure 2 Cyclic voltammograms of a 20molL NaNO3blank

solution in a thin-cell reactor based on the TNA electrodes underilluminations of 79mWcm2

to decompose when the bias voltage reaches the oxygenevolution potential of the TNA electrode The results inFigure 3 support this view

Figure 3 shows the photocurrent-time profile of benzoicacid (04mmolL) degradation at different bias voltagesand under 79mWcm2 ultraviolet (UV) illuminations Asshow in Figure 3 when the bias voltage is below 3V thedegradation time of benzoic acid decreased as the bias voltageincreased This was indicated that the increase in the biasvoltage can also improve the degradation rate of benzoic acidon TNAs However the photocurrent curve continuouslyincreases when the bias voltage is 4V which leads to failurein identifying the reaction termination using a computerThis result indicates that the degradation of benzoic acid issignificantly perturbed by the water decomposition when thebias voltage is too high

Table 1 shows the 119876net value and degradation efficiency(DE) of benzoic acid under different bias voltages When thebias voltage is below 2V the DE of benzoic acid increaseswith the bias voltage indicating that the application of abias voltage can enhance the photoelectrocatalytic capabilityof TNAs for benzoic acid When the bias voltage is setbetween 2 and 3V the degradation efficiency of benzoicacid exceeds 995 indicating that the benzoic acid iscompletely degraded The 119876net value remains stable in thiscondition indicating that the value of 119876net is related only tothe transferred electronics during the photoelectrocatalyticoxidationTherefore the bias voltage should be set within theelectrochemical window (2V to 3V)

322 Effect of Light Intensity Figure 4 shows the photocur-rent responses of a 2molL NaNO

3blank solution containing

benzoic acid (04mmolL) under different light intensitiesThe more intense the light the shorter the time for completedegradation indicating that an increase in the intensity oflight is conducive to promoting the photoelectrocatalyticdegradation rate


00004

00003

00002

000010 40 80 120 160

Time (s)

Curr

ent (

A)

Potential bias4 V3 V25 V

2 V15 V1 V

Figure 3 Photocurrent responses of a 2molL NaNO3blank

solution containing benzoic acid (04mmolL) in the thin-cellreactor based on the TNA electrodes at different fixed applied biaspotentials under bias voltages under illuminations of 79mWcm2

Figure 4 shows that the photocurrent increases with thelight intensity indicating that the increases of light intensitycan improve the electronic transmission performance ofTNAs The photocurrent-time curve shapes vary with thelight intensity demonstrating that the light intensity affectsthe photoelectrocatalysis of benzoic acid on TNAs

Table 2 shows that the 119876net and degradation efficiencyof 08mmolL benzoic acid increase with the light intensitywhen the light intensity is below 553mWcm2 This resultindicates that benzoic acid is not completely mineralizedbecause of the insufficient light intensity not inducing enoughelectron-hole pairs of TNAs in the thin-cell

However the 119876net of benzoic acid at low concentrations(02 and 04mmolL) and at 08mmolL under sufficientlight intensity (above 553mWcm2) remain comparativelyconstant confirming that 119876net is not related to the lightintensity but is associated with the transferred electrons inthe photoelectric catalytic oxidation when benzoic acid iscompletely mineralized

323 Effect of Electrolyte Concentration The transfer ofelectrons in the thin-cell reactor was affected by the elec-trolyte solution The voltammograms of 04mmolL ben-zoic acid with different NaNO

3concentrations under light

(79mWcm2) are shown in Figure 5 The photocurrentrapidly increases with the voltage when the NaNO

3concen-

tration is below 1molL indicating that the photoinducedelectrons are not completely exported to the external circuitWhen the concentration exceeds 15molL the photocurrentexhibits a saturated platform indicating that the photo-generated electrons are completely exported and that therecombination of electrons and holes is restrictedThe higherthe electrolyte concentration the stronger the conductivity

Table 1 119876net value and degradation efficiency (DE) under differentbias voltages

Bias voltage (V) 1 15 2 25 3119876net (mC) 0008511 0009048 0009433 0009469 0009443DE () 9020 9545 9950 9988 9961

00004

00005

00003

00002

00001

Curr

ent (

A)

The intensity of light (mWcm2)158118579

553316158

0 30 60 90 120Time (s)

Figure 4 Photocurrent responses of a 2molL NaNO3blank solu-

tion containing benzoic acid (04mmolL) in the thin-cell reactorbased on the TNA electrodes at the fixed applied bias potential of25 V under different light intensities

Table 3 shows that 119876net gradually increases with theelectrolyte concentration and is lower than 119879ℎ119876net whenthe NaNO

3electrolyte concentration is below 1molL These

results indicate that benzoic acid cannot be completelydegraded because of the insufficient number of hole onTNAs When the NaNO

3electrolyte concentration exceeds

15molL119876net remains stable and close to 119879ℎ119876net indicatingthat benzoic acid has been completely degraded because ofthe sufficient number of holes in this condition

33 Photoelectrocatalytic Degradation Property and Mecha-nism of Benzoic Acid The photocurrent response profiles ofbenzoic acid for seven different concentrations in the thin-cell reactor are shown in Figure 6 A comparison between119876net and 119879ℎ119876net shows that the different concentrationsof benzoic acid have all been completely degraded in aphotoelectrocatalytic manner

The relationship between the initial organic concentra-tions and 119868

0ph was used to analyze the adsorption prop-erties of benzoic acid on TNAs because the 119868

0ph valuecorresponds to the initial degradation rate according tothe principle of photoelectric catalysis Figure 6(a) showsthat the peak photocurrent (119868

0ph) increases with 1198620 At loworganic concentrations 119868

0ph is proportional to 1198620 possibly

because of the photohole capture process during benzoic acidmineralization However as the benzoic acid concentration


Table 2 119876net value and degradation efficiency (DE) of different concentrations of benzoic acid under varying light intensities

Concentration(mmolL)

Light intensities(mWcm2) 158 316 553 79 1185 158

02 119876net (mC) 0009423 0009434 0009421 0009467 0009449 0009409DE () 9947 9952 9938 9986 9967 9925

04 119876net (mC) 0009471 0009454 0009513 0009470 0009406 0009433DE () 9990 9972 10034 9989 9921 9950

08 119876net (mC) 0008552 0009075 0009434 0009445 0009466 0009429DE () 9021 9573 9952 9963 9985 9946

00006

00004

00002

0

Curr

ent (

A)

0 1 2 3 4Voltage (V)

The concentration of electrolyte (molL)4215

10502

Figure 5 Voltammograms of different concentrations of NaNO3

blank solution containing benzoic acid (04mmolL) in the thin-cell reactor based on the TNA electrodes under illumination of79mWcm2

Table 3 119876net and degradation efficiency of 04mmolL benzoicacid with different NaNO3 concentrations under illumination of79mWcm2 and a fixed applied bias voltage of 25 V

Electrolyteconcentration (molL) 05 1 15 2

119876net (mC) 0008112 0009260 0009415 0009436DE () 8557 9768 9931 9954

increases to a certain level photohole generation becomesthe rate-limiting step and the increase in 119868

0ph begins to slowdown

The relationship between 1198680ph and1198620 was simulated using

a computer as follows

1198680ph =4 times 10

minus5times 106119862

0

1 + 1061198620

+ 00003 1198772= 09945 (5)

The data (4) fit the Langmuir adsorption isothermTheseresults confirm that the adsorption behavior of benzoic acidon the TNAs is that of a monolayer adsorption

00004

000036

000032

000028

119868ph

(A)

119905 (s)0 20 40 60 80 100

04 mmolL03 mmolL02 mmolL01 mmolL

007 mmolL002 mmolL001 mmolLBaseline

000034

000032

00003

0 01 02 03 041198620 (mmolL)

(a)

1198680p

h(A

)

Figure 6 Photocurrent response profiles derived from the pho-toelectrocatalytic oxidation of different concentrations of benzoicacid in the thin-cell reactor based on the TNA electrodes (a)Relationship between the initial concentration (119862

0) and the net peak

photocurrent (1198680ph) of the TNA electrode for benzoic acid

The photocurrent response profiles of benzoic acid atseven different concentrations are shown in Figure 6 Thedegradation I-t profiles all show decay to a stable value How-ever this decay varies with increasing concentrations therebyillustrating the disparities in the photoelectrocatalytic processas well as the mechanism of benzoic acid degradation atdifferent concentrations

At low concentrations (0mmolL to 002mmolL) thetransient photocurrent rapidly reaches its peak at the initialstage because of the rapid degradation of the benzoic acidoriginally adsorbed on the TNA surface The photocurrentthen begins to decrease because of benzoic acid mineraliza-tion After a certain period the photocurrent finally reaches astable value and overlaps with 119868blankThis result indicates thatthe photoelectrocatalytic degradation of benzoic acid in thethin-cell reactor is complete

When the benzoic acid concentration reaches an interme-diate level (007mmolL to 01mmolL) the curve continuesincreasing after the initial peak possibly because of the


degradation of the intermediates Figure 6(a) shows that theadsorption of the electrode surface has not reached saturationat that point indicating that the number of photogeneratedholes on the electrode surface is sufficient Thus the rapidoxidation of intermediate products which can be more easilyoxidized than benzoic acid may have caused the current toincrease

As the concentration increases to levels above 02mmolL(01mmolL eg) the 119868-119905 profiles can be divided into fivemajor processes a rapid increase to the transient pho-tocurrent spikes a continuous increase a rapid decreasea reincrease and a decrease to a stable value MeanwhileFigure 6(a) shows that the adsorption on the TNAs hasreached saturation indicating that the holes on the TNAelectrode surface cannot oxidate all benzoic acid on theTNAs simultaneously This photoelectrocatalytic process canbe explained as follows In the initial stage the benzoic acidmolecule on the surface of the TNA electrode is rapidlyoxidized and the photocurrent rapidly reaches the initialpeak After the first oxidization the resting benzoic acidabsorbed on the TNA surface at elevated concentrations aswell as the intermediate products is oxidized which resultsin the continuous increase of the curve for benzoic acid afterthe initial peak The benzoic acid concentration cannot besupplemented in time because the rate of adsorption may beslower than the speed of degradation Therefore the opticalcurrent rapidly decreases After a certain period the areacovered by the benzoic acid absorbents begins to increasewhich results in a re-increase in the current Afterward thebenzoic acid concentration decreases which results in thedecrease in the photocurrent These findings indicate thatwhen the benzoic acid concentration is high the diffusionof benzoic acid in the bulk solution of the reactor as well asthe degradation of intermediate products from benzoic aciddecomposition would affect the photoelectrocatalysis on theelectrode surface

4 Conclusions

Thephotoelectrocatalytic performance of benzoic acid on theTiO2nanotube array electrode was investigated using a thin-

cell reactor The adsorption degradation rate and reactioncharacteristics of benzoic acid degradation were discussedby analyzing the changes in the photogenerated I-t profilesThe result of this paper provides a solid foundation for futureresearch into the degradation characteristics reaction mech-anism and reaction kinetics of aromatic organic compoundson the TNA electrode surface

Acknowledgments

The project was supported by the National High Technol-ogy Research and Development Program of China (863)(2009AA063003) the National Natural Science Foundationof China (no 20 677039) and RampD Foundation of ShanghaiJiaotong University The authors are for support of XRD labin Instrumental Analysis Center of SJTU

References

[1] J H Carey J Lawrence and H M Tosine ldquoPhotodechlorina-tion of PCBrsquos in the presence of titanium dioxide in aqueoussuspensionsrdquo Bulletin of Environmental Contamination andToxicology vol 16 no 6 pp 697ndash701 1976

[2] D H Kim and M A Anderson ldquoPhotoelectrocatalytic degra-dation of formic acid using a porous TiO

2thin-film electroderdquo

Environmental Science and Technology vol 28 no 3 pp 479ndash483 1994

[3] X Z Li H L Liu P T Yue and Y P Sun ldquoPhotoelectrocatalyticoxidation of rose Bengal in aqueous solution using a TiTiO

2

mesh electroderdquo Environmental Science and Technology vol 34no 20 pp 4401ndash4406 2000

[4] H L Liu D Zhou X Z Li and P T Yue ldquoPhotoelectrocatalyticdegradation of Rose Bengalrdquo Journal of Environmental Sciencesvol 15 no 5 pp 595ndash599 2003

[5] S Dezhl C Sheng J S Chung D Xiaodong and Z ZhibinldquoPhotocatalytic degradation of toluene using a novel flowreactor with Fe-doped TiO

2catalyst on porous nickel sheetsrdquo

Photochemistry and Photobiology vol 81 no 2 pp 352ndash3572005

[6] J Bai J H Li Y B Liu B X Zhou andWM Cai ldquoA new glasssubstrate photoelectrocatalytic electrode for efficient visible-light hydrogen production CdS sensitized TiO

2nanotube

arraysrdquo Applied Catalysis B vol 95 no 3-4 pp 408ndash413 2010[7] Y X Li Y Xiang S Q Peng X W Wang and L Zhou

ldquoModification of Zr-doped titania nanotube arrays by ureapyrolysis for enhanced visible-light photo electrochemical H

2

generationrdquo Electrochimica Acta vol 87 no 1 pp 794ndash8002013

[8] D W Gong C A Grimes O K Varghese et al ldquoTitaniumoxide nanotube arrays prepared by anodic oxidationrdquo Journalof Materials Research vol 16 no 12 pp 3331ndash3334 2001

[9] ZH Xu and J G Yu ldquoVisible-light-induced photoelectrochem-ical behaviors of Fe-modifiedTiO

2nanotube arraysrdquoNanoscale

vol 3 no 8 pp 3138ndash3144 2011[10] G P Dai J G Yu and G Liu ldquoSynthesis and enhanced visible-

light photoelectrocatalytic activity of p-N junction BiOITiO2

nanotube arraysrdquo Journal of Physical Chemistry C vol 115 no15 pp 7339ndash7346 2011

[11] Z H Xu J G Yu and G Liu ldquoEnhancement of ethanolelectrooxidation on plasmonic AuTiO

2nanotube arraysrdquo Elec-

trochemistry Communications vol 13 no 11 pp 1260ndash12632011

[12] W B Zhang T C An X M Xiao et al ldquoPhotoelectrocatalyticdegradation of reactive brilliant orange K-R in a new continu-ous flow photoelectrocatalytic reactorrdquo Applied Catalysis A vol255 no 2 pp 221ndash229 2003

[13] T An G Li X Zhu J Fu G Sheng and Z Kun ldquoPhoto-electrocatalytic degradation of oxalic acid in aqueous phasewith a novel three-dimensional electrode-hollow quartz tubephotoelectrocatalytic reactorrdquo Applied Catalysis A vol 279 no1-2 pp 247ndash256 2005

[14] QQMeng J GWangQ Xie HQDong andXN Li ldquoWatersplitting on TiO

2nanotube arraysrdquoCatalysis Today vol 165 no

1 pp 145ndash149 2011[15] C H Wang X T Zhang C L Shao et al ldquoRutile TiO

2

nanowires on anatase TiO2

nanofibers a branched het-erostructured photocatalysts via interface-assisted fabricationapproachrdquo Journal of Colloid and Interface Science vol 363 no1 pp 157ndash164 2011


[16] L Gu F Y Song andNW Zhu ldquoAn innovative electrochemicaldegradation of 1-diazo-2-naphthol-4-sulfonic acid in the pres-ence of Bi

2Fe4O9rdquo Applied Catalysis B vol 110 no 2 pp 186ndash

194 2011[17] J Krysa GWaldner HMestrsquoankova J Jirkovsky and G Grab-

ner ldquoPhotocatalytic degradation of model organic pollutantson an immobilized particulate TiO

2layer Roles of adsorption

processes andmechanistic complexityrdquoApplied Catalysis B vol64 no 3-4 pp 290ndash301 2006

[18] X J Yu Y QWang Z L Li S Bai and D Sun ldquoStudy on deac-tivated mechanism and regeneration methods of TiO

2during

photocatalytic benzoic acidrdquoActa Scientiae Circumstantiae vol26 no 3 pp 433ndash437 2006

[19] Q Zheng B X Zhou J Bai et al ldquoSelf-organized TiO2nan-

otube array sensor for the determination of chemical oxygendemandrdquo Advanced Materials vol 20 no 5 pp 1044ndash10492008

[20] J L Zhang B X Zhou Q Zheng et al ldquoPhotoelectrocatalyticCOD determination method using highly ordered TiO

2nan-

otube arrayrdquoWater Research vol 43 no 7 pp 1986ndash1992 2009[21] D S Ling H Y Xie Y Z He W E Gan and Y Gao ldquoDeter-

mination of preservatives by integrative coupling method ofheadspace liquid-phase microextraction and capillary zoneelectrophoresisrdquo Journal of Chromatography A vol 1217 no 49pp 7807ndash7811 2010

[22] A Ali S S Somayeh and S Abbas ldquoSynthesis and anti-mycobacterial activity of 2-(phenylthio) benzoylarylhydra-zone derivatives servicesIranianrdquo Journal of PharmaceuticalResearch vol 10 no 4 pp 727ndash731 2011

[23] Z M Chen P Lu Y L Su and M He ldquoPreparation andperformance evaluation of water-based rust inhibitor for ironand steelrdquoMaterials Prodection vol 44 no 6 pp 58ndash59 2011

[24] T Jyothi and C AKe ldquoRasmuson Particle engineering ofbenzoic acid by spherical agglomerationrdquo European Journal ofPharmaceutical Sciences vol 45 no 5 pp 657ndash667 2012

[25] C G Silva and J L Faria ldquoPhotocatalytic oxidation of benzenederivatives in aqueous suspensions synergic effect induced bythe introduction of carbon nanotubes in a TiO

2matrixrdquoApplied

Catalysis B vol 101 no 1-2 pp 81ndash89 2010

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Applied ChemistryJournal of



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Analytical ChemistryInternational Journal of


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CatalystsJournal of


In this paper the photoelectrocatalytic performance ofbenzoic acid on TNA electrodes was investigated using athin-cell reactor The adsorption properties microcosmicdegradation process and reaction characterization of benzoicacid on TNAs were investigated by analyzing the change inthe photogenerated current-time (119868ph-119905) profilesThe result ofthis study provides a solid foundation for future research intothe reaction mechanism and reaction kinetics of aromaticorganic compounds on TNA electrode surfaces

2 Materials and Methods

21Materials Titanium sheets (025mm thick 999purity)were purchased from Sumitomo Chemical (Japan) Unlessotherwise indicated reagents were obtained from SinopharmChemical Reagent Company and were used as receivedHigh-purity deionised water was used in the preparation ofall solutions

22 Preparation of TiO2Nanotube Array Electrode The

preparing method of TiO2nanotube array electrodes has

been published in our previous work [18] Hence only keypoints of the fabrication process were summarized hereThe electrolyte contain 01molL NaF 1molL NaHSO

4and

02molL trisodium citrate also with NaOH added to adjustthe pH The TiO

2nanotube array electrodes are prepared

under constant stirring for 4 h After anodization the as-prepared sample was washed with high-purity deionizedwater and dried at room temperature Then it was annealedin a laboratory muffle furnace at 500∘C to crystallize inthe air ambience X-ray diffraction (Bruker D8 ADVANCEGermany) analysis showed that the crystal structure of TNAis anatase [18]

23 Apparatus and Methods All experiments were per-formed at room temperature in a three-electrode electro-chemical cell with a quartz window (082 cm2)The thicknessof the spacer was 01mm which defined the cell volume of82120583LThe structure of thin-cell reactor has been reported inour previous paper [18] The TiO

2nanotube array electrode

was used as a working electrode a saturated AgAgClelectrode and a platinum foil were used as the reference andthe counter electrodes respectively Also 2molLNaNO

3was

chosen as the supporting electrolyte in the experiment Thesupply bias and work current are controlled by a CHI (CHInstrument Inc CHI601d USA) electrochemical analyzer2W LED UV lamp (365 nm) was chosen as UV light sourceThe light intensity in experiment was measured by UV-Aultraviolet irradiator

3 Results and Discussion

31 The Photocurrent-Time Profile Property and Net ChargeDetermined in Thin-Cell In the photoelectrochemical reac-tion the oxidation of organic compounds at the electrodes

can be represented by the following electrode reaction equa-tion

C119910H119898O119895N119896X119902+ (2119910 minus 119895)H

2O

997888rarr 119910CO2+ 119902Xminus + 119896NH

3

+ (4119910 minus 2119895 + 119898 minus 3119896)H+

+ (4119910 minus 2119895 + 119898 minus 3119896 minus 119902) eminus

(1)

where X represents the halogen atom The numbers ofcarbon hydrogen oxygen nitrogen and halogen atoms inthe organic compound are represented by 119910119898 119895 119896 and 119902

Faradayrsquos law can be used to quantify the concentrationby measuring the charge passed if the organics is completelyoxidized That is

119876net = int 119868 119889119905 = 119899119865119881119862 (2)

where 119868 is the photocurrent from the oxidation of the organicsand 119905 is the time elapsed upon illumination 119876net is thedirect measure of net charge of the organics 119899 is the numberof electrons transferred and 119862 is the concentration of theorganics while the volume (V) and the Faraday constant (F)are known constants

Figure 1 shows a set of typical photocurrent-time profilesin the exhaustive mode in thin-cell at the fixed applied biaspotential of 25 V Figures 1(c) and 1(d) show the photocurrentresponse of a blank solution of 20molL NaNO

3and a

20molL NaNO3solution containing 04mmolL benzoic

acid in a thin-cell in the absence of illumination (electro-catalytic performances) The results show that there is nophotocurrent under dark conditions which indicate that thebenzoic acid in thin-cell cannot be oxidized Figure 1(a)shows the typical photocurrent response of a blank solu-tion of 20molL NaNO

3under the illumination conditions

(79mWcm2) The even photocurrent (119868blank) observed forthe blank solution originated from the stable oxidation ofwater Figure 1(b) shows the photocurrent response of a20molL NaNO

3solution containing 04mmolL benzoic

acid in a thin-cell under the same illumination (79mWcm2)The total photocurrent (119868total) observed for the benzoicacid solution was the total of two different componentsone originates from the photoelectrocatalytic oxidation ofbenzoic acid whereas the other was from water oxidationwhich was the same as 119868blank (Figure 1(a)) When the 119868totaldecreases to the level of 119868blank the oxidation of organics wasfinished Hence the processes of the photoelectrochemicalreaction in thin-cell were described by the change of I-tprofile

The net charge which originated from the oxidationof organics was defined as 119876net which can be obtainedby subtracting 119876blank from 119876total The net charge whichobtained by (2) was defined as 119879ℎ119876net Because the changeof net charge is directly related to concentration of organicsduring the photoelectrochemical reaction The degradationefficiency (DE) of the photoelectrochemical reaction can bedefined as the ratio of 119876net to 119879ℎ119876net which can be used indescribing the property of thin-cell


00004

00003

00002

00001

0

0 30 60 90 120119905 (s)

119868ph

(A)

ab

c

a b

c

d

d

119868total

119868blank








C7H6O2+ 12H

2O 997888rarr 7CO

2+ 30H+ + 30eminus (3)


119879ℎ119876net = 30119865119881119862 = 00237119862 (4)






00008

00006

00004

00002

0

minus00002

Curr

ent (

A)

0 1 2 3 4 5 6Potential (V)










00004

00003

00002

000010 40 80 120 160

Time (s)

Curr

ent (

A)


2 V15 V1 V









3concen-




00004

00005

00003

00002

00001

Curr

ent (

A)


553316158

0 30 60 90 120Time (s)



















02 119876net (mC) 0009423 0009434 0009421 0009467 0009449 0009409DE () 9947 9952 9938 9986 9967 9925

04 119876net (mC) 0009471 0009454 0009513 0009470 0009406 0009433DE () 9990 9972 10034 9989 9921 9950

08 119876net (mC) 0008552 0009075 0009434 0009445 0009466 0009429DE () 9021 9573 9952 9963 9985 9946

00006

00004

00002

0

Curr

ent (

A)



10502





119876net (mC) 0008112 0009260 0009415 0009436DE () 8557 9768 9931 9954





1198680ph =4 times 10


0

1 + 1061198620

+ 00003 1198772= 09945 (5)


00004

000036

000032

000028

119868ph

(A)

119905 (s)0 20 40 60 80 100



000034

000032

00003

0 01 02 03 041198620 (mmolL)

(a)

1198680p

h(A

)


0) and the net peak








4 Conclusions



Acknowledgments


References






2







2nanotube



2
















2











2during





2nan-







2matrixrdquoApplied











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


00004

00003

00002

00001

0

0 30 60 90 120119905 (s)

119868ph

(A)

ab

c

a b

c

d

d

119868total

119868blank








C7H6O2+ 12H

2O 997888rarr 7CO

2+ 30H+ + 30eminus (3)


119879ℎ119876net = 30119865119881119862 = 00237119862 (4)






00008

00006

00004

00002

0

minus00002

Curr

ent (

A)

0 1 2 3 4 5 6Potential (V)










00004

00003

00002

000010 40 80 120 160

Time (s)

Curr

ent (

A)


2 V15 V1 V









3concen-




00004

00005

00003

00002

00001

Curr

ent (

A)


553316158

0 30 60 90 120Time (s)



















02 119876net (mC) 0009423 0009434 0009421 0009467 0009449 0009409DE () 9947 9952 9938 9986 9967 9925

04 119876net (mC) 0009471 0009454 0009513 0009470 0009406 0009433DE () 9990 9972 10034 9989 9921 9950

08 119876net (mC) 0008552 0009075 0009434 0009445 0009466 0009429DE () 9021 9573 9952 9963 9985 9946

00006

00004

00002

0

Curr

ent (

A)



10502





119876net (mC) 0008112 0009260 0009415 0009436DE () 8557 9768 9931 9954





1198680ph =4 times 10


0

1 + 1061198620

+ 00003 1198772= 09945 (5)


00004

000036

000032

000028

119868ph

(A)

119905 (s)0 20 40 60 80 100



000034

000032

00003

0 01 02 03 041198620 (mmolL)

(a)

1198680p

h(A

)


0) and the net peak








4 Conclusions



Acknowledgments


References






2







2nanotube



2
















2











2during





2nan-







2matrixrdquoApplied











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


00004

00003

00002

000010 40 80 120 160

Time (s)

Curr

ent (

A)


2 V15 V1 V









3concen-




00004

00005

00003

00002

00001

Curr

ent (

A)


553316158

0 30 60 90 120Time (s)



















02 119876net (mC) 0009423 0009434 0009421 0009467 0009449 0009409DE () 9947 9952 9938 9986 9967 9925

04 119876net (mC) 0009471 0009454 0009513 0009470 0009406 0009433DE () 9990 9972 10034 9989 9921 9950

08 119876net (mC) 0008552 0009075 0009434 0009445 0009466 0009429DE () 9021 9573 9952 9963 9985 9946

00006

00004

00002

0

Curr

ent (

A)



10502





119876net (mC) 0008112 0009260 0009415 0009436DE () 8557 9768 9931 9954





1198680ph =4 times 10


0

1 + 1061198620

+ 00003 1198772= 09945 (5)


00004

000036

000032

000028

119868ph

(A)

119905 (s)0 20 40 60 80 100



000034

000032

00003

0 01 02 03 041198620 (mmolL)

(a)

1198680p

h(A

)


0) and the net peak








4 Conclusions



Acknowledgments


References






2







2nanotube



2
















2











2during





2nan-







2matrixrdquoApplied











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





02 119876net (mC) 0009423 0009434 0009421 0009467 0009449 0009409DE () 9947 9952 9938 9986 9967 9925

04 119876net (mC) 0009471 0009454 0009513 0009470 0009406 0009433DE () 9990 9972 10034 9989 9921 9950

08 119876net (mC) 0008552 0009075 0009434 0009445 0009466 0009429DE () 9021 9573 9952 9963 9985 9946

00006

00004

00002

0

Curr

ent (

A)



10502





119876net (mC) 0008112 0009260 0009415 0009436DE () 8557 9768 9931 9954





1198680ph =4 times 10


0

1 + 1061198620

+ 00003 1198772= 09945 (5)


00004

000036

000032

000028

119868ph

(A)

119905 (s)0 20 40 60 80 100



000034

000032

00003

0 01 02 03 041198620 (mmolL)

(a)

1198680p

h(A

)


0) and the net peak








4 Conclusions



Acknowledgments


References






2







2nanotube



2
















2











2during





2nan-







2matrixrdquoApplied











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




4 Conclusions



Acknowledgments


References






2







2nanotube



2
















2











2during





2nan-







2matrixrdquoApplied











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of









2during





2nan-







2matrixrdquoApplied











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

Documents

Research Article Photoelectrocatalytic Performance of ...downloads.hindawi.com/journals/ijp/2013/567426.pdf · To overcome these defects, considerable e ort has been ... It was also