Degradation of nitrobenzene using titania photocatalyst.docx

Degradation of nitrobenzene using titania photocatalyst.docx

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Degradationofnitrobenzeneusingtitaniaphotocatalyst

Degradationofnitrobenzeneusingtitaniaphotocatalystco

-dopedwithnitrogenandceriumundervisiblelightillumination

Xiang-ZhongShen

a,

Zhi-ChengLiua,Shan-MeiXieaandJunGuoa

aDepartmentofChemistryandMaterialsScience,HunanInstituteoftheHumanitiesandScienceandTechnology,Loudi417000,China

Received5March2008; 

revised1June2008; 

accepted3June2008. 

Availableonline8June2008.

Abstract

Atypeofnitrogenandcerium

co

-dopedtitaniaphotocatalyst,whichcoulddegradenitrobenzeneundervisiblelightirradiation,waspreparedbythesol–gelroute.Titaniumisopropoxide,ammoniumnitrate,andceriumnitratewereusedasthesourcesoftitanium,nitrogen,andcerium,respectively.X-raydiffraction（XRD）,X-rayphotoelectronspectroscopy（

XPS）

UV–visdiffusivereflectancespectroscopy（DRS）,scanningelectronmicroscopy（SEM）,andN2adsorption–desorptionisothermwereemployedtocharacterizetheas-preparedphotocatalyst.Thedegradationofnitrobenzeneundervisiblelightilluminationwastakenasprobereactiontoevaluatethephotoactivityofthe

co

-dopedphotocatalyst.ThecommercialTiO2photocatalyst（DegussaP25）,whichwasthoughtasahighactivephotocatalyst,waschosenasstandardphotocatalysttocontrastthephotoactivityofthenitrogenandcerium

co

-dopedtitaniaphotocatalyst.Theresultsshowedthatthephotocatalyticperformanceofthenitrogenandcerium

co

-dopedtitaniawasrelatedwiththecalcinationtemperatureandthecomponent.Thenitrogenatomswereincorporatedintothecrystaloftitaniaandcouldnarrowthebandgapenergy.ThedopingceriumatomsexistedintheformsofCe2O3anddispersedonthesurfaceofTiO2.Theimprovementofthephotocatalyticactivitywasascribedtothesynergisticeffectsofthenitrogenandcerium

co

-doping.

Keywords:

Nitrobenzenedegradation;Nitrogen;Cerium;

Co

-doped;Titaniaphotocatalysis

ArticleOutline

1.Introduction

2.Experimental

2.1.Photocatalystpreparation

2.2.Photocatalystcharacterization

2.3.Photocatalyticactivitytest

3.Resultsanddiscussion

3.1.XRDspectraofsamples

3.2.XPSspectraofthenitrogenandceriumco-dopedTiO2photocatalyst

3.3.UV–visDRSspectraofsamples

3.4.SEMphotographofN–Ceco-dopedTiO2photocatalyst

3.5.BETsurfacearea

3.6.Photocatalyticperformance

4.Conclusions

References

1.Introduction

Inthepastdecades,semiconductorphotocatalysishasbeenthefocusofnumerousstudiesandTiO2isfrequentlyusedasphotocatalysttodegradeagreatdealofpollutantsresultingfromindustrialandagriculturalwastesbecauseofitsexcellentproperties[1],[2],[3],[4]and[5].However,titaniacanbeactivatedonlybyultraviolet（UV）lightbecauseofthehighenergybandgap（ca.3.2 eVforanatase）[6]and[7].Inaddition,lowphotoquantumefficiencyandhighrecombinationofelectron–holepairsrestricttheapplicationoftitania[8],[9]and[10].Therefore,allkindsofattemptshavebeenmadetoimproveopticalabsorptionandphotocatalyticactivityforthepurposeofextendingthelightabsorptiontowardthevisiblelightrangeandtosuppresstherecombinationofhole–electronpairs,andthemostfeasiblemodificationmethodsseemtobedopingwithmetalanddopingwithnonmetal[9],[10],[11],[12],[13],[14]and[15].

Previousstudiesdemonstratedthatthemechanismsofmodificationtotitaniavariedwithmethods.Thedopingofnonmetalcouldnarrowthebandgapandmightdrivetheresponsetovisiblelightandcatalyticactivity,whereasthedopingofmetalcouldtraptemporarilythephotogeneratedchargecarriersandmightsuppresstherecombinationofphoto-inducedelectron–holepairswhenmigratingfromtheinsideofthephotocatalysttothesurface[6],[7],[9],[10],[13],[14],[15],[16],[17],[18]and[19].

Themodificationtotitaniaby

co

-dopingwasaneffectivemethodandthecooperateactionofthe

co

-dopingwasabletoimprovethephotocatalyticactivity.Yuanetal.[20]reportedthatthecooperativeactionof

co

-dopingofZn2+andFe3+overtitaniacouldobviouslyimprovethephotocatalyticperformanceforthephenoldegradation.Zhaoetal.[21]preparedtheB–Ni

co

-dopedphotocatalystusingthemodifiedsol–gelmethod.TheypointedoutthatincorporationofBintoTiO2couldextendthespectralresponsetothevisibleregionandthatNidopingcouldincreasegreatlythephotocatalyticactivity.Linetal.[22]preparedtheN–P

co

-dopedtitaniaphotocatalystextendingspectralresponsetothevisiblelightregion.Theyprovedthat

co

-dopingofbothNandPcouldimprovesignificantlythephotocatalyticactivityunderbothUVlightandvisiblelight.Baleketal.[23]reportedthatthenitrogenandfluorine

co

-dopedtitaniaphotocatalystshowinghighphotocatalyticactivityinavisibleregionofspectrumforacetaldehydedecompositionwaspreparedbyspraypyrolysisusingamixedsolutionofTiCl4andNH4F.Theydemonstratedthattheobservedhighphotocatalyticactivityofthesamplescouldbeascribedtoasynergeticeffectofnitrogenandfluorine

co

-doping.Lingetal.[24]preparedtheBandN

co

-dopedTiO2nanopowdersusingboricacidandammoniumfluorideastheprecursorsofboronandnitrogen.TheyprovedthatthesynergisticeffectofBandN

co

-dopingwasresponsibleforimprovingthephotocatalyticperformance.Thesereportsunequivocallyindicatedthatmodificationtotitaniaby

co

-dopingwasaneffectivemethodforincreasingthephotocatalyticactivity.

However,therewerefewreportsonthe

co

-dopedphotocatalystwithnitrogenandcerium.Inthepresentwork,thenitrogenandcerium

co

-dopedtitaniaphotocatalystwithhighphotocatalyticperformanceundervisiblelightwaspreparedusingthesol–gelmethod.ThepreparedsampleswerecharacterizedbyXRD,

XPS,

DRS,SEM,andN2adsorption–desorptionisotherm.Thephotocatalyticperformancewasevaluatedbymeansofthedegradationfornitrobenzeneundervisiblelightillumination.

2.Experimental

2.1.Photocatalystpreparation

Inthisstudytitaniumisopropoxidewaschemicallypureandotherswereanalyticallypure.Allchemicalswereusedwithoutanyfurtherpurification.Waterusedwasdeionizedwater.

Thenitrogenandcerium

co

-dopedtitaniawassynthesizedbythefollowingprocedure.Acertainamountofammoniumnitrateandceriumnitratewasdissolvedinthemixtureof10 mLofdeionizedwater,10 mLofglacialaceticacid,and80 mLofethanolatroomtemperaturetogainsolutionA.Titaniumisopropoxide（28.6 g,0.1 mol）wasdissolvedin100 mLofabsoluteethanoltoformsolutionB.Then,thesolutionBwasaddeddrop-wiseintothesolutionAwithin60 minundervigorousstirring,followedbystirringfor2 h.Theresultingsolwasagedfor48 hatroomtemperatureandwasdriedfor12 hat80 °C.Thus,thexerogelwastobeobtained.Theresultantxerogelwasmilledandannealedatdifferenttemperaturefor3 htoremovetheresidualorganiccompoundstopreparethenitrogenandcerium

co

-dopedphotocatalyst.ThesamplewaslabeledasN（x）Ce（y）TiO2-t,wherexandyrepresentedthemoleratiosofammoniumnitratetotitaniumisopropoxideandceriumnitratetotitaniumisopropoxide,respectively,andtdenotedthecorrespondingtemperatureofcalcination（°C）.

2.2.Photocatalystcharacterization

TheXRDpatternsofsampleswererecordedbymeansofaD/max-RBX-raydiffractometerequippedwithCuKαradiation（λ = 0.15406 nm）ina2θrangeof20–70°.Thescanningspeedwas4°/min.ThestandarddiffractionchartsofanataseandrutilewereusedtocomparewiththeobtainingXRDpatterns.CrystallitesizesofthesampleswereestimatedbytheScherrerequationandthelatticeconstantswerecalculatedusingfullprofilestructurerefinementofXRDdata.TheX-rayphotoelectronspectraofthe

co

-dopedphotocatalystweremeasuredbyaThermoEscalab250X-rayphotoelectronspectroscopeequippedwithAlKαexcitation.ThebindingenergiesforN1s,Ti2p,andCe3dwerecalibratedwithrespecttothesignalforadventitiouscarbon（bindingenergy = 284.6 eV）.Thesurfaceelectronicstatesandthechemicalstateswereanalyzedusingthebindingenergies.TheUV–visdiffusivereflectanceabsorptionspectraofsampleswererecordedonaShimadzu（Japan）UV–Vis2100Sspectrophotometerwithanintegratingsphereattachment.Thescanningrangewasbetween200 nmand800 nm.BaSO4wasusedasareference.Thestructuralmorphologyofsamplewasobservedbyamicroscope（PhilipsXL30CP）.TheparticlesizewasestimatedapproximatelybySEMphotograph.SpecificsurfaceareawasdeterminedbytheBETmethodbasedN2adsorptiononaAutosorb-1at77 K.Priortoadsorptionmeasurement,thesamplewasdegassedinanevacuationchamberfor12 hat423 K.

2.3.Photocatalyticactivitytest

Nitrobenzenewasusedasamodelorganicpollutant.Thedegradationofnitrobenzenewastakenasamodelreactiontoassessthephotocatalyticperformanceofthenitrogenandcerium

co

-dopedtitaniaphotocatalyst.Inallthestudies,thesuspensioncontaining200 mLof50 mg/Lnitrobenzeneaqueoussolutionand0.20 gofphotocatalystwasloadedina500 mLofhomemadequartzvesselbeakerandwasmagneticallystirred.A300 Wxenonlampprovidedthelightsourceanda400 nmglassfilterwasusedtoremovetheUVlight.Thedegradationreactionwascarriedoutundervisiblelightirradiationandthereactiontemperaturewasmaintainedat30.0 °C.Afterthemixturewasultrasonicatedfor10 minandstirredfor60 mininthedarktoachievetheadsorptionequilibrium,thexenonlampwasturnedon.Thedecompositionexperimentwascarriedoutfor4 h.Priortoirradiationandafteri