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