Effect

,LnWenying(吕文英),LIXiaoxia(黎晓霞).,YULin(余ag),

    ;LIDaguang(李大光)

    ;“.DepartmentofResourceandEnvironment,FoshanUniversity,Foshan528000,China;2.FacultyofEnvironmentalScienceandEngineering,Guangzhou510006

    ;China;iFacultyofChemicalEngineeringandLightIndustry,GuangdongUniversityofTechnology,Guangzhou510006,China)

    ;Received27October2006;revised5January2007

    ;Abstract:Ho—dopedTi02nanoparticleswithhigherphotocatalyticactivitywerepreparedbyanacid—catalyzedsol—gelmethod.Thephoto—

    ;catalyticdecompositionofmethylorangeinaqueoussolutionwasusedasaprobereactiontoevaluatetheirphotocatalyticactivities.Theef- ;fectsofHodopingonthecrystallitesizes,crystalpattern,surfacecomposition,andopticalpropertyofthecatalystswereinvestigatedby

    ;meansoftechniquessuchasX—RayDiffraction(XRD1.TransmissionElect

    ronMicroscopy(TEM),DiffuseReflectanceUV—VisSpectros.

    ;copY(UV—visDRS).FourierTransformInfrared(Fr—IR),andPhoto—Lu

    miniscence(PL)spectra.Moreover,themodificationmechanismof ;Hodopingwasalsodiscussed.TheresultsshowedthatHod0pingcouldinhibit

    phasetransformationfromanatasetomtile,suppressthe ;growthofTiO,grains,causeblueshiftoftheabsorptionspectrumedge,acceleratesurfacehydroxylation,andenhancetheseparationeffi—

    ;ciencyofphotoinducedelectron.holepairs.whichresultedinasignificantimp

    dopedTiOz.Among rovementinthephotoreactivityofHo—

    ;them,theHo—dopedTiO,calcinedat500.Cachievedthehighestphotocatalyticactivity.

    ;Keywords:titaniumdioxide;Ho—doping;characterization;photocatalysis;methylorange;rareearths

    ;Photocatalyticdestructionoforganicpollutantsinthe ;presenceofTiO2appearstobeaviabledecontamination1Experimental ;processofwidespreadapplication,nomatterthestate(gas ;orliquid)orchemicalnatureoftheprocesstarget【lJ_How一

    1.1Preparationofrio.dopedTiO2catalysts

    ;Ver,t量ressnuadetect,me.I.02photocatalyncefficencYT ;opr印alreHodopedTiO2nanopartic1es,twokindsof

    ;lsnotgn.

    ;.

    ;asmerecomb1nationofphotogenemtedelec—

    ;solutions(solutionAandB)werepr印aredfirst.SolutionA

    ;n_no

    ;.

;1epairsresults1nlowphotoquaI1mme~ciencyH‟was

    ;madefrombutyltitanateandisopmpaI1o1inaI1appm一

    ;„here

    ;.

    ;fore,man

    ;.

    ;y

    ;.

    ;medsnaveeenundemnmproVepriateproportionanditspHwasaajustedtoabout3.0with

    ;cnehytlcacnot.riUd叩

    meanhHC1.SolutionBwasmadefromHo(NO3)3,whichwasdis.?nsm1 ;.

    ;2haveproVedbe

    ;.

    ;af1c1entmutetoaJterthesolvedwithdeionizedwater.Then,SolutionBwasadded

    ;photoacntyo.f！

    nan.osize,dnm‟Am?ngmen1press1.y.edropwiseintoSolutionAundervigomusstirring,andtheunmeIoIpublican0ns,nowever,t ;.

    ;ewreference

;,.

    ;sdeal,v1m

    ;molarratioofbutyltitanate,isopropaI1o1,deionizedwater,

    ;tne

    ;,

    ;srlhcespec仃umpropertyofnania,modifiedbYrare ;andHo3+was1:22:4:0.005.conseqI二ently,alightyellowish ;Inthepresentstudy,theHo—dopednaI1osizedTiO2:tl伽叻伽d竺

    dmn.gezedfo—rafew

    ;pho幻caJywerep印aredbya』

    1acd—cata1yedo‟gelge1wasagedforfivedaysunderobtuon,.

    ;aI1

    ;vl~

    ;d

    ;-

    ;thendried

    ;method.Withtheobjectivetounderstandtheeffectsof.,…….,,n

    二..:………！

    ;Ho.d:plng0nthephycoche衄浏properneS,pho幻

    gener.calcinedinairatdifferenttemperateventually

    ;1

    ;ated

;.

    ;argec

    ;,

    ;arriers,an

    ;.

    ;dsurfa

    ;.

    ;ceh

    ;.

    ;ydroxylofTi02

    ;.

    ;,thecata—Ho—do.edTiO2catalystsweree… ;d

    ;…

    ;ina---r

    ;„

    ;c

    ;ysspIeparedwerecharacenzedbymeansofVousspec—d

    ;opinglevelof0.5,abbreviatedas0.5%Ho—TiO2.Inthet

    ;ralanalysistechniques.Meanwhile,themodification…. ;.

    ;,,

;一…

    ;,

    ;…一

    ;mechanism.fHo-dopingwasa.discussedinthisarti.‟wasal

    ;B

    ;so

    ;F—oundationitem—:ProjectsupportedbytheNationa1Natura1ScienceFoundationofChina(20677012)

    ;,

    ;FoundadonofNaturalScienceofGuangd.ngPr0vince ;(04205301)andFoundationofScienceandTechnologyofGuangdongProvi

    nce(2006A36701003)

    ;Correspondingauthor:CAIHeshanfE.mail:caiheshanl5@yahoo.com.cn;T

    e1.:+86.757.82400596)

    ;一

    ;

    ;stitutedbydeionizedwater.Allthechemicalsusedinthe ;experimentswereofanalyticalgrade.

    ;1.2CharacterizationofH0.dopedTi02catalysts ;Thecrystallinephaseofthepreparedphoto—catalystswas

    ;analyzedbyXRD(RigakuD/MAX一2200vPC,Japan)with

    ;aCuKaradiation=0.154056nm)at36kVwithagraphJte

    ;monochromatorandscansat8o)/min.Thecrystallitesize ;couldbedeterminedfromthebroadeningofthecorre—

    rayspectralpeaksbytheScherrerformula,and ;spondingX—

    ;thelatticeparameterscouldalsobederivedfromtheXRD ;data.Theparticulatemorphologyofthephoto—catalystswas

    ;observedonTeM(JEM一100CXII.Japan)at190kV.Tbin—

    ;vestigatethechangesinthelocalstructureoftheTiO, ;photocatalysts.FT.spectraweremonitoredbytherlTlO ;nicolet380spectrometer(USA).UV—Visiblediffusereflec—

    ;tancespectraofthephotocatalystsweremeasuredona ;UV—Visspectrophotometer(uv一3150,Shimadazu,Japan)

    ;withareflectanceunit.Thephotoluminescence(PL1emis—

    ;sionspectraoftheTiO,samplesweremeasuredusingafluo—

    ;rescencespectrophotometerRF-5301,Shimadazu,Japan). ;1.3Measurementsofphotocatalyticactivityofphoto—

    ;catalysts

    ;Al1thephotocatalysisexperimentswereperformedonthe ;equipmentthathada250mlhollowcylindricalphotoreactor ;(SGY一1,NanjingSTOCo.Ltd.)equippedwithaquartzwa—

    ;terjacket.Theset—upisdisplayedinFig.1.A300W

    ;high--pressuremercurylampwithpfimarywavelengthdis-- ;tributionatapproximately365nmwaspositionedinthein—

    ;nerpartofthephotoreactorandcoolwatercirculated ;throughthequartzjacketsurroundingthelamp.Batchex—

    ;perimentswereconductedat(25?2).C.

    oxidation,theexperimentalsolutionwas ;Priortophoto—

    ;preparedasfollows:250mlmethylorangesolutionwitha ;concentrationof20mg/Lwaspipedintoabrownflask,and ;RefreshingwaterRefreshingwater

    ;Fig.1Schemeofphotoreactor

    ;JOURNALOFRAREEARTHS,VoL26,No.1.Feb.2008

    ;0.25gphotocatalystwasaddedintoitundershaking.inan ;ultrasonicator,for15min.Thesuspensionwastransferredto ;thephotoreactorandmagneticallystirredinadarkcondition. ;for30min,toestablishanabsorption/desorptionequilibrium ;condition.Theairwasaeratedtothesolutionatarateof200 ;ml/minandthenthefightwasturnedon.Theparallelali—

    ;quotsof10mlweretakenfromthesampleportatdifferent ;timeintervals,foranalysis,afterremovalofthecatalystby ;centrifugation,twice,at40OHDr/min.for10mineach.The ;absorblanceofresidualmethylorangewasdetectedbya ;UV—VissF》ectrometer(722N,Shanghai),andthedegradation ;rateofmethylorangewascalculated.

    ;2Resultsanddiscussion

;2.1XRDanalysis

    ;TheXRDpatternsofthephOtOcata1Vstsareshownin ;Fig.2.ItcanbeseenthattheXRDpattemsofpureTiO,and

    dopedTiO2nanoparticlescalcinedat500.Caresimilar, ;Ho—

    ;inwhichTiO,existsasasingleanatasephase.Although ;pureTiO2andHo—dopedTiO2samplescalcinedat650.C

    ;existasthecoexistenceofanataseandrutile.therelativein—

    ;tensityofthe110Deakdecreasesgreatlybecauseof

    doping.ItcanbededucedthatHo—dopinghasasignifi— ;Ho—

    ;cantinhibitoryeffectonthephasetransformationofTi02 ;andthenleadstohigherthermalstability.Physicalproper. ;tiesdeterminedfromXRDdatawiththeScherrerformulaof ;thesamplesarelistedinTab1e1.Itmayindicarethat ;Ho—dopingcouldalsohindertheincreaseofcrystallitesize ;duringcalcination.Infact.itseemsimpossibleforHo”to

    ;reallycooperatewiththematrixofTiO2becauseofthe ;mismatchoftheionicradiiofTiandHo”.Itisexpected

    ;thatthesurroundinglanthanideionswillinhibitthephase ;transitionofA—RthroughtheformationofaTi—O—Lnbond.

    ;Ontheotherhand,theLn20latticelockstheTi—Ospecies

    ;attheinterfacewithTiO,domains,preventingthenuclea- ;tionthatisnecessaryforthetransformationofanataseto

;20,f.)

    ;Fig.2XRDpatternsofpureTiO2andHo—dopedTiO2

    ;

    ;CAIHSetaL,EffectofHo.dopingonphotocatalyticacKvityofnanos~edTi02

    catalyst

    ;A:Anatase)R:Ruffle

    ;(a)

    ;O

    ;Fig.3TEMmicrographsofsamplespureTiO2(a)andHo—dopedTiO2(b)cal

    cinedat500.C

    ;mille,andresultsinthedecreaseofthecrystallitesizeof ;TiO2【7J.

    ;2.2TEManalysis

    ;Fig.3showstheTEMmicrographsofpureTiO2and ;Ho—dopedTiO2samplescalcinedat500.C.Theaverage ;particlesizeofpureTiO2rangesfrom15to20nm,whereas, ;thatofHo—dopedTiO2isaround10L_15nm.Incomparison ;withthepureTiO2sample,theHo—dopedonehasrelatively

    ;uniformsphericalgrains,narrowsizedistribution,andgood ;dispersivity,indicatingthatHo—dopingCanimprovethepar—

    ;ticlemorphology,andretardthegraingrowthofTi02on ;heat-treating.