1---Coating Colloidal Carbon Spheres with CdS Nanoparticles Microwave-

CoatingColloidalCarbonSphereswithCdSNanoparticles:Microwave-AssistedSynthesisandEnhancedPhotocatalyticActivity

YongHu,*,†YuLiu,†HaishengQian,†ZhengquanLi,†andJiafuChen‡ZhejiangKeyLaboratoryforReactiveChemistryonSolidSurfacesandInstituteofPhysicalChemistry,ZhejiangNormalUniversity,Jinhua321004,P.R.China,and‡HefeiNationalLaboratoryforPhysicalSciencesatMicroscale,UniversityofScienceandTechnologyofChina,Anhui230026,P.R.ChinaReceivedAugust11,2010.RevisedManuscriptReceivedOctober10,2010ThismanuscriptdescribestheaccuratecoatingofCdSnanoparticlesonthesurfaceofcolloidalcarbonspheresbyafaciletwo-step,microwave-assistedmethodandthestudiesonthephotocatalyticactivityoftheC@CdScore-shellspheres.ForthecoatingofCdSnanoparticles,cadmiumionswereincorporatedintothehydrophilicshellofcolloidalcarbonspheresandreactedwithanintroducedsulfursourceunderamicrowavefieldtoobtaintheC@CdShybridspheres.Usingthisprocess,theas-preparedhybridstructurespreservedthegooddispersityanduniformityofinitialcarbonspheres,andthethicknessoftheCdSnanoparticlesshellcouldbevariedorcontrolledbytheirradiationtime.AphotoluminescencespectrumshowedthattheC@CdShybridspheresfeatureabroadgreenemissionataround494nm(λex=337nm).Additionally,CdSnanospheresweresuccessfullypreparedinaqueoussolutionviaamicrowave-assistedroute,andtheeffectofirradiationtimeontheproductswasalsoinvestigated.ThestudiesofthephotocatalyticpropertydemonstratethatthesefabricatedfunctionalhybridstructuresevincedahigherphotocatalyticdegradationactivitywhenexposedtovisiblelightirradiationthanthatofCdSnanospheresunderthesameconditions.†1.IntroductionItiswell-knownthatdyesareimportantorganicpollutants,andtheirreleaseaswastewaterintheecosystemisadramaticsourceofestheticpollutioninaquaticlife.1-3Mostofthedyesareresistanttobiodegradationanddirectphotolysis,andmanyN-containingdyessuchasrhodamineB(RhB)undergonaturalreductiveanaerobicdegradationtoyieldpotentiallycarcinogenicaromaticamines.Becauseofthecombinationofdifferentproper-tiesinoneparticle,whichmaybeconstructedofdifferentchemicalcomponents,core-shellorhybridnanostructureshaveattractedmuchinterestintheareaofapplication.4Cadmiumsulfide(CdS)isanimportantII-VIsemiconductorwithadirectbandgapenergyof2.42eV.5Itcanabsorbmostofthevisiblelightinthesolarspectrumandhaspotentialapplicationsinlaserlight-emittingdiodes,dye-sensitizedsolarcells,fluorescenceprobes,displays,photoelectrocatalysts,sensors,andoptoelectronicdevice,etc.6,7Becauseoftheiruniquephotochemicalandphoto-physicalproperties,CdSnanoparticlesasphotocatalystusedinthedegradationofdyesinwastewaterundervisiblelightirradia-tionhaveattractedintenseinterestinrecentyears.8,9Themecha-nismofCdSphotodegradationbehaviorcanbeexplainedasfollows.10(1)Horikoshi,S.;Hojo,F.;Hikaka,H.;Serpone,N.Environ.Sci.Technol.2004,38,2198.(2)Xu,Y.M.;Langfor,C.H.Langmuir2001,17,897.(3)Fu,H.B.;Pan,C.S.;Yao,W.Q.;Zhu,Y.F.J.Phys.Chem.B2005,109,22432.(4)Fang,C.L.;Qian,K.;Zhu,J.H.;Wang,S.B.;Lv,X.X.;Yu,S.B.Nanotechnology2008,19,125601.(5)Cao,J.;Sun,J.Z.;Hong,J.;Li,H.Y.;Chen,H.Z.;Wang,M.Adv.Mater.2004,16,84.(6)Bao,N.;Shen,L.;Takata,T.;Domen,K.;Gupta,A.;Yanagisawa,K.;Grimes,C.A.J.Phys.Chem.C2007,111,17527.(7)Morales,A.M.;Lieber,C.M.Science1998,279,208.(8)Lin,G.F.;Zheng,J.W;Xu,R.J.Phys.Chem.C2008,112,7363.(9)Jing,D.W.;Guo,L.J.J.Phys.Chem.B2006,110,11139.(10)Zhu,H.Y.;Jiang,R,;Xiao,L.;Chang,Y.H.;Guan,Y.J.;Li,X.D.;Zeng,G.M.J.Hazard.Mater.2009,169,933.First,CdSphotocatalystisevokedbyrelevantlighttoproduceelectrons(eq1).Second,theelectronsarescavengedbymolecularoxygen(O2)toyieldthesuperoxideradicalanion(O2•-)(eq2)andhydrogenperoxide(H2O2)(eq3)inoxygen-equilibratedmedia.CdSþhvfCdSðhþÞþe-e-þO2fO2•-e-þO2þ2HþfH2O2ð1Þð2Þð3ÞThesenewformedintermediateswillinterreacttoproducehydroxylradical3OH(eq4).*Correspondingauthor.E-mail:yonghu@zjnu.edu.cn.H2O2þO2•-f3OHþOH-þO2ð4ÞIntheend,the3OHradicalisapowerfuloxidizingagent,whichhasenoughcapacityfordegradingmostpollutants.However,CdSnanoparticlesareapttoaggregateinaqueoussolutionduringsynthesisprocesses,whichresultsinratherlowerphotodegradationefficiency.ThisobstaclecanbeovercomebyemployingCdSnanoparticlesloadingonthesurfaceofcolloidalcarbonspheresandobtainingobviouslyenhancedphotocatalyticactivity.Morerecently,agreatdealofresearcheffortshavebeendevotedtoexplorenovelstrategiesthatcanalterthephysicalpropertiesofcolloidalcarbonspheresbysurfacemodificationwithnoble-metalnanoparticles,oxidenanoparticles,orsemicon-ductorquantumdots.11-14Thesefunctionalcarbon-basedcom-positespheresdemonstrateeminentprospectsandopportunitiesfornewapplicationsinawidevarietyofareas.(11)Sun,X.M.;Li,Y.D.Angew.Chem.,Int.Ed.2004,43,597.(12)Li,H.;Wang,Q.;Shi,L.H.;Chen,L.Q.;Huang,X.J.Chem.Mater.2002,14,103.(13)Goutfer-Wurmser,F.;Konno,H.;Kaburagi,Y.;Oshida,K.;Inagaki,M.Synth.Met.2001,118,33.(14)Dennany,L.;Sherrell,P.;Chen,J.;Innis,P.C.;Wallace,G.G.;Minett,A.I.Phys.Chem.Chem.Phys.2010,12,4135.18570DOI:10.1021/la103191yPublishedonWeb10/29/2010Langmuir2010,26(23),18570–18575

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Scheme1.SchematicIllustrationoftheCoatingofCdSNanoparti-clesonColloidalCarbonSpheres

Thesurfaceofthecarbonspheresishydrophilicandhasadistributionof-OHandCdOgroups.11Upondispersalofthecarbonaceousmicrospheresinmetalsaltsolutions,thefunctionalgroupsinthesurfacelayercanbindmetalcationsthroughcoor-dinationorelectrostaticinteractions.Inaddition,therearesomenanosizedporesdistributeduniformlyonthesurfaceofcarbonspheres,whichmaybecausedbyremovalofresidualorganiccom-pounds,suchasoligosaccharidesfromthesurfacebywashingwithwaterandalcohol.11Theseporescouldnotonlyincreasethesurfacearea,butalsoaidpenetrationofreactivespecies.Aseriesofmetaloxidehollownanospheresusingcarbonaceousspheresastemplateshavebeensynthesizedviathissurface-layer-adsorptionandcalcinationroute.15,16Uptonow,thecoatingofcolloidalcarbonsphereswithCdSnanoparticleshasnotbeenreported.DistributingtheCdSnanoparticlesisaverygoodcandidaterouteforimprovingdegradationoforganiccompounds.Moreover,microwaveirradiationisanattractivemethodforthesynthesisofnanocrystalsandhastheadvantagesofshortreactiontime,small-21particlesize,narrowparticlesizedistribution,andhighpurity.17Herein,wereportasimplemicrowave-assistedmethodfortheaccuratecoatingofcolloidalcarbonsphereswithCdSnanoparticles.TheprincipleofthismethodisdescribedinScheme1.Inthefirststep,theadsorptionofcadmiumionincor-poratedintothehydrophilicshellofcolloidalcarbonspheresisconductedat60°Cfor12h.Then,theabovesamplesaredispersedin20mLofdistilledwaterand0.01molofNa2S2O3Wfor35H2Oandwereplacedinamicrowaverefluxingsystemat280differenttimes,resultinginC@CdScore-shellspheres.Thismicrowaveirradiationroutedemonstratesalow-temperature,environmen-tallysustainable,loadingofmetal-sulfideoncolloidalcarbonspheremethodology.Inaddition,thegreatestadvantageofthisrouteisthatCdSagglomerationcanbenaturallyavoided,becausethecationsarefirstabsorbedintothesurfacelayertoformacompositeshellandthenformsulfideviamicrowaveirra-diation,ratherthanformingaheterogeneouscoating.TheC@CdShybridspheresfeatureabroadgreenemissionataround494nm(λex=337nm)andexhibittheexcellentphotocatalyticactivitytowardthedecompositionofRhB.Inaddition,CdSnanospheresaresuccessfullypreparedinaqueoussolutionviathemicrowave-assistedroute,andtheeffectofirradiationtimeontheproductsisalsoinvestigated.ThesefabricatedfunctionalhybridstructuresevinceahigherphotocatalyticdegradationactivityexposuretovisiblelightirradiationthanthatofpureCdSnanospheresunderthesameconditions.(15)Sun,X.M.;Liu,J.F.;Li,Y.D.Chem.;Eur.J.2006,12,2039.(16)Qian,H.S.;Lin,G.F.;Zhang,Y.X.;Gunawan,P.;Xu,R.Nanotechnology2007,18,355602.(17)Wu,H.Q.;Wang,Q.Y.;Yao,Y.Z.;Qian,C.;Zhang,X.J.;Wei,X.W.J.Phys.Chem.C2008,112,16779.(18)Correa-Duarte,M.A.;Giersig,M.;Kotov,N.A.;Liz-Marzan,L.M.Langmuir1998,14,6430.(19)Qian,H.;F.;Qiu,X.;Li,L.;Ren,J.C.J.Phys.Chem.B2006,110,9034.(20)Raghuveer,M.S.;Agrawal,S.;Bishop,N.;Ramamath,G.Chem.Mater.2006,18,1390.(21)Mackenzie,K.;Dunens,O.;Harris,A.T.Sep.Purif.Technol.2009,66,209.Langmuir2010,26(23),18570–18575Article

2.MaterialsandMethods

Allreagentswereofanalyticalgrade,purchasedfromtheShanghaiChemicalReagentFactory,andusedasreceivedwith-outfurtherpurification.2.1.SynthesisofColloidalCarbonSpheres.Inatypicalprocedure,3.96gofglucosewasdissolvedin40mLofdistilledwaterformingaclearsolution.Thesolutionwastransferredintoa50mLautoclavewithaTeflonseal,maintainedat180°Cfor8h,andfinallyblackproductswereobtained.Theproductswerecollectedthroughcentrifugationat5000rpmfor20min,andthenbythreecyclesofcentrifugation-washing-redispersionwithdistilledwaterorethanol.Thefinalsamplesweredriedinanovenat80°Cformorethan6h.112.2.SynthesisofC@CdSCore-shellHybridSpheresviaMicrowaveIrradiation.Inatypicalprocedure,0.01molofCdCl232.5H2Owasaddedintoaround-bottomflaskanddis-solvedinasolventcontaining10mLofethanoland10mLofdistilledwater,whichformedaclearsolution.A25mgportionoftheas-preparedcarbonsphereswasaddedintotheabovesolutionandwaswelldispersedwiththeassistanceofsonicationfor10min.ThisCd-absorbedcarbonspheressolutionwasmaintainedat60°Cfor12htoarriveatthesaturatedextentofadsorptionandthenwascollectedbycentrifugation.Toremovepossiblesuper-fluouscationsandanions,theobtainedproductswerewashedwithethanolanddistilledwaterthreetimes,andthendriedat80°Cfor4h.Theabove-obtainedsamplesand0.01molofNaplacedinamicrowaverefluxingsystemirradiated2S2Oat335H2802OwereWfordifferenttimes,whichresultedincarbon@CdScore-shellcompositespheres.Aftercollectionbycentrifugation,thefinalproductswerewashedwithethanolanddistilledwaterthreetimesbeforedryingat80°Cfor4h.2.3.SynthesisofCdSNanospheres.Inatypicalprocedure,0.0025molofCdCl0.2gofpoly(vinylpyrrolidone)232.5H2O,0.005molofNa(PVP)weremixed2S2Owith335H302OandmLofdistilledwaterinaround-bottomflask.TheamountoftheNa2S2O335H2Owashighertoensurethecadmiumsaltreactioncompletely.Afterbeingvigorouslystirredfor5minatroomtem-perature,thesolutionwastransferredintoamicrowaverefluxingsystemandirradiatedat280Wfordifferenttimeintervals.Afterthereactionswerefinished,thefinalyellowprecipitateswerecol-lectedbycentrifugationandwashedwithethanolanddistilledwaterseveraltimesuntilhighpurityfinalproductswereobtained.Theseweredriedat60°Cundervacuum.2.4.Characterization.PowderX-raydiffraction(XRD)measurementsofthesampleswereperformedwithaPhilipsPW3040/60X-raydiffractometerusingCuKRradiationatascan-ningrateof0.06degs-1.Scanningelectronmicroscopy(SEM)wasperformedwithaHitachiS-4800scanningelectronmicro-analyzerwithanacceleratingvoltageof15kV.Transmissionelectronmicroscopy(TEM)wascarriedoutonaHitachiH-800transmissionelectronmicroscope.High-resolutiontransmissionelectronmicroscopy(HRTEM)andselectedareaelectrondiffrac-tion(SAED)wereconductedat200kVwithaJEM-2100Ffieldemissionmachine.EnergydispersiveX-rayspectrometry(EDS)wasperformedwithaspectroscopeattachedtoHRTEM,whichwasusedforelementalanalysis.SamplesforTEMmeasurementswerepreparedforTEMbydispersingtheproductsinethanolandplacingseveraldropsofthesuspensiononholeycarbonfilmssupportedbycoppergrids.FurtherevidenceforthecompositionoftheproductwasinferredfromX-rayphotoelectronspectros-copy(XPS),usinganESCALabMKIIX-rayphotoelectronspectrometerwithMgKaX-rayastheexcitationsource.ThephotoluminescencespectrawererecordedonanEdinburghFLSP920fluorescencespectrometer,andtheabsorptionspectraweremeasuredusingaPerkinElmerLambda900UV-visspectro-photometeratroomtemperature.Inaddition,forXRD,EDS,XPS,PL,andphotocatalysticactivitytests,wetooksamplesthatwereallobtainedviamicrowaveirradiationat280Wfor30min.DOI:10.1021/la103191y

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2.5.PhotocatalyticActivityofC@CdSHybridSpheresandCdSNanospheres.PhotocatalyticactivitiesofC@CdShybridspheresandCdSnanosphereswereevaluatedbythedegradationofRhBundervisiblelightirradiationofa500WXelampwitha420nmcutofffilter.Thereactioncellwasplacedinasealedblackboxwiththetopopened,andthecutofffilterwasplacedtoprovidevisible-lightirradiation.Inatypicalprocess,0.08gofas-preparedC@CdShybridspheresandCdSnano-spheresasphotocatalystswereaddedinto100mLofRhBsolution(concentration:3mg/L),respectively.Afterbeingdispersedinanultrasonicbathfor5min,thesolutionwasstirredfor2hinthedarktoreachadsorptionequilibriumbetweenthecatalystandthesolutionandthenwasexposedtovisiblelightirradiation.ThesampleswerecollectedbycentrifugationatgiventimeintervalstomeasuretheRhBdegradationconcentrationbyUV-visspec-troscopy.3.ResultsandDiscussionTheXRDpatternsofas-preparedC@CdShybridspheresandCdSnanospheresareshowninFigure1.FromXRDpatterns,thepositionofdiffractionpeaksofas-preparedC@CdShybridspheres(Figure1A)andCdSnanospheres(Figure1B)areingoodagreement,andthepeaksat2θvaluesof26.4°,43.9°,and51.9°correspondtothecrystalplanesofthe(111),(220),and(311)offace-centeredcubic(fcc)CdS(JCPDSstandardcardno.,respectively.No89-0440)withacellconstantofa=5.811Aotherimpurityphasesweredetectedinanyoftheseproducts.TheXRDpatternsofas-preparedC@CdShybridspheresandCdSnanospheresarebothobtainedaftermicrowaveirradiationfor30min.TheaveragesizeofCdSnanoparticlescalculatedusingtheDebye-Scherrerequationbasedonthefullwidthathalf-maximumofthediffractionpeakwere6.0and3.5nm,respec-tively.Wethinktheexistenceofsurfactant(PVP)intheprepara-tionofCdSnanospheresisthekeyfactortoobtainlesscrystallineCdS,whichcouldpreventCdScrystallitesreunitingtogetherandformingclustersatrandom.Eventhoughtheirradiationtimeisthesame,theC@CdShybridspheresshouldgivesharperandhigherintensitypeaksthanCdSnanospheresintheXRDpattern.Inaddition,theXRDpatternsofas-preparedC@CdShybridsphereswithdifferentirradiationtimeareshowninSupportingInformation,FigureS1.TheaveragesizeofCdSnanoparticleswithirradiationtime(5,10,30min),calculatedusingtheDebye-Scherrerequationbasedonthefullwidthathalf-maximumofthediffractionpeak,was1.6,3.8,and6.0nm,respectively.Thus,thesizeofCdSnanoparticlesisgraduallyincreasedastheirradiationtimegoeson.ThetypicalSEMimageofnearlymonodispersecarbonspheresandtheas-preparedC@CdShybridspheresobtainedbyFigure1.XRDpatternsof(A)theC@CdShybridspheresand(B)CdSnanospheres.Figure2.TEMimageoftheas-preparedC@CdShybridspherespreparedbymicrowaveirradiationat280Wfor(A)5minandHRTEMimage(inset),(B)10minandHRTEMimage(inset),(C)30minandSAEDpattern(inset),and(D)EDSpatternoftheshellofC@CdShybridspheres.18572DOI:10.1021/la103191yLangmuir2010,26(23),18570–18575

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Figure3.TypicalSEMimagesofas-preparedCdSnanospheresobtainedviamicrowaveirradiationfordifferenttimes:(A)10,(B)20,(C)30,and(D)50min.Figure5.PLspectraof(A)C@CdShybridspheresand(B)CdSnanospheres(λex=337nm).Figure4.TypicalTEMimagesofas-preparedCdSnanospheresobtainedviamicrowaveirradiationfordifferenttimes:(A)10,(B)20,(C)30,and(D)50min.microwaveirradiationfordifferenttimesareshownintheSupport-ingInformation(FigureS2).TofurtherinvestigatethegrowthprocessforthecoatingofcolloidalcarbonsphereswithCdSnano-particles,wemonitoredthesamplesbyTEMwithdifferentmicrowaveirradiationtimes.TypicalTEMandHRTEM(inset)imagesofas-preparedC@CdShybridsphereswereshowninFigure2.AsseeninFigure2A-C,withthemicrowaveirradiationpowerkeptat280Wandtheirradiationtimeenhancedto5,10,Langmuir2010,26(23),18570–18575

and30min,thethicknessesofCdSnanoparticleshelllayersofthefinalproductswere10,20,and50nm,respectively.Fromtheseimages,itcanbeseenthattheas-preparedhybridstructurespre-servedthegooddispersityanduniformityofinitialcarbonspheres.BecausetheprecursorwasthesaturatedCd-absorbedcarbonspheresandtheonlysulfursourcewasprovidedintheprocessofmicrowaveirradiation,noobviouschangeofthethick-nessofshellwasobservedafter30min.TheSAEDpattern(insetinFigure2C)demonstratedthedetailsofthelocalpolycrystallinestructure,andtheconcentricringscouldbeassignedasdiffrac-tionsfromthe(111),(220),and(311)planesoffccCdS,whichwasconsistentwiththeXRDresult.TheEDSpatternofsurfacelayerofas-preparedC@CdShybridspheresisshowninFigure2D,whichconfirmstheexistenceofCdSnanoparticlesonthecarbonspheres.Itisobviousthatthecopperpeakiscausedbythecoppergridusedtoclampthesamples.ThecompositionoftheproductsisfurtheranalyzedbyXPS,andthetypicalsurveyspectrumoftheC@CdShybridspheresisshownintheSupportingInformation(FigureS3).Figure3andFigure4showtypicalSEMandTEMimagesoftheas-preparedCdSnanospheresobtainedviathemicrowaveirradiationrouteat280Wfordifferenttimes.Fromthefigures,itisclearthatCdSnanospheresarerandomlyandhomogeneouslydistributedinallareas.Bychangingmicrowaveirradiationtime,wetrytogetbetterexperimentalconditionsforthecontrolofDOI:10.1021/la103191y

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Figure6.TheabsorptionspectraoftheRhBsolutionatdifferentexposuretimeinthepresenceof(A)C@CdShybridspheresand(B)CdSnanospheres.(C)TherelationshipofdegradationrateofRhBwiththeirradiationtimeand(D)thedegradationrateofRhBusingdifferentbatchesofC@CdShybridspheresasphotocatalystsafterexposuretovisiblelightirradiationfor40min.uniform-sizedandmonodisperseCdSnanospheres.Figure3panelsA-Dshowexperimentalresultscarriedoutwithdifferentmicro-waveradiationtimes.Theirradiationtimewascontrolledfor10,20,30,and50minandthecorrespondingaveragediameterofthenanosphereswas80,100,120,and150nm,respectively.Thelongertheirradiationtimewas,thelargerwasthesizeofCdSnano-spheresformed.Itisclearlyshownthattheuniformityofthenanospheresisbetterwhentheradiationtimeis30min.TheTEMresultsareingoodagreementwiththatoftheSEM.ComparedtothereactionintheabsenceofPVP,themicrowavereactioninthepresenceofPVPcanbewellcontrolledandproducesamoreuniformformationofCdSnanospheres.ItisthoughtthatthefunctionofPVPhereistopreventCdScrystallitesreunitingtogetherandformingclustersatrandom.22Toinvestigatetheopticalpropertiesoftheas-preparedC@CdShybridstructuresandtheirpotentialapplicationasphotonicmaterials,astudyoftheirPLspectrumwasrecordedatroomtem-perature.Foracomparison,theopticalpropertiesofCdSnano-sphereswerealsostudiedatthesameconditions.Figure5showsthePLspectraoftheas-preparedC@CdShybridspheresandCdSnanospheres.TheC@CdShybridstructures(Figure5A)andCdSnanospheres(Figure5B)allfeatureabroadgreenemissionataround494nmunderanexcitationwavelengthof337nm.ThereisnovariationintheanalysisofPLspectraofthebandgapenergyofCdSwhentheCdSwerecoatedonthesurfaceofcolloidalcarbonspheres.ThePLpeakintensityfortheC@CdShybridspheresismuchstrongerthanthatfortheCdSnanospheres.ThismaybeattributedtotheweakPLinthewidewavelengthregionofcarbonaceousspheres.ThePLinamorphouscarbonisthoughttooccurduetotheradiativerecombinationofelectronsandholesintheband-tailstatescreatedbysp2richclusters.23,24Thus,thePL(22)Wang,Z.X.;Chen,J.F.;Xue,X.;Hu,Y.Mater.Res.Bull.2007,42,2211.(23)DeMichelis,F.;Schreiter,S.;Tagliaferro,A.Phys.Rev.B1995,51,2143.(24)Henley,S.J.;Carey,J.D.;Silva,S.R.P.Appl.Phys.Lett.2004,85,6236.ofas-preparedC@CdShybridspheresshowsahigherbaselinethanthatofpureCdSnanospheres.Figure6A,BdisplaysthephotodegradationbehaviorsofRhBcatalyzedbyC@CdShybridspheres(sample1)andCdSnano-spheresundervisiblelightillumination,respectively.Theabsorp-tionpeaksat553nmcorrespondingtoRhBdiminishedgraduallywithanabsorptionbandshifttoshorterwavelengthsastheexpo-suretimeisadded;similarresulthavealsobeenreportedbyWuetal.25Toinvestigatetherelationshipofthesample’smorphologyandthephotocatalyticefficiency,thedependenceofthedegrada-tionrateofRhBontheirradiationtimeusingdifferentsamplesisplottedinFigure6C.ThecompletephotodegradationofRhBinthepresenceofpureCdSnanospheresrequirs90min,butthatofC@CdShybridspheresonlyrequires40min,indicatingtheenhancedphotocatalyticactivityofthehybridstructuresamples.Thestabilityofaphotocatalystisimportanttoitsapplication.Tofurtherdemonstratethereproducibilityofphotocatalyticactiv-itybetweendifferentbatchesofC@CdS,thephotodegradationbehaviorsofRhBcatalyzedbyothersamples(2,3,4,5,and6),whichwereallobtainedviamicrowaveirradiationfor30minarecarriedout.Figure6DshowsthedecolorizationratesusingdifferentbatchesofC@CdShybridspheresasphotocatalystsare97.8%,94.3%,95.5%,87.2%,91.7%and94.9%,afterexposuretovisiblelightirradiationfor40min.Theresultsshowthatthephoto-catalyticactivityofC@CdShybridsphereshasgoodstability.Thesuperiorphotocatalyticperformanceofthesehybridstruc-turesmaybeascribedtothefollowing.First,thesurfacesensitizerofcarbonaceousspecieswasconsideredtobetheoriginofitsvisiblelightphotocatalyticactivity.26Second,thehydroxylgroupsofcarbonspheresurfacesmayacceptphotogeneratedholestopreventelectron-holerecombination.27Theseparationofphotogenerated(25)Wu,J.;Duan,F.;Zheng,Y.;Xie,Y.J.Phys.Chem.C2007,111,12866.(26)Zabek,P.;Eberl,J.;Kisch,H.Photochem.Photobiol.Sci.2009,8,264.(27)Sato,S.Langmuir1988,4,1156.18574DOI:10.1021/la103191yLangmuir2010,26(23),18570–18575

Huetal.electron-holescansignificantlybefacilitatedinthepresenceofcarbon.Inaddition,thepollutantsRhBareadsorbedonadsor-bentsupports(carbonaceousspheres),resultinginahigherpollu-tantenvironmentaroundtheloadedCdSnanoparticles.Thus,theC@CdSevincedahigherphotocatalyticactivity.Thephotoca-talyticpropertiesofthesefabricatedfunctionalhybridstructuresisverycomplicated.Wewillfurtherdoaseriesofexperimentscenter-ingontheinfluenceofthedifferentbatchesofC@CdSonpho-tocatalyticactivityanddoextendedresearchonthedegradationmechanisminfluencedbytheinterfaceofcarbonandCdS.Wewillreportthisworkinthefuture.4.ConclusionsWedemonstratedafaciletwo-step,microwave-assistedmeth-odfortheaccuratecoatingofCdSnanoparticlesonthesurfaceofcolloidalcarbonspheres.First,theadsorptionofcadmiumionwasincorporatedintothehydrophilicshellofcolloidalcarbonspheres,conductedat60°Cfor12h,andthenwashed,centrifuged,dried,andcollected.Second,theabovesamplesweredispersedinto20mLofthedistilledwaterandthen0.01molofsulfursourcewasadded.Themixturewasplacedinamicrowaverefluxingsystemat280Wfordifferenttimes,resultinginC@CdShybridspheres.Withthismethod,theas-preparedhybridstructurespreservedthegooddispersityanduniformityoftheinitialcarbonspheres,andLangmuir2010,26(23),18570–18575Article

thethicknessoftheCdSnanoparticlesshellcouldbevariedorcontrolledbytheirradiationtime.Inaddition,CdSnanospheresweresuccessfullypreparedinaqueoussolutionviaamicrowave-assistedroute,andtheeffectofirradiationtimeontheproductswasalsoinvestigated.ThefabricatedfunctionalC@CdShybridstructuresevincedahigherphotocatalyticactivityinthedegrada-tionofRhBthanthatofpureCdSnanospheresunderthesameconditions.Itisexpectedthatthiskindofhybridstructuresshouldbeidealphotocatalystsintheremovalofdyesandotherorganicpollutants,andfurthercouldbeexploitedforapplicationsinpho-tocatalyticcleaners,optoelectronicdevices,waterpurification,envi-ronmentalcleaning,andsolarenergyconversion.Acknowledgment.FinancialsupportfromtheEducationalCommissionofZhejiangProvinceofChina(Z200909406),Zhe-jiangQianjiangTalentProject(2010R10025),andtheNationalNaturalScienceFoundationofChina(20806075,20901068)isgratefullyacknowledged.SupportingInformationAvailable:TheXRDpatterns,SEMimages,andXPSspectraofas-preparedC@CdSviamicrowaveirradiationfordifferenttimes.ThismaterialisavailablefreeofchargeviatheInternetathttp://pubs.acs.org.

DOI:10.1021/la103191y18575