纳米氧化锌的控制制备及其光催化性能的研究

华中科技大学博士学位论文纳米氧化锌的控制制备及其光催化性能的研究姓名：王辉虎申请学位级别：博士专业：材料学指导教师：谢长生20060928IZnOZnOZnOZnOZnOZnOZnOZnOZnOZnOZnOZnOZnO1CH3OHZn(CH3COO)2.2H2OZnOFESEMXXRD21512ZnOZnO2(CH2)6N4HMTAZnOZnOFESEMTEMXRDZnOHMTA3(Zn(NO3)2.6H2O)HMTAFESEMXRD-TG-DSC250ZnOZnO1-ZnOIIZnO2ZnOXXPSZnO700-800Pa2200-2300Pa1500-1900PaZnO3ZnOTEM-UV-VisFT-IRZnO10nmZnO-ZnO(50nm)ZnOFESEMXRD300500800ZnO0.05mol/LZnO500ZnO3h5h7hZnOZnOIIIAbstractIthasbeendemonstratedthatthepropertiesofnanometer-sizedZnOwererelatedtoitssurfacecharacteristicsclosely,suchassize,shape,deficiencyandsoon.Thus,totailorZnOwithnovelelectrical,opticalandchemicalproperties,thegrowthofnanometer-sizedZnOshouldbecontrolledwell.Atthesametime,theapplicationofnanometer-sizedZnOinthetreatmentandprotectionofenvironmentalpollutionhasbeenattractedthepublicconcernforsemiconductor-assistedphotocatalysiscanconvertthepollutantsintoharmlesssubstancesdirectly.ZnOisoneofthemostwidelyusedeffectivephotocatalystforitshighefficiency,non-toxicnatureandlowcost.Inthispaper,firstly,severalpreparationmethodsofnanometer-sizedZnOwereintroducedinbrief.Themicrocosmicmechanismsofthenanometer-sizedZnOphotodegradationandthefactorsthatcanaffectthecatalysisefficiencywerediscussedindetailaswellasthemethodsthatcanimprovetheefficiencysofar.Subsequently,thecontrolledsynthesismethodsofnanometer-sizedZnOanditsphotocatalyticperformancehavebeenstudiedindetail.Inthechapter2,severalkindsofZnOnanostructurewithspecialmorphologiesandstructureshavebeenfabricatedthroughthelowtemperaturesolutionroute.Thekeyfactorsinthesynthesisprocesshavebeenfoundanddiscussed.1)Inthemethanolsolvent(CH3OH),thehydrolysisofzincacetatedihydrate(Zn(CH3COO)2.2H2O)wascontrolledwellthroughaddingH2OtoobtainZnOwithdifferentmorphologies.Theresultsoffieldemissionscanningelectronmicroscopy(FESEM)andX-raydiffraction(XRD)showedthemorphologytransitionprocessofZnOfromirregularshapetoregularcone-like,tostandardhexagonalplatewiththeincreasingvolumeratioofH2Otomethanolsolventfrom2:15to1:2,whichdemonstratedtheroleofH2OontailoringthemorphologyofZnO.2)Inthissection,thenovelZnOmicrospheresweresynthesizedbythecomplexsysteminwhichstartingreagents,Zn(CH3COO)2,H2O,andhexamethylenetetramine((CH2)6N4,HMTA),werekeptinmethanolsolutionat60for12h.TheFESEM,transmissionelectronmicroscopy(TEM)imagesandXRDpatternresultsshowedthatthemicrosphereswereformedbyZnOnanoplatesthataligninaregularperiodicityviaself-assembly.TheIVformationprocessofthisnovelnanostructurewasaslowandcomplicatedoneandthechemicalreagentHMTAwasthekeyfactor.3)Inthesolutionwithdistilledwaterassolventandzincnitratehexahydrate(Zn(NO3)2.6H2O),HMTAasreactants,anovelmicrospherewithnanometerholesseparatedbythinflakesandZnObranchrodlikestructureandakindofthinsolidfilmwereformedafter24hat60.Throughcontrollingthedepositiontimeandtheconcentrationofsolution,thepureporousthinsolidfilmscanbeprepared.Whenthecitricacidascappingmoleculeswasaddedintothesolution,theprecipitateswerethepuremicrospheres.Asacontrast,thepureZnObranchstructurewasobtainedthroughchangingthesolventfromH2Otomethanol.TheresultsofFESEM,XRDandthermogravimetry-differentialscanningcalorimetry(TG-DSC)showedthatafterannealingat250for1h,thethinflakesofnovelmicrosphereshavebeentornoffandconsistedofthesmallZnOnanoparticleswiththeaveragesize10nm.However,theporoussurfaceofmicrosphereswasmaintained.Inthechapter3,therelationbetweenthesurfacecharacteristicsofZnOnanoparticlesandthephotocatalyticperformancewasstudied.1)Throughtheevaporation-condensationmethod,ZnOnanoparticleswiththreedifferentmorphologiesincludingirregular,tetrapodandplatewerepreparedbycontrollingtheevaporationtemperatureataconstantoxygenpartialpressure2000Pa.ThephotodegradationefficiencyofMethylOrangeshowedthattheeffectofmorphologyonthephotoactivityofZnOnanoparticlescanbeascribedtothesurfaceareaandthecompositionofsurfacecrystalplanes;2)ZnOnanoparticleswithdifferentamountsofoxygendeficiencywerepreparedthroughcontrollingtheoxygenpartialpressureataconstantevaporationtemperature.TheX-rayphotoelectronspectroscopy(XPS)resultsdemonstratedtheamountofsurfaceoxygendeficiencyaswellasthechemisorbedoxygendecreasedwiththeincreaseofoxygenpartialpressurefrom700-800Pato2200-2300Pa.However,ZnOnanoparticlesthatpreparedat1500-1900PadisplayedthehighestphotoactivitybydecomposingMethylOrange,whichshowedtheappropriateamountofoxygendeficiencywasbeneficialtotheseparationofphotoinducedcarriers;3)ZnOnanoparticleswerepreparedbychemicaldepositionmethod.Itssize,morphology,surfacecharacteristicwaspresentedusingdifferenttestingtechniquessuchasTEM,Ultraviolet-visible(UV-Vis)absorptionspectrumandFouriertransform-infraredVspectrometry(FT-IR).ThesizeofZnOnanoparticleswas10nm,whichshowedthequantumsizeeffect.However,itssurfacewassurroundedbyorganicsubstances(acetateion).Theresultsofphotodegradationshowedthattheacetateionssuppressedthetransferofphotoinducedcarriers,whichresultedinthelowerphotoactivityofZnOnanoparticlesthantheZnO(50nm)nanoparticlespreparedbyevaporation-condensation.Inthechapter4,theZnOsolidfilmswerefabricatedthroughtheliquiddepositionmethod.There