氧化铈纳米粒子的制备.ppt

Members:XianhongRuiYuChenLitaoYanHuaminYaoLiangjunYi,Synthesisofcerianano-particles,DepartmentofMaterialsScienceandEngineeringUniversityofScienceandTechnologyofChinaJan3,2008,SimplyintroducethestructureandapplicationsofCeO2,3.Futureworks,2.SynthesisofnanocrystallineCeO2bydifferentmethods,Outline,Briefintroduction,CeO2属于萤石型氧化物。CeO2晶胞中的Ce4+按面心立方点阵排列，O2-占据所有的四面体位置，每个Ce4+被8个O2-包围，而每个O2-则与4个Ce4+配位。,1.StructureofCeO2,2.功能特性,CeO2的结构中有1/2立方体空隙，可称之为敞型结构。敞型结构允许离子快速扩散。经高温(T950)还原后，CeO2转化为具有氧空位、非化学计量比的CeO2-X氧化物(0x0.5)，而在低温下(T450)CeO2可形成一系列组成各异的化合物。值得注意的是，即使从晶格上失去相当数量的氧，形成大量氧空位之后，CeO2仍然能保持萤石型晶体结构，这种亚稳氧化物暴露于氧化环境时又易被氧化为CeO2，因而CeO2具有优越的储存和释放氧功能及氧化还原反应能力，同时CeO2也有着良好的化学稳定性和高温快速氧空位扩散能力。,ApplicationsofCeO2,此外，CeO2还用作催化材料、高温氧敏材料、pH传感材料、电化学池中膜反应器材料、燃料电池的中间材料、中温固体氧化物燃料电池(SOFC)用电极材料,SynthesisofCeO2,1.Directprecipitation,Nitrate:Ce(NO3)3or(NH4)2Ce(NO3)6,Precipitant:ammoniaorNH4HCO3,Surfaceactiveagent:PEG-4000,Process:nitrateandPEG-4000weredissolvedindistilledwate.ThenammoniaorNH4HCO3solutionwasaddeddropwiseundervigorousstirringtillthepHreached9.Theprecipitatewasfiltered,washedthricewithdistilledwaterandalcoholanddriedat80overnight.,Resultsanddiscussion,SEMphotoesofprecursor,XRDofprecursor,(a):Ce(NO3)3+NH3H2O(b):(NH4)2Ce(NO3)6+NH3H2O(c):Ce(NO3)3+NH4HCO3(d):(NH4)2Ce(NO3)6+NH4HCO3,Microwavehomogeneousprecipitation,Microwavereactionequipment,Nitrate:Ce(NO3)3or(NH4)2Ce(NO3)6,Precipitant:urea,Surfaceactiveagent:PEG-4000,CO(NH2)2+H2OCO2+2NH3NH3+H2ONH4+OH-CO2+H2OCO32-+2H+,水解生成的构晶离子OH-、CO32-,在微波辐照作用下,与Ce3+、Ce4+等结合生成不溶前驱物,Resultsanddiscussion,XRDofprecursor(a),(a)Ce(NO3)3+urea,withoutPEG-4000(b)Ce(NO3)3+urea+PEG-4000(c)(NH4)2Ce(NO3)6+urea+PEG-4000,SEMphotoofCeO2calcinedat600,SEMphotoofprecursor(a),HydrothermalsynthesisofCeO2nano-particles,1.Cerium(IV)hydroxideprecursor,A.I.Y.Tok,etal(NanyangTechnologicalUniversity),JournalofMaterialsProcessingTechnology190(2007)217222,2.Ceriaacetateprecursor,Fig.1.DTA/TGofCe(OH)4precursor,Resultsanddiscussion,Thetotalmeasuredweightlossfrom25to900was11.64%,whilethetheoreticalweightlossforthedecompositionofceriumhydrateoxideis17.3%,i.e.Ce(OH)4/CeO22H2OtoCeO2,ThedecompositionoftheprecursorisaformofdehydrationprocessofthehydratedCeO2,thedifferenceinweightlossobservedcouldbeduetothefollowingreasons:(a)precipitateconsistingofapartiallyhydratedformofceria,(i.e.CeO2xH2O),forwhicha11.64%weightlossondecompositioncorrespondstox=1.35or(b)theprecipitateconsistedofamixtureofphaseslikeCeO22H2O+CeO2,Fig.2DTA/TGofceriaacetateprecursor,Theprecursormeasuredatotalweightlossof12.55%withfourdistincttemperaturepeaks,Thefirstendothermicpeakwasdetectedataround100.Thisisattributedtothereleaseofthewatermoleculespresentintheprecursor,From100to200,theweightlosswasattributetotheremovalofthesurfaceacetategroupsandlatertheformationoftheaceticacidwhensurfaceacetatehydrolysisoccurs.Thisalsoexplainstheveryweakendothermicpeakdetectedat200,Therewasasharpweightlossfrom200to400andacorrespondingexothermicpeak.Thisexothermicpeaksuggeststheformationofoxyacetateanddioxocarbonatecomplexeswithcerium,Ce(OH)(CH3COO)andCe2O2CO3,Astemperatureincreasedto700,theCe2O2CO3decomposedendothermallytoproducethefinalproductCeO2,Fig.3DTA/TGforCeO2synthesizedfromceriaacetate:(a)after6htreatment;(b)after24htreatment,after6and24hofhydrothermaltreatment,weightlossisdramaticallyreducedto2.64and1.37%,Thedistincttemperaturepeaksaresimilartothatoftheprecursor.However,thedistinctexothermicpeakforthehydrothermaltreatedsamplesisnolongeraspronouncedasthatoftheprecursor,Thiscouldbeduetotheamountofacetatecomplexesformationbeingreducedconsiderablyafterhydrothermaltreatment.Tracesofceriumacetatecomplexeswerestillpresentinthesamplesafterhydrothermaltreatment.Theamountishowever,significantlylowerthanthatfoundintheprecursor,Fig.4CeO2usingCe(OH)4precursor(250)asafunctionoftime,Fig.5CeO2usingceriaacetateprecursor(250)asafunctionoftime,Fig.4,thenano-particlesexhibitedsomedegreeofcrystallinityanddisplayedallofthemajorpeaksofCeO2withacubicstructureafter6htreatment,Nosignificantimprovementincrystallinitywasobservedbetween6and24h,andthepeakswerebroadwithweakintensities.Thistrendissimilarwiththeceriaacetatesystem,Fig.5,thepeaksaresignificantlynarrowerwithhigherintensitiessuggestinglargercrystallitesizesatanaverageof15.5nmascalculatedandlargerdegreeofcrystallinityascomparedtothecerium(IV)hydroxidesystem.Thepeaksathigher2anglescanalsobeclearlyobservedforallsamples,Fig.6.LatticeconstantofCeO2afterhydrothermaltreatmentat250usingCe(OH)4precursor,Fig.7LatticeconstantofCeO2afterhydrothermaltreatmentat250usingceriaacetateprecursor,thelatticeparameterdecreasedbyabout0.2%afterhydrothermaltreatmentat250for6h.From6to12hatthesametemperature,thelatticeexpanded.Thelatticeconstantonlyvariedwithinanarrowrange(|a|/a0.03%)after12h,indicatingthatthestructurebecamestable.,Thelatticeconstantdecreasedbyabout0.5%afterhydrothermaltreatmentat250Cfor6h.Furtherchangesoflatticeconstantwereverysmallwhentreatmentdurationwasincreased.Thevariationoflatticeconstantwaslessthan0.03%,Fig.8CeO2fromCe(OH)4(24h)heattreatedat(a)500,(b)1000,Fig.9CeO2fromceriaacetate(24h)heattreatedat(a)500,(b)1000,Inbothfigures,itcanbeseenthatthecharacteristicpeaksaresharperandnarrower,Thehigher2peaksforthehydroxidesystemcanalsobeobservedafterheattreatment.Thiscrystallitesizeafterheattreatmentat500and1000grewto8.8and47.4nm,respectively,Thesamplesfromtheceriaacetatesystemexhibitedalargerdegreeofcrystallinitythanceriumhydroxidesystem.Thecrystallitesizefortheceriaacetatesystemafterheattreatmentwas17.7and53.6nmat500and1000,respectively,Fig.10TEMandelectrondiffractionpatternofCeO2fromcerium(IV)hydroxide(a)andceriaacetate(b)after24hhydrothermaltreatment.,Fig.10(a)exhibitedveryfineparticles,whichwereagglomerated.Crystallinitycouldbeobservedbasedontheparticlesanditscorrespondingelectrondiffractionpattern.Itscrystallitesizeisabout56nmasestimatedfromtheTEMmicrographs.Theparticlesgenerallyshownroundededgesbuttheyarenotwell-definedduetoitssmallsize,Fig.10(b),particlesareverywell-definedandrelativelydispersed.Goodcrystallinefacesandcrystallinitystatecouldbeobserved,Theparticlesizes,atabout1015nm,areslightlybiggercomparedtothecerium(IV)hydroxidesystem.ceriaacetatesystemappearstobelessagglomeratedthanthecerium(IV)hydroxidesystem.However,agglomerationoftheparticlesstillappearstobeaproblem.,Salt-assistedultrasonicaerosoldecomposition,Salt-assistedaerosoldecomposition(SAD),Conventionalaerosoldecomposition(CAD),thesameoperatingconditions,thesameexperimentalapparatus,withoutthesalts,B.Xia,I.W.LenggoroandK.Okuyama,HiroshimaUniversity,Japan,J.Mater.Chem.,2001,11,29252927,Resultsanddiscussion,Fig.1SubmicrontomicronCeO2particlessynthesizedbytheCADmethodat800:(a)lowermagnificationimage;(b)highermagnificationimageoftheparticlemarkedA,comprisingsinterednano-crystallites.,Theparticles(Fig.1a)aresolidandnearlysphericalwithameanparticlesizeof0.74um,Fig.1showstheTEMimagesoftheCeO2particles,whichweresynthesizedbytheCADmethodat800,Consistofnanosizedcrystallites(Fig.1b)withmeansizeof13.8nmdeterminedbytheX-raydiffraction(XRD)technique.Thesenanosizedcrystallitesarevirtuallyinseparableduetosintering,Fig.2NanometernanosizedCeO2particlessynthesizedbytheSADmethodat(a)800,and(b)atypicalhighresolutionTEMimageofsample(a),showingthecrystallatticeofaparticle,ImportantdifferencesbetweentheCADandtheSADproductsareindicatedbelow:,First,theSADproduct(Fig.2a)iscomposedofisolatednanoparticles(meansize51nm),whiletheCAD(meansize0.74mm)containingsinterednano-crystallites,Second,theSADCeO2particlesaresinglecrystalswhiletheCADCeO2particlesarepolycrystalline(asshowninFig.1b)Thesinglecrystalsareevidencedbytheagreementbetweentheparticlesizesandthecrystalliteonesatallsynthesistemperatures,asshowninTable1.ThetypicalcrystallatticeimageshowninFig.2bconfirmsthepresenceofsinglecrystallineparticlesClearly,theparticlesizedistributionoftheSADproducthasbeenremarkablynarrowedincomparisontotheCADproduct,Table1Comparisonofparticleandcrystallitediameters(inanometers)ofCeO2synthesizedbytheCADandtheSADprocesses,Fig.3PowderXRDpatternsofroductssynthesizedat(a)CAD,800(CeO2);(b)SAD,800(CeO2),Third,theSADproducthasamuchhighercrystallinitythantheCADproduct,asshownfromthesharppeaksinFig.3b.ThecrystallitesizeoftheSAD800sampleis54.4nm,asshowninTable1.ThisismuchlargerthanthecorrespondingCADsample,DetailsoftheSADprocess:CeO2canparticipateindissolutionandprecipitationintheliquid-statesaltmedia,whichcangreatlyfacilitatemasstransferandthusmaterialformationandcrystallizationprocessesAcrystallitegrowsbydepletingitsadjacentcrystallitesandisthenisolatedfromothersdu