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 T 950 还原后 CeO2转化为具有氧空位 非化学计量比的CeO2 X氧化物 0 x 0 5 而在低温下 T 450 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 washedthricewithdistilledwaterandalcoholanddriedat80 overnight Resultsanddiscussion SEMphotoesofprecursor XRDofprecursor a Ce NO3 3 NH3 H2O b NH4 2Ce NO3 6 NH3 H2O 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 H2O CO2 2NH3NH3 H2O NH4 OH CO2 H2O CO32 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 217 222 2 Ceriaacetateprecursor Fig 1 DTA TGofCe OH 4precursor Resultsanddiscussion Thetotalmeasuredweightlossfrom25to900 was11 64 whilethetheoreticalweightlossforthedecompositionofceriumhydrateoxideis17 3 i e Ce OH 4 CeO2 2H2OtoCeO2 ThedecompositionoftheprecursorisaformofdehydrationprocessofthehydratedCeO2 thedifferenceinweightlossobservedcouldbeduetothefollowingreasons a precipitateconsistingofapartiallyhydratedformofceria i e CeO2 xH2O forwhicha11 64 weightlossondecompositioncorrespondstox 1 35or b theprecipitateconsistedofamixtureofphaseslikeCeO2 2H2O CeO2 Fig 2DTA TGofceriaacetateprecursor Theprecursormeasuredatotalweightlossof12 55 withfourdistincttemperaturepeaks Thefirstendothermicpeakwasdetectedataround100 Thisisattributedtothereleaseofthewatermoleculespresentintheprecursor From100to200 theweightlosswasattributetotheremovalofthesurfaceacetategroupsandlatertheformationoftheaceticacidwhensurfaceacetatehydrolysisoccurs Thisalsoexplainstheveryweakendothermicpeakdetectedat200 Therewasasharpweightlossfrom200to400 andacorrespondingexothermicpeak 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 Thepeaksathigher2 anglescanalsobeclearlyobservedforallsamples Fig 6 LatticeconstantofCeO2afterhydrothermaltreatmentat250 usingCe OH 4precursor Fig 7LatticeconstantofCeO2afterhydrothermaltreatmentat250 usingceriaacetateprecursor thelatticeparameterdecreasedbyabout0 2 afterhydrothermaltreatmentat250 for6h From6to12hatthesametemperature thelatticeexpanded Thelatticeconstantonlyvariedwithinanarrowrange a a 0 03 after12h indicatingthatthestructurebecamestable Thelatticeconstantdecreasedbyabout0 5 afterhydrothermaltreatmentat250 Cfor6h Furtherchangesoflatticeconstantwereverysmallwhentreatmentdurationwasincreased Thevariationoflatticeconstantwaslessthan0 03 Fig 8CeO2fromCe OH 4 24h heattreatedat a 500 b 1000 Fig 9CeO2fromceriaacetate 24h heattreatedat a 500 b 1000 Inbothfigures itcanbeseenthatthecharacteristicpeaksaresharperandnarrower Thehigher2 peaksforthehydroxidesystemcanalsobeobservedafterheattreatment Thiscrystallitesizeafterheattreatmentat500and1000 grewto8 8and47 4nm respectively Thesamplesfromtheceriaacetatesystemexhibitedalargerdegreeofcrystallinitythanceriumhydroxidesystem Thecrystallitesizefortheceriaacetatesystemafterheattreatmentwas17 7and53 6nmat500and1000 respectively Fig 10TEMandelectrondiffractionpatternofCeO2fromcerium IV hydroxide a andceriaacetate b after24hhydrothermaltreatment Fig 10 a exhibitedveryfineparticles whichwereagglomerated Crystallinitycouldbeobservedbasedontheparticlesanditscorrespondingelectrondiffractionpattern Itscrystallitesizeisabout5 6nmasestimatedfromtheTEMmicrographs Theparticlesgenerallyshownroundededgesbuttheyarenotwell definedduetoitssmallsize Fig 10 b particlesareverywell definedandrelativelydispersed Goodcrystallinefacesandcrystallinitystatecouldbeobserved Theparticlesizes atabout10 15nm 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 2925 2927 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 ThecrystallitesizeoftheSAD800 sampleis54 4nm asshowninTable1 ThisismuchlargerthanthecorrespondingCADsample DetailsoftheSADprocess CeO2canparticipateindissolutionandprecipitationintheliquid statesaltmedia whichcangreatlyfacilitatemasstransferandthusmaterialformationandcrystallizationprocessesAcrystallitegrowsbydepletingitsadjacentcrystallitesandisthenisolatedfromothersdueto