氧化铈纳米粒子的制备ppt课件

Members:XianhongRuiYuChenLitaoYanHuaminYaoLiangjunYiDepartmentofMaterialsScienceandEngineeringUniversityofScienceandTechnologyofChinaJan3,200811.SimplyintroducethestructureandapplicationsofCeO23.Futureworks2.SynthesisofnanocrystallineCeO2bydifferentmethods2BriefintroductionCeO2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.StructureofCeO22.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(0x0.5)，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。3ApplicationsofCeO2玻璃脱色剂氧化铈大颗粒氧化铈磨料氧化铈抛光粉/液晶显示屏氧化铈抛光粉氧化铈抛光轮CeO2Slurry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4SynthesisofCeO21.DirectprecipitationprecipitationStirandageingstageScouringanddryingtocalcineprecursorThepowerofCeO2Ce3+orCe4+technologyofdirectprecipitationprecipitantNitrate:Ce(NO3)3or(NH4)2Ce(NO3)6Precipitant:ammoniaorNH4HCO3Surfaceactiveagent:PEG-4000Process:nitrateandPEG-4000weredissolvedindistilledwate.ThenammoniaorNH4HCO3solutionwasaddeddropwiseundervigorousstirringtillthepHreached9.Theprecipitatewasfiltered,washedthricewithdistilledwaterandalcoholanddriedat80℃overnight.5(a)(b)(c)(d)Resultsanddiscussion102030405060702(a)(b)(c)(d)SEMphotoesofprecursorXRDofprecursor(a):Ce(NO3)3+NH3·H2O(b):(NH4)2Ce(NO3)6+NH3·H2O(c):Ce(NO3)3+NH4HCO3(d):(NH4)2Ce(NO3)6+NH4HCO36102030405060700500100015002000250030002(a)(c)XRDofCeO2synthesizedat700℃10203040506070(a)(b)(c)(d)XRDofCeO2synthesizedat500℃102030405060702(a)(c)XRDofCeO2synthesizedat600℃7(a)(c)SEMphotoesofCeO2calcinedat600℃8MicrowavehomogeneousprecipitationMicrowavereactionequipmentNitrate:Ce(NO3)3or(NH4)2Ce(NO3)6Precipitant:ureaSurfaceactiveagent:PEG-4000CO(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9Resultsanddiscussion102030405060702XRDofprecursorcalcinedat500℃(a)(b)(c)102030405060700501001502002502XRDofprecursor(a)Mean:(a)0.093um(b)0.171um(c)0.210umLSofCeO2calcinedat600℃(a)Ce(NO3)3+urea,withoutPEG-4000(b)Ce(NO3)3+urea+PEG-4000(c)(NH4)2Ce(NO3)6+urea+PEG-4000101020304050607005001000150020002600℃700℃XRDofCeO2synthesizedat600℃、700℃SEMphotoofCeO2calcinedat600℃SEMphotoofprecursor(a)11HydrothermalsynthesisofCeO2nano-particles1.Cerium(IV)hydroxideprecursorA.I.Y.Tok,etal(NanyangTechnologicalUniversity),JournalofMaterialsProcessingTechnology190(2007)217–222H2O2+cerium(III)nitrate,stirredfor5minunderheattoconvertCe3+toCe4++ammonia(pH=8.8),stircontinuouslyat80℃for1hthepaleyellowprecipitates(Ce(OH)4)werewashed,theconductivityofthesupernatant=2ms30mlofthewashedprecipitates(pH=10)wereplacedintotheTeflonvesselofthehydrothermalbomb,thenplacedintheovenandheatedattherespectivedurations(0–24h)Thefinalproductswerere-washed,conductivity=2ms,driedat75℃122.Ceriaacetateprecursorhydrousceriumoxidestabilizedbyacetateions(ceriumacetategel)wasdissolvedindeionizedwatertoyield‘acetatestabilizedcolloidalceriaandwillbeidentifiedasceriaacetateceriaacetatewasdiluted,placing30mlofthesolutionintotheTeflonvesselthebombwasthenplacedintheovenandheatedto250℃atdifferenttreatmenttimestheproductswerelatercentrifugedanddriedat75℃13Fig.1.DTA/TGofCe(OH)4precursorResultsanddiscussionThetotalmeasuredweightlossfrom25to900℃was11.64%,whilethetheoreticalweightlossforthedecompositionofceriumhydrateoxideis17.3%,i.e.Ce(OH)4/CeO2·2H2OtoCeO2ThedecompositionoftheprecursorisaformofdehydrationprocessofthehydratedCeO2thedifferenceinweightlossobservedcouldbeduetothefollowingreasons:(a)precipitateconsistingofapartiallyhydratedformofceria,(i.e.CeO2·xH2O),forwhicha11.64%weightlossondecompositioncorrespondstox=1.35or(b)theprecipitateconsistedofamixtureofphaseslikeCeO2·2H2O+CeO214Fig.2DTA/TGofceriaacetateprecursorTheprecursormeasuredatotalweightlossof12.55%withfourdistincttemperaturepeaksThefirstendothermicpeakwasdetectedataround100℃.ThisisattributedtothereleaseofthewatermoleculespresentintheprecursorFrom100to200℃,theweightlosswasattributetotheremovalofthesurfaceacetategroupsandlatertheformationoftheaceticacidwhensurfaceacetatehydrolysisoccurs.Thisalsoexplainstheveryweakendothermicpeakdetectedat200℃Therewasasharpweightlossfrom200to400℃andacorrespondingexothermicpeak.Thisexothermicpeaksuggeststheformationofoxyacetateanddioxocarbonatecomplexeswithcerium,Ce(OH)(CH3COO)andCe2O2CO3Astemperatureincreasedto700℃,theCe2O2CO3decomposedendothermallytoproducethefinalproductCeO215Fig.3DTA/TGforCeO2synthesizedfromceriaacetate:(a)after6htreatment;(b)after24htreatmentafter6and24hofhydrothermaltreatment,weightlossisdramaticallyreducedto2.64and1.37%Thedistincttemperaturepeaksaresimilartothatoftheprecursor.However,thedistinctexothermicpeakforthehydrothermaltreatedsamplesisnolongeraspronouncedasthatoftheprecursorThiscouldbeduetotheamountofacetatecomplexesformationbeingreducedconsiderablyafterhydrothermaltreatment.Tracesofceriumacetatecomplexeswerestillpresentinthesamplesafterhydrothermaltreat