氧化鈰納米粒子的制備

關(guān)于氧化鈰納米粒子的制備SimplyintroducethestructureandapplicationsofCeO23.Futureworks2.SynthesisofnanocrystallineCeO2bydifferentmethodsOutline第2頁,共27頁，2024年2月25日，星期天BriefintroductionCeO2屬于螢石型氧化物。

CeO2晶胞中的Ce4+按面心立方點(diǎn)陣排列，O2-占據(jù)所有的四面體位置，每個(gè)Ce4+被8個(gè)O2-包圍，而每個(gè)O2-則與4個(gè)Ce4+配位。1.StructureofCeO22.功能特性

CeO2的結(jié)構(gòu)中有1/2立方體空隙，可稱之為敞型結(jié)構(gòu)。敞型結(jié)構(gòu)允許離子快速擴(kuò)散。經(jīng)高溫(T＞950℃)還原后，CeO2轉(zhuǎn)化為具有氧空位、非化學(xué)計(jì)量比的CeO2-X氧化物(0<x<0.5)，而在低溫下(T＜450℃)CeO2可形成一系列組成各異的化合物。值得注意的是，即使從晶格上失去相當(dāng)數(shù)量的氧，形成大量氧空位之后，CeO2仍然能保持螢石型晶體結(jié)構(gòu)，這種亞穩(wěn)氧化物暴露于氧化環(huán)境時(shí)又易被氧化為CeO2，因而CeO2具有優(yōu)越的儲存和釋放氧功能及氧化還原反應(yīng)能力，同時(shí)CeO2也有著良好的化學(xué)穩(wěn)定性和高溫快速氧空位擴(kuò)散能力。

第3頁,共27頁，2024年2月25日，星期天ApplicationsofCeO2

玻璃脫色劑氧化鈰大顆粒氧化鈰磨料氧化鈰拋光粉/液晶顯示屏氧化鈰拋光粉氧化鈰拋光輪CeO2Slurry

此外，CeO2還用作催化材料、高溫氧敏材料、pH傳感材料、電化學(xué)池中膜反應(yīng)器材料、燃料電池的中間材料、中溫固體氧化物燃料電池(SOFC)用電極材料第4頁,共27頁，2024年2月25日，星期天SynthesisofCeO21.DirectprecipitationprecipitationStirandageingstageScouringanddryingtocalcineprecursorThepowerofCeO2Ce3+orCe4+technologyofdirectprecipitationprecipitantNitrate:

Ce(NO3)3or(NH4)2Ce(NO3)6Precipitant:

ammoniaorNH4HCO3

Surfaceactiveagent:

PEG-4000Process:nitrateandPEG-4000weredissolvedindistilledwate.ThenammoniaorNH4HCO3solutionwasaddeddropwiseundervigorousstirringtillthepHreached9.Theprecipitatewasfiltered,washedthricewithdistilledwaterandalcoholanddriedat80℃overnight.第5頁,共27頁，2024年2月25日，星期天(a)(b)(c)(d)Resultsanddiscussion(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+NH4HCO3第6頁,共27頁，2024年2月25日，星期天(a)(c)XRDofCeO2synthesizedat700℃(a)(b)(c)(d)XRDofCeO2synthesizedat500℃(a)(c)XRDofCeO2synthesizedat600℃第7頁,共27頁，2024年2月25日，星期天(a)(c)SEMphotoesofCeO2calcinedat600℃第8頁,共27頁，2024年2月25日，星期天MicrowavehomogeneousprecipitationMicrowavereactionequipmentNitrate:Ce(NO3)3or(NH4)2Ce(NO3)6Precipitant:

ureaSurfaceactiveagent:

PEG-4000CO(NH2)2+H2O→CO2+2NH3NH3+H2O→NH4++OH-CO2+H2O→CO32-+2H+

水解生成的構(gòu)晶離子OH-、CO32-,在微波輻照作用下,與Ce3+、Ce4+等結(jié)合生成不溶前驅(qū)物

第9頁,共27頁，2024年2月25日，星期天ResultsanddiscussionXRDofprecursorcalcinedat500℃(a)(b)(c)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-4000第10頁,共27頁，2024年2月25日，星期天600℃700℃XRDofCeO2synthesizedat600℃、700℃

SEMphotoofCeO2calcinedat600℃SEMphotoofprecursor(a)第11頁,共27頁，2024年2月25日，星期天HydrothermalsynthesisofCeO2nano-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℃第12頁,共27頁，2024年2月25日，星期天2.Ceriaacetateprecursorhydrousceriumoxidestabilizedbyacetateions(ceriumacetategel)wasdissolvedindeionizedwatertoyield‘a(chǎn)cetatestabilizedcolloidalceriaandwillbeidentifiedasceriaacetateceriaacetatewasdiluted,placing30mlofthesolutionintotheTeflonvesselthebombwasthenplacedintheovenandheatedto250℃atdifferenttreatmenttimestheproductswerelatercentrifugedanddriedat75℃第13頁,共27頁，2024年2月25日，星期天Fig.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+CeO2第14頁,共27頁，2024年2月25日，星期天Fig.2DTA/TGofceriaacetateprecursorTheprecursormeasuredatotalweightlossof12.55%withfourdistincttemperaturepeaksThefirstendothermicpeakwasdetectedataround100℃.ThisisattributedtothereleaseofthewatermoleculespresentintheprecursorFrom100to200℃,theweightlosswasattributetotheremovalofthesurfaceacetategroupsandlatertheformationoftheaceticacidwhensurfaceacetatehydrolysisoccurs.Thisalsoexplainstheveryweakendothermicpeakdetectedat200℃Therewasasharpweightlossfrom200to400℃andacorrespondingexothermicpeak.Thisexothermicpeaksuggeststheformationofoxyacetateanddioxocarbonatecomplexeswithcerium,Ce(OH)(CH3COO)andCe2O2CO3Astemperatureincreasedto700℃,theCe2O2CO3decomposedendothermallytoproducethefinalproductCeO2第15頁,共27頁，2024年2月25日，星期天Fig.3DTA/TGforCeO2synthesizedfromceriaacetate:(a)after6htreatment;(b)after24htreatmentafter6and24hofhydrothermaltreatment,weightlossisdramaticallyreducedto2.64and1.37%Thedistincttemperaturepeaksaresimilartothatoftheprecursor.However,thedistinctexothermicpeakforthehydrothermaltreatedsamplesisnolongeraspronouncedasthatoftheprecursorThiscouldbeduetotheamountofacetatecomplexesformationbeingreducedconsiderablyafterhydrothermaltreatment.Tracesofceriumacetatecomplexeswerestillpresentinthesamplesafterhydrothermaltreatment.Theamountishowever,significantlylowerthanthatfoundintheprecursor第16頁,共27頁，2024年2月25日，星期天Fig.4CeO2usingCe(OH)4precursor(250℃)asafunctionoftimeFig.5CeO2usingceriaacetateprecursor(250℃)asafunctionoftimeFig.4,thenano-particlesexhibitedsomedegreeofcrystallinityanddisplayedallofthemajorpeaksofCeO2withacubicstructureafter6htreatmentNosignificantimprovementincrystallinitywasobservedbetween6and24h,andthepeakswerebroadwithweakintensities.ThistrendissimilarwiththeceriaacetatesystemFig.5,thepeaksaresignificantlynarrowerwithhigherintensitiessuggestinglargercrystallitesizesatanaverageof15.5nmascalculatedandlargerdegreeofcrystallinityascomparedtothecerium(IV)hydroxidesystem.Thepeaksathigher2θanglescanalsobeclearlyobservedforallsamples第17頁,共27頁，2024年2月25日，星期天Fig.6.LatticeconstantofCeO2afterhydrothermaltreatmentat250℃usingCe(OH)4precursorFig.7LatticeconstantofCeO2afterhydrothermaltreatmentat250℃usingceriaacetateprecursorthelatticeparameterdecreasedbyabout0.2%afterhydrothermaltreatmentat250℃for6h.From6to12hatthesametemperature,thelatticeexpanded.Thelatticeconstantonlyvariedwithinanarrowrange(|a|/a≈0.03%)after12h,indicatingthatthestructurebecamestable.Thelatticeconstantdecreasedbyabout0.5%afterhydrothermaltreatmentat250?Cfor6h.Furtherchangesoflatticeconstantwereverysmallwhentreatmentdurationwasincreased.Thevariationoflatticeconstantwaslessthan0.03%第18頁,共27頁，2024年2月25日，星期天Fig.8CeO2fromCe(OH)4(24h)heattreatedat(a)500℃,(b)1000℃Fig.9CeO2fromceriaacetate(24h)heattreatedat(a)500℃,(b)1000℃Inbothfigures,itcanbeseenthatthecharacteristicpeaksaresharperandnarrowerThehigher2θpeaksforthehydroxidesystemcanalsobeobservedafterheattreatment.Thiscrystallitesizeafterheattreatmentat500and1000℃grewto8.8and47.4nm,respectivelyThesamplesfromtheceriaacetatesystemexhibitedalargerdegreeofcrystallinitythanceriumhydroxidesystem.Thecrystallitesizefortheceriaacetatesystemafterheattreatmentwas17.7and53.6nmat500and1000℃,respectively第19頁,共27頁，2024年2月25日，星期天Fig.10TEMandelectrondiffractionpatternofCeO2fromcerium(IV)hydroxide(a)andceriaacetate(b)after24hhydrothermaltreatment.Fig.10(a)exhibitedveryfineparticles,whichwereagglomerated.Crystallinitycouldbeobservedbasedontheparticlesanditscorrespondingelectrondiffractionpattern.Itscrystallitesizeisabout5–6nmasestimatedfromtheTEMmicrographs.Theparticlesgenerallyshownroundededgesbuttheyarenotwell-definedduetoitssmallsizeFig.10(b),particlesareverywell-definedandrelativelydispersed.GoodcrystallinefacesandcrystallinitystatecouldbeobservedTheparticlesizes,atabout10–15nm,areslightlybiggercomparedtothecerium(IV)hydroxidesystem.ceriaacetatesystemappearstobelessagglomeratedthanthecerium(IV)hydroxidesystem.However,agglomerationoftheparticlesstillappearstobeaproblem.第20頁,共27頁，2024年2月25日，星期天Salt-assistedultrasonicaerosoldecompositionSalt-assistedaerosoldecomposition(SAD)Conventionalaerosoldecomposition(CAD)thesameoperatingconditions,thesameexperimentalapparatus,withoutthesaltsprecursorsolution:ceriumnitratewasdissolvedindistilledwatera

mixtureofpotassiumandsodiumnitrateswasaddedtotheprecursorsolutionthesolutionwasmistedbyanultrasonictransducer(1.7MHz)intodropletscarriedbyairintoahottubularreactorwheretheywererapidlyheatedanddecomposedtoformparticles,heatingtimewaslessthanfivesecondsCeO2

wereobtainedbywashingtheproductinwatertoremovethesaltsortheirderivativesB.Xia,I.W.LenggoroandK.Okuyama,HiroshimaUniversity,Japan,J.Mater.Chem.,2001,11,2925–2927第21頁,共27頁，2024年2月25日，星期天ResultsanddiscussionFig.1SubmicrontomicronCeO2particlessynthesizedbytheCADmethodat800℃:(a)lowermagnificationimage;(b)highermagnificationimageoftheparticlemarkedA,comprisingsinterednano-crystallites.Theparticles(Fig.1a)aresolidandnearlysphericalwithameanparticlesizeof0.74umFig.1showstheTEMimagesoftheCeO2particles,whichweresynthesizedbytheCADmethodat800℃Consistofnanosizedcrystallites(Fig.1b)withmeansizeof13.8nmdeterminedbytheX-raydiffraction(XRD)technique.Thesenanosizedcrystallitesarevirtuallyinseparableduetosintering第22頁,共27頁，2024年2月25日，星期天Fig.2NanometernanosizedCeO2particlessynthesizedbytheSADmethodat(a)800℃,and(b)atypicalhighresolutionTEMimageofsample(a),showingthecrystallatticeofaparticleImportantdifferencesbetweentheCADandtheSADproductsareindicatedbelow:First,theSADproduct(Fig.2a)iscomposedofisolatednanoparticles(meansize51nm),whiletheCAD(meansize0.74mm)containingsinterednano-crystallitesSecond,theSADCeO2particlesaresinglecrystalswhiletheCADCeO2particlesarepolycrystalline(asshowninFig.1b)Thesinglecrystalsareevidencedbytheagreementbetweentheparticlesizesandthecrystalliteonesatallsynthesistemperatures,asshowninTable1.ThetypicalcrystallatticeimageshowninFig.2bconfirmsthepresenceofsinglecrystallineparticlesClearly,theparticlesizedistributionoftheSADproducthasbeenremarkablynarrowedincomparisontotheCADproduct第23頁,共27頁，2024年2月25日，星期天Table1Comparisonofparticleandcrystallitediameters(inanometers)ofCeO2synthesizedbytheCADandtheSADprocessesFig.3PowderXRDpatternsofroductssynthesizedat(a)CAD,800℃(CeO2);(b)SAD,800℃(CeO2)Third,theSADproducthasamuchhighercrystallinitythantheCADproduct,asshownfromthesharppeaksinFig.3b.ThecrystallitesizeoftheSAD800℃sampleis54.4nm,asshowninTable1.ThisismuchlargerthanthecorrespondingCADsampleDetailsoftheSADprocess:CeO2canparticipateindissolutionandprecipitationintheliquid-statesaltmedia,whichcangreatlyfacilitatemasstransferandthusmater