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Shape-controlled synthesis of nanocubic Co3O4 by hydrothermal oxidation method

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Shape-controlled synthesis of nanocubic Co3O4 by hydrothermal oxidation method

    Shape-controlled synthesis of nanocubic

    Co3O4 by hydrothermal oxidation

    method

    Science

    Press

    Availableonlineatwww.sciencedirect.com

    ?C?EHCEDlRECT0

    Trans.NonferrousMet.Soc.China17(2007)10821086

    ShapecontrolledsynthesisofnanocubicCo304by

    hydrothermaloxidationmethod

    Transactionsof

    NonferrousMetals

    SocietyofChina

    YANGYou-ping(杨幼平),HUANGKelong(黄可龙),LIURen-sheng(刘人生),

    WANGLi-ping(~丽平),ZENGWen-wen(~雯雯),ZHANGPingmin(张平民)

    www.CSU.edu.cn/ysxb/

    SchoolofChemistryandChemicalEngineering,CentralSouthUniversity,Changsha410083,China

    Received30December2006;accepted9April2007

    Abstract:ThenanocubicCo304wassynthesizedbyhydrothermaloxidationmethod.111eeffectsofcobaltsalt,precipitatingagent,

    surfactant,solvent,pHvalueofthesuspensionandtheamountofoxidantH202onthemorphologyandstructureofCoO4were

    investigated.11

    eCo04powderswerecharacterizedbytransmissionelectronmicroscopeandX.raydiffraction.Theresultsshow

thatthemorphologyofCo304iscloselydependantontheanionincobaltsalts,butitisnotsosen

    sitivetotheprecipitatingagentsand

    solvents.Theanaountof}{,O2isthekeyfactortoobtainCoO4,

    Irithspinelcrystalstructure.Theoptimumsyntheticconditionsof uniformshape-controlledCo304nanocubesareasfollows:Co(CH3COO)2'4H20ascobalts

    alt,KOHasprecipitatingagent,

    polyethyleneglycolwithrelativemolecularmassofabout200o0assurfactant,water-n

    butanolassolventsystem,pHvalueof89,

    themolarratioOfH202toCoabove2.5:1.0,hydrothermaltemperatureof160?

    andhydrothermalholdingtimeofl0h.Thetap

    densityandapparentdensityofnanocubicCo304obtained,

    Irimtheaverageparticlesizeof20nlllare1.01g/cnljand0.70cm, respectively.

    Keywords:Co304;nanocubes;shapecontrolled;hydrothermaloxidation 1Introduction

    ThetricobalttetraoxideCo3O4belongstothe

    normalspinelcrystalstructurebasedonacubicclose packingarrayofoxideatoms,inwhichCoionsoccupy thetetmhedral8asitesandCoionsoccupythe

    octahedral16dsites.Inrecentyears,Co3O4hasattracted attentionduetoitswideapplicationsincatalysts[1], magneticsemiconductors[2],electrodematerial[3(5],

    gassensors[5]andpressuresensitiveceramics[6]. Variousmethods,suchasthethermaldecompositionof solidphase[7(8],solgelmethod[9],hydrothermal

    method[1011],solvothermaldecomposition[12],

    chemicalvapordeposition[13],liquidcontrol-

    precipitationmethod[14]andspraypyrolysis[15],were attemptedtosynthesizenanosizedspinelCo304.Itis

    wellknownthatthebehaviorsofnanophasematerials stronglydependontheshapeandsizeoftheparticles[5]. Andhydrothermaloxidationmethodisanefficient techniqueforpreparingfineuniformparticlesofmetal oxides[161.

    ZHANGetall101studiedtheeffectsofhydro.

    thermalsyntheticconditions,suchasthestarting concentrationofCo(NO3)2solution,pHvalue, hydrothermaltemperature,holdingtimeandthestocking mode,ontheshapeandsizeofCo3O4cubesin

    Co(NO3)2NH3"H20system.TheCo304andCo(OH)2

    mixtureswereobtainedwhenthetemperaturewasbelow l80?andhydrothermalholdingtimewas1-36h.and thecubicCo3O4couldbeobtainedbycalciningthe mixturesinair.JIANGetal[11reportedthatCo(OH)2

    gel,whichwaspreparedusingCoSO4'7H20and

    NH3"H:20asstartingmatedals.couldbeoxidizedto nanocrystallineCo304byhydrogenperoxideina hydrothermalsystemat180?for24h.Although

    Co(OH)2gelwasfilteredusingvacuumfiltrationand washedbydistilledwaterforseveraltimesuntilno sOandNH;remained,themorphologyof

    nanocrystallineC~o304wasirregular.Inorderto synthesizeuniformshapecontrolledCo3O4nanocubes,

    theeffectsofanionincobaltsalt,precipitatingagent, surfactant,solvent,pHvalueofthesuspension,andthe amountofoxidantH2O,ont}lemorphologyandstructure Foundationitem:Project(50542004)supposedbytheNationalNaturalScienceFoundation

    ofChina;Project(ZE097)suppoaedbyCreativeProgramof CentralSouthUniversity,China

Correspondingauthor:HUANGKelong;Tel:+867318879850;E

    mail:klhuang@mail.CSU.edu.cn

    YANGYouping,etal/Trans.NonferrousMet.Soc.China17(2007) ofCo304wereinvestigatedinthisstudy

    2Experimental

    15mmoLcobaltsaltwasdissolvedintodistilled watercontainingcertainsurfactantandorganicsolvent, andthenexcessiveamountofprecipitatingagentwas addedwithelectromagneticstingat30?duringthe

    formationofCo(OH)2precursor.ThepHvalueofthe suspensionafterprecipitationreactionwasmonitoredto 8-9.Acertainamountof30%fmassfraction)H,O,was droppedintothesuspension.Finally,al1ofthemwere ansferredintoaTeton.1inedstainlessstee1autoclave withthevolumeof100mL.andtheautoclavewasfilled withdistilledwateruDto70%ofthetota1capacity.The sealedautoclavewasheatedto160?andmaintained

    forl0h.thencooledtoroomtemperatureinairnaturally Theblackpowderswerecentrifugedandwashedwith distilledwaterandabsoluteethano1forthreetimes. respectively,anddriedinanovenat80?for6h.

    Themorphologyandsizeoftheobtainedpowders weredeterminedbyusingaJapanJE0LJEM(1230

    1083

    transmissionelectronmicroscopy(TEM).TheX-ray diffraction(XRD)patternsofthepowderswereobtained withaJapanRigakuD/max-2500X-raydiffi'actometer usingCuradiationinthe20rangefrom10.to80.. 3Resultsanddiscussion

    3.1Effectofeobaltsaltandprecipitatingagent Fig.1showstheTEMimagesofCo3O4using

    differentcobaltsaltsandprecipitatingagentsinthe presenceofpolyethyleneglycolwithrelativemolecular massofabout20000(PEG20ooo)andwater-n.butano1 solventsystem.ItcanbeseenfromFigs.1fa)and(d)that themorphologiesofCo304areirregularnanocubesusing CofNO3)2?6H20ascobaltsaltandKOHorNH3.NH4C1 buffersolutionasprecipitatingagent.Forcomparison typicalsphericalCo304andnanocubicCo3O4are obtainedwhenthecobaltsaltsareCoSO4"7H2Oand Co(CH3COO)2'4H20,respectively,asshowninFigs.1(b) andfc).Itcanbeconcludedthatthemorphologiegof Co3O4arecloselydependantontheaniontypeincobalt salts.Inotherwords.theaniontypeincobaltsaltplaysa Fig.1TEMimagesofCO304synthesizedwithdifferentcobaltsaltsandprecipitatingagents:(

    a)Co(NO3)2andKOH;Co)CoSO4and

    KOH;C)Co(CH3CO0)2andKOH;(d)CoCN03)2andNH3NH4C1buffersolution

    1084YANGYou-ping,etal/Trans.NonferrousMet.Soc. China17(2007)

    keyroleinthemorphologyofC0304,whiletheinfluence ofprecipitatingagentonthemorphologyofCo304is verylimited.Therefore,Co(CH3COO)2"4H2OandKOH arechosenascobaltsaltandprecipitatingagentto synthesizenanocubicCo3O4,respectively.

    3.2EflfectOfsurfactant

    Fig.2showstheeffectsofsurfactantonmorphology ofCo3O4inwater-n.butanolsolventsystem.Itcanbe seenthatnanocubicCo3O4synthesizedinthepresenceof

    nonionicsurfactantPEG20000ishighlydispersedand showsexcellentuniformity,whileCo3O4nanoparticles obtainedfromanionicsurfactantsodiumdodecyl benzenesulfonate(SDBS)areagglomeratedinirregular shapes.Tl1ismaybeduetotheinterfaceretardingeect

    ofPEG20000.TherelativemolecularmassofPEG 20000isgreaterthanthatOfSDBS.Asaresult.PEG 20000ischosenasthesurfactantinthesynthesisof nanocubicCo3O4.

    3.3EffectofpHvalue

    Fig.2TEMimagesofCo304synthesized,lrimdifferent

    surfactants:(a)Polyethyleneglycol20000;(b)Sodium dodecylbenzenesulfonate

    Fig.3showstheTEMimageofCo3O4synthesized insuspensionofpH1112afterprecipitationreaction. ComparedFig.1(c)withFig.3,itisveryobviousthat nanocubicCo304withtheaverageparticlesizeof20nln isformedwhenpHis8-9,andwhenpHgoesupto 1112irregularCo304includingsomegrains recombinedintheproductsbecomesserious.Because thecondensationreactionofCo(OH)2precursorcan easilyOCCUrathigherpHvalue,agglomerationofthe nanoparticlesOCCURS.

    Fig.3TEMimageofCo3O4synthesizedinsuspensionofpH l1-12

    ThecondensationreactionofCo(OH)2canbe expressedas

    H2O

    (1)

    InordertosynthesizenanocubicCo304,thepH

    valueofsuspensionshouldbestrictlycontrolledat8-9. 3.4Effectofsolvent

    TheXRDpatternsofCo3Odsynthesizedindifferent solventsystemsareshowninFig.4.A11peaksshownin Fig.4canbeindexedtoacubicspinelcrystalstructure Co304.Noimpuritypeaksareobserved,whichindicates thatthefinalproductsynthesizedisCo3Odwithspinel crystalstructureunderhydrothermaloxidationcondition. BasedonScherrerformula,theaverageparticlesizesof Co3Odinwater,water-alh0landwater.butanol

    solventsystemsarecalculatedtobe27nlTI.10nmand 15nrn,respectively.

    Fig.5showstheTEMimagesofCo304synthesized inwaterandwater-alcoho1solventsystemsusing Co(CH3COO)2'4H20ascobaltsalt.ComparedFig.1(c) withFig.5,itcanbeseenthatnanocubicCo3O4particles areallobtainedinthesesolventsystems.WhileCo3O4 synthesizedinwater-n.butanolsolventsystemshowsa

    YANGYou.ping,etalfWrans,NonferrousMet.Soc,China17(2007)1085 3.5EffectofamountofH202

    20/(.)

    Fig.4XRDpaRemsofCo304synthesizedindifferentsolvent systems:(a)Water;(b)Water-alcohol;(c)Water--n?butanol Fig.5TEMimagesofCo304synthesizedindifferentsolvent systems:(a)Water;(b)Water--alcohol

    be~ermonodispersesign(Fig.1(c)),andthetapdensity andapparentdensityofuniformshapecontrolledCo304

    nanocubesare1.olg/cmand0.70g/cmrespectively. InordertogetCo304withspinelcrystalstructure,

    theamountofoxidantH2O2shouldbeenough.The chemicalreactioninthehydrothermaloxidationprocess Canbeexpressedas

    3Co(OH)2+H202-~C0304+4H20(2)

    SothemolarratioofH202toCo(OH)2isl:3in

    theory.However,H2O2tendstodecomposeinthe practicaloperation,thereforetheamountOfH2O2iSfar morethanthetheoreticalvalue.

    Fig.6showstheXRDpaRernsofthesamples

    obtainedwithaddingdifferentamountofH2O2.Whell themolarratioOfH20,toCois2.0:1.0,theimpurity Co(OHstillexists.WhilethemolarratioofH202to CoiSincreasedto2.5:1.0,Co3O4withcubicspinel crystalstructureisobtained.SoinordertoobtainCo3O4 withspinelcrystalstructure,themolarratioOfH2O2to Coshouldbehigherthan2.5:1.0.

    20/(.)

    Fig.6XRDpatternsofCo304synthesizedwithdifferentmolar ratiosofH2O2toCo:(a)2.0:1.0;(b)2,5:1,0

    4Conclusions

    l1Theuniformshape.controlledspinelCoO4

    nanocubeiSpreparedbyhydrothermaloxidationmethod. TheoptimumsyntheticconditionsofCo3O4nanocubes areasfollows:Co(CH3COO-4H2Oascobaltsalt,K0H asprecipitatingagent,polyethyleneglycol20000as Sill"factant,pHvalueof8-9.molarratioofH,0,toCo above2.5:1.0.hydrothermaltemperatureof160?and

    hydrothermalholdingtimeofl0h.

    2)ThemorphologyofCo304iscloselydependant ontheanionincobaltsalts.Thenanocrystalline

    sphericalanduniformnanocubicCo3O4particlesare obtainedusingCo(NO3)2'6H20,COSO4'7H20and Co(CH3COO)2'4H20ascobaltsalts,respectively. 3,Theprecipitatingagentandsolventsystemhave littleinfluenceonmorphologyofCo304.TheCo304 nanocubesareallsynthesizedinwater,water-alcohol

1086YANGYou-ping,etal/Tr~s.

    NonferrousMet.Soc.China17(2007)

    andwater--n-butanolsolventsystems,andtheaverage particlesizesofCo304arecalculatedtobe27.10andl5 nm,respectively.,rhetapdensityandapparentdensit)rof uniformshapecontrolledCo304nanocubessynthesized inwater--n-butanolsolventsystemare1.01and 0.70g/cIIlj,respectively.

    4)TheamountofH202isthekeyfact0rtoobtain Co3O4,)l,ithspinelc~smlstructure.Themolarratioof H2O2toCoshouldbehigherthan2.5:1.0.

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