revised4DDN.docx
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revised4DDN
Large-ScaleSynthesisofFlower-likeTeNanocrystalswithUniformBranchesbyaSurfactant-AssistedMethod
XingbaoWanga,,andWeipengGuanb,*
aXinhaiSeniorHighSchool,Lianyungang,Jiangsu,China222006;
bZhejiangGreatSoutheastPlasticGroupCorp.,Zhuji,Zhejiang,China311809
ABSTRACT
Flower-liketelluriumnanocrystalswithuniformbranchesweresuccessfullypreparedinlargequantitiesbyasurfactant-assistedmethod.TheproductwascharacterizedwithX-raydiffraction(XRD),scanningelectronicmicroscopy(SEM),transmissionelectronicmicroscopy(TEM),selectedareaelectronicdiffraction(SAED)andenergydispersiveX-rayspectroscopy(EDS).Thecharacterizationresultsrevealedthatthebranchofflower-likeTewasgrownalong[001]direction.Furthermore,theRamanspectrumoftheflower-liketelluriumwithuniformbrancheswasstudied.Theresultshowsthattheflower-likeTeexhibitsthreetypicalvibrationpeaks.Thisstudyprovidesasimplemethodtopreparethree-dimensionalTenanostructuresinlargescale,whichbroadstheirpracticalapplications.
Keywords:
Tellurium;Semiconductors;Microstructure;Morphology;Surfactant-assisted
1.Introduction
Inpastdecades,two-orthree-dimensionalnanostructureshavebeenthefocusofcurrentresearchonmicro-/nanomaterialsbecausepropertiesandapplicationsofthematerialsaredependentonthespatialarrangementandorientationofthenanocrystals[1-2].Todate,synthesisofcomplexmicro/nanostructures,includingfractalpatterns,dendrites,andotherhierarchicalstructures,hasattractedgreatattentionbecausestudiesonthesehyperbranchedstructuresareusefultofabricateelectronicorphotonicnanodevices[3].Recently,manyeffectivemethodsofsynthesizingfunctionalmaterialswithcomplexthree-dimensionalnanostructureshavebeendeveloped[4].However,inmostcase,forthefabricationofsuchsuperstructures,theemploymentofappropriateorganicligandorsurfactantisgenerallynecessaryastheshapemodifier[5].
Oneofthemostattractivematerialsistelluriumbecauseitexhibitsmanyfascinatingproperties,forexample,semiconductivity,thermoelectricity,nonlinearopticalresponses,uniquephotoconductivity,highpiezoelectricity,andcatalyticactivitytowardsomereactions[6-10].Inthepastfewdecades,telluriumwithdifferentmorphologiessuchasnanotubes,nanorods,nanowires,nanobelts,feather-likeandflower-likenanostructuresetc.havebeensynthesized[11-18].However,theexplorationof3DcomplexTestructuresbasedon1Dnanostructuresisstillanattractivefield,anditisstillchallengingtocontrolthemorphologiesof3DTenanostructuresoverawiderange.Toourbestknowledge,flower-likeTewithuniformbrancheshasn’tbeenpreparedinlargescale.Herein,3Dflower-liketelluriumnanocrystalswithuniformbrancheshavebeensynthesizedinlargescalebyasurfactant-assistedbiphasicsolvothermalapproach.Oursynthesisemploysdiethyldithiocarbamatotellurium(IV)(TDEC)dissolvedinchloroformasTesource,with2,2’-dithiodibenzoicacid(DTBA)andcetyltrimethylammoniumbromide(CTAB)dissolvedinNaOHsolutionlayeredabovetheaqueoussolutionasreducingagentandsurfactant,respectively.
2.ExperimentalSection
2.1Synthesisofflower-likeTewithuniformbranches
Flower-likeTenanocrystalswithuniformbrancheswerepreparedusingachemicalprocesssimilartothatdescribedbyWangetal[16].ThedifferenceliesintheuseofsurfactantCTAB.Acationicsurfactant(CTAB)waschosenbecauseitwasexpectedtohavestronginteractionwiththeanionicsurfacesofTecrystals[17].Diethyldithiocarbamatotellurium(IV)(TDEC)usedinthisexperimentwerecommercialgradeandrecrystallizedtwicefromhigh-puritychloroformpriortouseit.2,2’-dithiodibenzoicacid(DTBA),chloroform(CHCl3),sodiumhydroxide(NaOH)andcetyltrimethylammoniumbromide(CTAB)wereanalyticalgradeusedinthisstudywithoutfurtherpurification.Inatypicalprocedure,0.13mmolofTDEC,27.7mLofCHCl3,0.65mmolofDTBA,4.3mLof0.93mol.L-1NaOHand0.4gofCTABwereaddedinsequenceupto62%ofthetotalvolumewithoutstirring.Theautoclavewassealedandmaintainedat130oCfor3h,andthencooledtoroomtemperaturenaturally.Theobtainedblacksolidswerecollectedfromtheinterfaceoftwoimmisciblesolventsbycentrifugingthereactionmixture.Theproductswerethenwashedwithdistilledwaterandabsoluteethanolseveraltimesanddriedinavacuumatroomtemperatureforseveralhoursbeforefurthercharacterization.
2.2Characterization
ThemorphologywasexaminedwithaFEINovaNanosem200scanningelectronmicroscope(SEM),atransmissionelectronmicroscope(TEM)performedonaHitachiH-800transmissionelectronmicroscope(TEM)atanacceleratingvoltageof75kV,andahigh-resolutiontransmissionelectronmicroscope(HRTEM)(JEOL-2010)operatedatanaccelerationvoltageof200kV.TheChemicalcompositionwasconfirmedbyrecordingenergydispersiveX-rayanalysis(EDS),whilethestructuralinformationwasobtainedusingaBrukerD8AdvanceX-raydiffractometer(XRD)employingaCuKαradiationsource.TheRamanspectrumwasrecordedonaRenishawModel1000Ramanspectrometer,with514.5nmradiationfroma20mWair-cooledargonionlaserbeingusedastheexcitingsource.
3.Resultsanddiscussion
Fig.1showsthattheproductiswellcrystallizedelementaltellurium.Allthediffractionpeakscanbeindexedashexagonaltelluriumphase(JCPDS36-1452),andnootherpeakscanbefound.ItcanbeconcludedthathighpurityofhexagonalTewasobtainedbythepresentsyntheticmethod.
Fig.2ashowsapanoramicSEMimageoftheas-synthesizedproducts.AsshowninFig.2a,thesampleiscomposedof3Dnanomaterialswithabundantyield.Furtherobservationbasedonthehigh-magnificationimage(Fig.2b)revealsthattheflower-likenanostructuresarecomposedofuniformnanorodswithlengthsof4~7μmanddiametersofabout200nm.Itshouldbenotedthatthestructureofnanorodisdifferentfromthepreviousreport(i.e.,needle-likenanorods)[16].ItiswellknownthatthepresenceofCTABcaninfluencethenanocrystalgrowththroughchemicallyselectiveadsorptionontocertaincrystalfacesoftargetmaterials[17].Intheabsenceofsurfactant,needle-liket-TenanorodsgrowradicallyfromthecorebecauseoftheinherentanisotropicgrowthofTe[16].Thesurfactantwasabsolutelynecessaryforthegenerationofflower-likeTewithuniformbranches.ArepresentativeTEMimageofasmallflower-likeTeisshowninFig.2c.TheSAEDpatternofsinglenanorod(insetofFig.2d)revealsseveraldiffractionpoints,whichcanbeindexedtohexagonaltellurium.Fig.2dshowstheHRTEMimagerecordedonthenanorod,whichcouldbeverifiedthepreferredgrowthdirectionandthenatureofsinglecrystallineofthenanorods.Observedinterplanarspacingisabout0.60nm,whichcorrespondstotheseparationbetween(001)latticeplanesofhexagonalTe.Thismeansthatthenanorodsmightgrowalongapreferreddirectionof[001].
EDSanalysiswasusedtoanalyzethecompositionofthenanostuctures(Fig.3).StrongTepeaksundoubtedlyconfirmedthattheproductisTe.CuandCpeakscomefromthecarbon-coatedcoppergrid,whichisusedassamplesupporterduringmeasurementprocess.
TheRamanscatteringspectrumperformedonthesynthesizedflower-likeTenanocrystalsisdepictedinFig.4.ThesharpRamanlinesforthesampleshowsthepresenceofhexagonalTewithacharacteristicbandat96.5,124.8and144.9cm−1,respectively,whichareclosetotheresultsreportedpreviouslyontheTenanotubes[18].NootherbandsaredetectedbytheRamanspectra.ItisworthnotingthatthechangesofRamanpeakspositionsandline-shapeshaven’tbeenobserved,whichisdifferentfromtheneedle-likeTenanorodscrystallinity[16].ThismightbeattributedtothediameterofTenanorodsareuniforminthepresentcase.
4.Conclusions
Insummary,flower-liketelluriumnanocrystalswithuniformbranchesinlargescalewerepreparedthroughasurfactant-assistedmethodusingCTABasthesurfactant.AccordingtoSEMandTEMobservations,theas-obtainedTecrystalsareflower-shaped.BasedonthedeterminationofXRD,HRTEMandEDSanalysis,itwasconfirmedthattheobtainedsamplewasmainlyTeinhexagonalphasewithapreferentialorientationalong[001]direction.Inaddition,RamanspectroscopyperformedononebranchalsoshowsthattheTenanoroddisplayedthreecharacteristicpeaks.TheobtainedTecrystalswithspecialmorphologycanbepotentiallyusefulforthefabricationofnanodeviceswithnovelproperty.
Acknowledgements
ThisworkwassupportedthroughGraduateFoundationofWenzhouUniversity(No.3160603601010724).
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