PREPARATION AND CHARACTERIZATION OF PS-SiO2 NANOCOMPOSITE MICROSPHERES

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Herein,wereportasimple,biomimeticandlow-temperaturemethodforthefabricationofZnOnanostructuressuchasplates,spheres,stars, owersandmultipodsinthepresenceofpoly-vinylpyrrolidone(PVP),usingAu-oligoanilineastheseed.Gold/polyaniline(Au/PANI)asaprecursorhasbeenknowntogivestar-shapedAunanostructures[44].ThoughreportsexistonthesynthesisofAu@ZnOcompositesbysolution-phasemethod[45],noattemptshavebeenreportedtilldateforthesynthesisofZnOofvaryingmorphologiesusingAu-containingseeds.Experimentswerealsoconductedtoseethedifferentshapesobtainedintheabsenceofseedsolutionusingthecommonlyusedbio-friendlytemplate,PVP.Allthenanostructuresattainedwerecharacterizedusingvariousspectroscopicandmicroscopictechniquesandapossiblemechanismfortheformationofthesemorphologiesisproposed.

colorchangedfrompaleyellowtopink,100mLdistilledanilinewasaddedfollowedby500mL25mMHAuCl4.Heatingwascontinuedfor vemoreminutes.Thecolorofthesolutionchangedtolightpinkandablackprecipitatewasformed.Thissolutionwaskeptatroomtemperaturefor5h,centrifugedat4000rpmandtheblackresiduewasdiscarded.Theresultantlightpinksupernatant,whichcontainsoligoaniline-cappedgoldnano-particles,wasusedforfurtherreaction.2.3.SynthesisofZnOnanostructures

Atotalof1mLoftheabove-preparedseedsolutionwasheatedina20mLsamplebottleat601C.Toit,10mLofaqueousPVP(12.5mg/mL)wasaddedwithoutvaryingthetemperature.After30s,1mLofzincacetatewasadded,followedbytheadditionof1mLNaOHofrequiredconcentration,soastomaintainaparticularZn2+:OHÀratio.Heatingwascontinuedfor1htogetaclearsupernatantwithwhiteprecipitateatthebottomofthebottle.Thesupernatantwasremovedandthewhiteprecipitatewaswashedacoupleoftimeswithbothethanolandwater.Finallyitwaskeptfordryingat801Cfor4hinanovenandthewhitepowderthusobtainedwasusedforsubsequentanalysis.TheexperimentwasconductedatdifferentratiosofZn2+:OHÀ,suchas1:0.8,1:1.75,1:3,1:5,1:7.5and1:40togetnano-hexagonalplates,nano-ovalplates,micro-stars,micro- owers,thornsandmulti-pods,respectively.Scheme1givesaschematicofthesyntheticprocedure.

2.4.Instrumentation

Transmissionelectronmicroscopy(TEM)wascarriedoutusingaJEOL3011,300kVinstrumentwithaUHRpolepiece.ThesamplesforTEMwerepreparedbydroppingthedispersiononamorphouscarbon lmssupportedonacoppergridanddriedinambience.Scanningelectronmicroscopic(SEM)imagesweretakeninaHITACHIS-4800FE-SEM.Fortheinfrared

spectra,

2.Experimentalprocess2.1.Materials

AnilinewaspurchasedfromSigmaAldrichanddistilledtwiceunderreducedpressurebeforeuse.Zincacetate((CH3COO)2Zn)andsodiumhydroxide(NaOH)werepurchasedfromRanbaxy.PVPwaspurchasedfromMerck.Tetrachloroauricacidtrihydrate(HAuCl4Á3H2O)waspurchasedfromCDH,India.Allchemicalswereusedassuchwithoutfurtherpuri cation.Triplydistilledwaterwasusedthroughouttheexperiments.Scheme1showstheexperimentalprocedureemployedformakingvariousnanostructuresusingAu/PANIseedsolution.

Synthesisinvolvesthefollowingsteps.2.2.Synthesisofoligoaniline-coatedgoldnanoparticles(AuNPs)Au/PANIhasbeensynthesizedbyaknownproceduredescribedbySajanlaletal.[44].Inatypicalsynthesis,25mgofcitricacidwasdissolvedin35mLofwater.Thesolutionwaskeptat801Cand1mLof25mMHAuCl4wasadded.After10min,whenthe

Scheme1.ProcedureusedforthesynthesisofvariousanisotropiczincoxidenanostructuresusingAu/PANI.