Green chemical approaches to ZnSe quantum dots preparation,

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Journal of Experimental NanosciencePublication details, including instructions for authors and subscription information:http://www.informaworld.com/smpp/title~content=t716100757Green chemical approaches to ZnSe quantum dots: preparation,characterisation and formation mechanismLanlan Chena; Yang Jianga; Chun Wanga; Xinmei Liua; Yan Chena; Jiansheng Jieba School of Materials Science and Engineering, Hefei University of Technology, Hefei, Anhui 230009,PR China b Department of Applied Physics, Hefei University of Technology, Hefei, Anhui 230009, PRChinaOnline publication date: 24 March 2010

To cite this Article Chen, Lanlan , Jiang, Yang , Wang, Chun , Liu, Xinmei , Chen, Yan and Jie, Jiansheng(2010) 'Greenchemical approaches to ZnSe quantum dots: preparation, characterisation and formation mechanism', Journal ofExperimental Nanoscience, 5: 2, 106 — 117To link to this Article: DOI: 10.1080/17458080903314022URL: http://dx.doi.org/10.1080/17458080903314022

Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdfThis article may be used for research, teaching and private study purposes. Any substantial orsystematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply ordistribution in any form to anyone is expressly forbidden.The publisher does not give any warranty express or implied or make any representation that the contentswill be complete or accurate or up to date. The accuracy of any instructions, formulae and drug dosesshould be independently verified with primary sources. The publisher shall not be liable for any loss,actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directlyor indirectly in connection with or arising out of the use of this material.JournalofExperimentalNanoscienceVol.5,No.2,April2010,106–117

GreenchemicalapproachestoZnSequantumdots:preparation,characterisationandformationmechanismLanlanChena,YangJianga*,ChunWanga,XinmeiLiua,YanChenaandJianshengJiebaSchoolofMaterialsScienceandEngineering,HefeiUniversityofTechnology,TunxiRoad193,Hefei,Anhui230009,PRChina;bDepartmentofAppliedPhysics,HefeiUniversityofTechnology,Hefei,Anhui230009,PRChina(Received13April2009;finalversionreceived6September2009)ZnSequantumdots(QDs)andflower-shapednanocrystals(NCs)weresuccess-fullysynthesisedviaacheap,greenandnontoxicroute,usingenvironmentallyfriendlyN,N-dimethyl-oleoylamideasthesolventofSe.Theexperimentalresultsshowthattheas-preparedZnSeQDswithazinc-blendestructurehaveanarrowsizedistributionandwithoutresortingtoanyas-syntheticsize-selectiveprocedure.AsystematicstudyoftheZnSeQDsformationprocessindicatesthefollowingproperties:variationofsomereactionparametersallowsustotunetheparticlesizesandplaysagreaterroleinthedeterminationofthemonodispersecharacterisation,forexample,theseparametersincludetheamountofligandandprecursors,theinjectiontemperatureofSesolution.Thesesizetunabilitiesinterpretedwellbythegrowthkinetics.AnotherinterestingresultisthattheZnSeQDsaggregatetoflower-shapedNCs,andtheflower-shapedNCsalsohavesize-dependencequantumeffectsastheprepareddisperseZnSeQDs.Keywords:ZnSe;quantumdots;greenchemistry;II–VIgroupsemiconductors1.IntroductionSynthesisofsemiconductorquantumdots(QDs)ornanocrystals(NCs)bymeansofpyrolysisinhotsurfactantmixtureshasevolvedoverthepast10yearstoproduceavarietyofhighqualitymaterialsincolloidalsolutionsrangingfromII–VINCs,forexample,CdS,CdSe,CdTe,HgTe,[1–6]ZnS,ZnSeandZnTe,[7–9]toIII–V,forexample,InAsandInP,[6,10]andII–VI,forexample,PbSandPbSe,[11,12]QDs.SemiconductorQDsareofgreatinterestforbothfundamentalresearchandindustrialapplications,suchasbiomedicaltag[13,14],lightemittingdiodes[15,16],laser[17,18]andsolarcells[19].MostoftheinterestisfocussedonCdSeQDs,becausetheiropticalspectracanbemadetocoverthewholevisiblerangebysimplytuningtheirparticlessize[20,21].Thehighlytoxiccomponentcadmium,however,placesCdSeQDsinadisadvantageouspositionoreveninadoubtfulfuture.CadmiumcouldbereleasedfromCdSeNCs.Anyleakageofcadmiumwouldbefataltobiologicalsystems,andeventuallycadmiumcontainingproductswould

*Correspondingauthor.Email:apjiang@hfut.edu.cnISSN1745–8080print/ISSN1745–8099onlineß2010Taylor&FrancisDOI:10.1080/17458080903314022http://www.informaworld.comDownloaded At: 14:52 4 September 2010causeenvironmentalproblems[22–24].Therefore,attemptstodevelopnoncadmiumsubstitutesarecurrentlythepriorityinthisfield.ZnSe,animportantII–VIsemiconductor,hasattractedconsiderableattentionforapplicationsinphotodetectors,andfull-colourdisplays[25,26].Additionally,ZnSehassignificantlylargeexcitonbindingenergy(21meV)[27],whichmakesitanidealcandidateforefficientroom-temperatureexcitondeviceswithimprovedtemperaturecharacteristics[28].Severalnovelapplicationshavebeenpresented,whichrequiresize,shapeandphasecontrolofZnSenanostructuredmaterials[29,30].Recently,PradhanandPeng[31]developedthesynthesisofMn-dopedZnSeQDswithavisibleemittingwindowof470–590nm.ThiswouldultimatelyeliminatethetoxiccomponentsandmakeZnSeNCsanidealsubstituteofCdSeNCs.However,thissyntheticapproachandthepreviousonesinvolvedtheuseoftoxicandexpensivestartingmaterial,suchastrioctylphosphine(TOP)andtributylphosphine(TBP).Fortheenvironmentalfriendlyaims,moreandmoreresearchersareintegratinggreenerchemistryprinciplesintotheirsyntheticapproachesforgreenernanoproducts.Aphosphine-freeapproachwasintroducedfortheformationofhighqualityCdSQDsbyusingoleicacid(OA)andoctadeceneastheligandandthenoncoordinatingsolvent,respectively[32].Thisapproachisquitegeneralandwasemployedforthesynthesisofmanyothernanomaterials[33],includingZnSe[34].InthecaseofZnSe,phosphineswereneededtodissolveSepowderandcouldnotbeeliminated.Recently,ourgroupreportedthatSecouldbedissolvedinN,N-dimethyl-oleoylamide(DMOA)atmildtemperatures,whereCdSeQDsweresynthesised[35].However,agreenerroutetoZnSeQDsstillhaschallenges.Here,wereportonacheaper,greener,phosphine-freerouteforpreparationofZnSeQDswithN,N-DMOAasasolventtodissolveSepowder,whicheliminatestheneedforair-sensitive,toxicandexpensivechemicalTOP,andusesnaturalsurfactantOAtodissolvezincacetateandformzincoleatesolutioninthenoncoordinatingsolvent.ThepossiblemechanismofchemicalreactionsinoursystemleadingtotheZnSenanoparticleformationwasproposed.Anotherinterestingresultisthattheflower-shapedNCswhichwereformedbyZnSeQDsalsoshowsize-dependencequantumeffects.

2.Experimental2.1.SynthesisZnSeQDsweresynthesisedinathree-neckflaskequippedwithacondenser,magneticofstirrer,thermocoupleandheatingmantle.Afixedamountofzincacetate(99.99%,Zn(CH3COO)2)wasaddedintoOA(fromtheSinopharmChemicalReagentCo.,Ltd,C18H34O2)and1-octadecene(ODE,90%,fromAcros,C18H36)ina25mlthree-neckflask.Themixturewasdegassedat120󰀂C,thenwasheatedto290󰀂CunderArfloworairatmosphereinlessthan5min.SaturatedSestocksolutioninN,N-DMOA(C22H41NO2)wasobtainedbydissolvingSepowder(99.99%,100mesh)inDMOA.Thenseleniumsolutionwasinjectedintothehotmixture.Aftertheinjection,thetemperaturewasdroppedto270󰀂CforthegrowthofZnSenanoparticlesandcontinuedfor2mintogetalightyellowsolution.Atdifferentreactiontimeintervals,aliquotsweretakenfromtheflask;andtheneachaliquotwasimmediatelycooledtoroomtemperaturetoquenchthereactionbymixingitwithabout2mlofcoldtoluene.TheZnSeQDswereprecipitatedbyaddingmethanolintothetoluenesolutionandwerefurtherseparatedandpurifiedbyrepeatedcentrifugationanddecantation.ThepurifiednanoparticlesredispersedintolueneJournalofExperimentalNanoscience107

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