关于石墨烯的英文文献

LetterstotheEditorSize-controlledsynthesisofgrapheneoxidesheetsonalargescaleusingchemicalexfoliationLongZhang,JiajieLiang,YiHuang,YanfengMa,YanWang,YongshengChen*KeyLaboratoryofFunctionalPolymerMaterials,CenterforNanoscaleScienceandTechnology,InstituteofPolymerChemistry,CollegeofChemistry,NankaiUniversity,WenjinRd.94,Tianjin300071,ChinaARTICLEINFOArticlehistory:Received12June2009Accepted19July2009Availableonline23July2009ABSTRACTThesynthesisofgrapheneoxide(GO)sheetswithcontrolledsizeonalargescalewasdevel-opedusingchemicalexfoliationbysimplycontrollingtheoxidationandexfoliationproce-dure.TheGOsamplespreparedunderdifferentconditions,whichallhaveexcellentwaterdispersion,arecharacterizedbythermalgravimetricanalysis,Ultraviolet–visiblespectros-copy,X-raydiffractionandatomicforcemicroscopy.Itisfoundthataslongeroxidationtimesandmoreoxidantsareused,themeansizeoftheGOsheets,whichhasaGaussiandistribution,decreasesfrom59,000to550nm2.2009ElsevierLtd.Allrightsreserved.Graphene,withone-atom-thicktwo-dimensionalindivid-ualsheetstructurecomposedofsp2-hybridizedcarbon,hasdrawnagreatdealofattentionduetoitsremarkableelec-tronic,thermalandmechanicalproperties[1].Researchongrapheneisoriginallymotivatedbyitsgreatpromiseforfu-turetechnologicalapplicationsinmanyfields,suchashighlyconductingcomposite[2]andothermicrotonano-scaleelec-tronicdevices[3].Itisclearthatthepropertiesofgraphenestronglydependonitsuniquestructureandmorphology.Forexample,thesizeofgrapheneplaysanimportantroleintheirconductivities[4].Accordingly,itishighlydemandedtodevelopsimpleandefficientmethodsfortheproductionofgraphenesheetswithcontrolledsizeandlargequantitiesfortheirbroadrangeofapplications.Currently,micromechanicalcleavage[5],epitaxialgrowthonsiliconcarbide[6]andchemicalexfoliation[2,7]havebeenusedwidelytopreparegraphenesheets.Comparedtothefirsttwomethods,thechemicalexfoliationmethodisconsideredtobethemosteffectiveandeconomicalwaytopreparegraphenesheetsinlargequantityfrombulkgraphite[8],inwhichaprocessofgrapheneoxide(GO)sheetsisinvolved[2,8].Importantly,thearomaticnetworkandtheintrinsicpropertiesofgraphenecanbemostrestoredthroughtheremovalofthefunctionalgroupsbyeitherchemicalreductionorthermalannealingforGO.Recentlyasimpleandeffectivestrategytotunethenumberofgraphenelayersbyselectingsuitablestartinggraphitematerialshasbeenpresentedusingdifferentgraphitematerials[9].However,thelargescaleproductionofhigh-qualitygraphenewithcontrolledsizestillremainsasignificantchallenge.Itiswellknownthattheoccurrenceoffaultlinesandcracksingraphite,whichleadstounzippingofgraphitelat-tice,aredirectlyrelatedtotheoxidationprocess[10].Herein,wehavestudiedtheeffectofoxidationtimeandtheamountofoxidantsonthesizecontrollingofGOsheetsbychemicalexfoliation.GOsheetswithdifferentsize,namelyGO-1,GO-2,GO-3andGO-4,werepreparedusingthemodifiedHum-mersmethodfromflakegraphite,whereGO1–4refertotheproductswithprogressiveoxidationsteps(seeSupplemen-tarymaterial)andhavestatisticalmeansizesof59,000,22,000,3500and550nm2,respectively.Thuswithincreasingreactiontimeandoxidants,themeansizesofGOsheets,whichexhibitGaussiandistribution,showaregulardecreaseintheorderfromGO-1toGO-4,andthemaximumdistribu-0008-6223/$-seefrontmatter2009ElsevierLtd.Allrightsreserved.doi:10.1016/j.carbon.2009.07.045*Correspondingauthor:Fax:[phone].E-mailaddress:[e-mail](Y.Chen).CARBON47(2009)3365–3380availableat(TGA)resultsofalltheGOsamplesshowamajormasslossofmorethan30%intherangeof110–230C(Fig.1a),correspondingtotheremovaloflabileoxygen-containinggroups.However,GOsamplestreatedforlongeroxidationtimeandmoreoxidantsshowafastermasslossfrom110to230C,illustratingalowerther-malstabilityandmorefunctionalgroups.DecompositiontemperatureofGO-1,GO-2,GO-3andGO-4obtainedfromTGAcurvesare198C,196C,183Cand180C,respectively,suggestingthedecreaseofthermalstabilityfromGO-1toGO-4.Differentialscanningcalorimetry(DSC)curvesofGO-1,GO-2,GO-3andGO-4showthecorrelateddegradationpeakscentered216C,213C,196Cand190C,respectively(Fig.1b).ThisphenomenonisprincipallyascribedthatmoreoxidationandlongerexfoliationintroducemoredefectsandfunctionalgroupsontheGOsheets,whichreducesthesizeoftheGOsheetswithmorefunctionalgroupsandthuslowersdecompositiontemperature[8,10].Ultraviolet–visible(UV–vis)spectroscopymeasurementswereemployedtomonitorthedegreeofoxidationoftheGOsheets.TheabsorptionpeaksofGO-1,GO-2,GO-3andGO-4are226,222,220and217nm,respectively(Fig.2a),indicatingahypochromaticshiftoftheabsorptionpeakswhichismainlybecausethesizeofp-conjugationsystemgraduallydecreaseswithincreasingdegreeofoxidation.Duetothehydrophilicnatureoftheoxygenatedgraphenelayers,GOcanreadilybeexfoliatedinwaterandformastablecolloidalsuspensionofindividualGOsheets[8]underamildultrasonictreatment.Asanexampleforthisexcellentdispersion,theabsorbanceofGO-4aqueoussolutionswaswellinlinewiththerelativeconcentrations(insetinFig.2b),obe