改良hummers合成氧化石墨烯

AnimprovedHummersmethodforeco-friendlysynthesisofgrapheneoxide

JiChen,BowenYao,ChunLi,GaoquanShi

*

DepartmentofChemistry,TsinghuaUniversity,Beijing100084,People’sRepublicofChina

ARTICLEINFOABSTRACT

Articlehistory:Received4June2013Accepted21July2013Availableonline27July2013

AnimprovedHummersmethodwithoutusingNaNO3canproducegrapheneoxidenearlythesametothatpreparedbyconventionalHummersmethod.Thismodi cationdoesnotdecreasetheyieldofproduct,eliminatingtheevolutionofNO2/N2O4toxicgassesandsim-plifyingthedisposalofwastewaterbecauseoftheinexistenceofNa+andNO3Àions.Forthe rsttime,wealsodevelopedaprototypemethodofpost-treatingthewastewatercol-lectedfromthesystemsofsynthesizingandpurifyinggrapheneoxide.ThecontentofMn2+ionsinthepuri edwastewaterwasmeasuredtobelowerthantheguidelinevaluefordrinkingwater.

Ó2013ElsevierLtd.Allrightsreserved.

1.Introduction

Graphenehasauniqueatom-thicktwo-dimensionalstruc-ture,excellentelectronic,mechanical,opticalandthermalproperties[1].Therefore,ithasbeenwidelyexploredfortheapplicationsinelectronics[2],catalysis[3],sensors[4],andenergyconversionandstorage[5,6],etc.Forthesepurposes,themass-productionofgraphenematerialsatlowcostsisoneoftheessentialrequirements.Actually,graphenesheetsalreadyexistinnatureandweneedtoexfoliatethemfromtheirprecursors[7].Theexfoliationofgraphitetographenecanberealizedeitherphysicallyorchemically[1].Amongthevariousmethods,chemicalreductionofgrapheneoxide(GO)toreducedgrapheneoxide(rGO)isuniqueandattractivebecauseofitscapabilityofproducingsingle-layergrapheneinlargescaleandatrelativelylowcost[8].Furthermore,GOandrGOareprocessibleandtheycanbefabricatedorself-assem-bledintomacroscopicmaterialswithcontrolledcompositionsandmicrostructuresforpracticalapplications[9].

GOistheprecursorofrGO;thus,itplaysacrucialroleincontrollingthestructure,propertyandtheapplicationpoten-tialofrGO[10À16].ThepioneeringworkonthesynthesisofGOwasreportedbyBrodiein1859[17].Inthismethod,one

equalweightofgraphitewasmixedwiththreeequalweightsofKClO3andreactedinfumingHNO3at60°Cfor4days.Sta-udenmaierimprovedBrodiemethodbyreplacingabouttwothirdsoffumingHNO3withconcentratedH2SO4andaddingKClO3inmultipleportions[18].Thissmallmodi cationen-ablestheoverallreactioninasinglevessel;thussimplifyingthesynthesismethod.However,thisreactionstillneedsalongtimeof4days.ThemostimportantandwidelyappliedmethodforthesynthesisofGOwasdevelopedbyHummersandOffemanin1958(Hummersmethod)[19].Inthiscase,theoxidationofgraphitewasachievedbyharshtreatmentofoneequalweightofgraphitepowdersinaconcentratedH2SO4solutioncontainingthreeequalweightsofKMnO4and0.5equalweightofNaNO3.TheHummersmethod,atleast,hasthreeimportantadvantagesoverprevioustech-niques.First,thereactioncanbecompletedwithinafewhours.Second,KClO3wasreplacedbyKMnO4toimprovethereactionsafety,avoidingtheevolutionofexplosiveClO2.Third,theuseofNaNO3insteadoffumingHNO3eliminatestheformationofacidfog.

Hummersmethodhasbeenpaidthemostintensiveatten-tionbecauseofitshighef ciencyandsatisfyingreactionsafety.However,itstillhasthefollowingtwo aws:(1)theoxi-

*Correspondingauthor:Fax:+861062771149.

E-mailaddress:gshi@http://doc.guandang.net(G.Shi).

0008-6223/$-seefrontmatterÓ2013ElsevierLtd.Allrightsreserved.http://doc.guandang.net/10.1016/j.carbon.2013.07.055

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dationprocedurereleasestoxicgassessuchasNO2andN2O4;(2)theresidualNa+andNO3Àionsaredif culttoberemovedfromthewastewaterformedfromtheprocessesofsynthe-sizingandpurifyingGO.Tourandco-workersimprovedtheHummersmethodbyexcludingNaNO3,increasingtheamountofKMnO4,andperformingthereactionina9:1(byvolume)mixtureofH2SO4/H3PO4[20].Thismodi cationissuccessfulinincreasingthereactionyieldandreducingtoxicgasevolution,whileusingtwiceasmuchKMnO4and5.2timesasmuchH2SO4asthoserequiredbyHummersmethodandalsointroducinganewcomponentofH3PO4tothereactionsystem.

Recently,Baek’sgroupstudiedtheprocessofetchingthebasalplanesofhighlyorderedpyrolyticgraphite(HOPG)withahotmixtureofH2SO4andHNO3[21].Inthiscase,thegraph-enelayersofHOPGwereeffectivelycutandexfoliatedafteralong-termtreatment.ThisobservationindicatesthattheH2SO4/HNO3mixtureusedinHummersmethodactsasachemical‘‘scissor’’andachemical‘‘drill’’forgrapheneplanestofacilitatethepenetrationofoxidationsolution.Ontheotherhand,KMnO4isoneofthestrongestoxidants,espe-ciallyinacidicmedia[22].WiththeassistanceofKMnO4,acompleteintercalationofgraphitewithconcentratedH2SO4canbeachieved,forminggraphitebisulfateinwhicheverysingle-layergrapheneissandwichedbythelayersofbisulfateions[23,24].ThiscompleteintercalationensurestheeffectivepenetrationofKMnO4solutionintographenelayersfortheoxidationofgraphite.Accordingly,KMnO4canalsotaketheroleofNaNO3andthelatterisunnecessaryforthesynthesisofGOusingHummersmethod.Inthisarticle,wedemon-stratethatGOcanbeproducedusinganimprovedHummersmethodwithoutusingNaNO3.ThismethoddecreasesthecostandenvironmentaldutyofGOproduction.

2.

Experimental

2.1.

Synthesisandpuri cationofGO

GOwaspreparedbytheoxidationofnaturalgraphitepowder(325mesh,QingdaoHuataiLubricantSealingS&TCo.Ltd.,Qingdao,China)accordingtoHummersmethodwithamodi- cationofremovingNaNO3fromthereactionformula[19].Typically,graphitepowder(3.0g)wasaddedtoconcentratedH2SO4(70mL)understirringinanicebath.Undervigorousagitation,KMnO4(9.0g)wasaddedslowlytokeepthetemper-atureofthesuspensionlowerthan20°C.Successively,thereactionsystemwastransferredtoa40°Coilbathandvigor-ouslystirredforabout0.5h.Then,150mLwaterwasadded,andthesolutionwasstirredfor15minat95°C.Additional500mLwaterwasaddedandfollowedbyaslowadditionof15mLH2O2(30%),turningthecolorofthesolutionfromdarkbrowntoyellow.Themixturewas lteredandwashedwith1:10HClaqueoussolution(250mL)toremovemetalions.Theresultingsolidwasdriedinairanddilutedto600mL,makingagraphiteoxideaqueousdispersion.Finally,itwaspuri edbydialysisforoneweekusingadialysismembrane …… 此处隐藏：14385字，全部文档内容请下载后查看。喜欢就下载吧 ……