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

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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@(G.Shi).

0008-6223/$-seefrontmatterÓ2013ElsevierLtd.Allrightsreserved./10.1016/j.carbon.2013.07.055