Enhancementonthepermeationperformanceofpolyimidemi

EnhancementonthepermeationperformanceofpolyimidemixedmatrixmembranesbyincorporationofgrapheneoxidewithdifferentoxidationdegreesLiZhao,ChengCheng,Yu-FeiChen,TingWang,Chun-HuiDuandLi-GuangWu*Grapheneoxide(GO)withdifferentoxidationdegreesweresynthesizedbyharshoxidationofgraphiteusingtheimprovedHummersmethod.TheGO/polyimide(PI)mixedmatrixmembranewassuccessfullyfabricatedbyinsitupolymerizationofPImonomers(3,3′,4,4′-biphenyltetracarboxylicdianhydrideand4,4′-diaminodiphenylether)withGO.ThestructureofGOwascharacterizedbyFouriertransforminfrared,transmissionelectronmicroscopy,atomicforcemicroscopy,X-raydiffraction,andthermalgravimetricanalysis–differentialthermalanalysis.TheperformanceofdifferentGO/PImixedmatrixmembraneswasevaluatedbypermeationexperimentsofCO2/N2gasmixture(volumeratio,1:9).ResultsshowedthatmorepolarfunctionalgroupswereintroducedtoGOwiththeincreaseinoxidationdegreeofGOinthepreparationprocess,producingfewerlayersandmoretranslucentstructures.GOwithhigheroxidationdegreehassignificanteffectonitsdispersionintheN,N-dimethylacetamidesolventandpolymermatrixmaterials.ThepermeabilityofGO/PIhybridmembranesforCO2andN2increased.TheCO2/N2permeationselectivityofmembranesexhibitedatrendofinitialincrease,followedbyadecrease,withtheincreaseinoxidationdegree,whenthesameamountofGOwasadded.ForGOwiththesameoxidationdegree,thepermeabilityandpermeationselectivityofhybridmembraneinitiallyincreased,andthendecreasedwiththeadditioncontentofGO.Inthecaseofhybridmembranecontaining1wt%monolayerGO,themaximumpermeabilityandpermeationselectivityofhybridmembranesforCO2were14.3and4.2timesmorethanthatofPImembranewithoutGO,respec-tively.Copyright©2015JohnWiley&Sons,Ltd.Keywords:grapheneoxide;polyimide;insitupolymerization;mixedmatrixmembrane;gaspermeationINTRODUCTIONSeparationofCO2fromnaturalgasandfluegasesplaysanim-portantroleinthefieldofglobalenvironmentprotection.Mem-braneseparationisanovelandenergy-savingtechnologyforseparatingCO2incomparisonwithconventionalamineabsorp-tionsystem.[1]Polymermembrane,especiallythepolyimide(PI)membrane,hasbeenextensivelystudiedasoneofthepotentialmaterials[2–4]becauseofitsdesirablegaspermeationselectivityandgoodmechanicalproperty.However,thelowCO2perme-abilityofthePImembranelimitsitsapplicationintheseparationofCO2.Currently,thedevelopmentoforganic–inorganichybridmembranesprovidesanewdirectiontosolvethisissue.ThegaspermeationperformanceofPImembranescanbeimprovedbyincorporatinginorganicnanomaterialsintothepolymericma-trix.InthestudyofNiketal.,[5]anewkindofzeolitewassynthe-sizedandthenincorporatedintoas-synthesized6FDA-ODAPIpolymermatrixtoobtainanorganic–inorganiccompositemem-braneafterpyrolysis.TheynoticedthattheadditionofzeoliteparticlesinthePImatrixcaused4.3timesenhancementinCO2permeability.Rafiqetal.[6]fabricatedanorganic–inorganichy-bridmembranefromsilicananoparticlesandpolysulfone/PIbysolutionblendmethod,inwhichthesilicasolwaspreparedbyhydrolyzingtetraethylorthosilicateinethanolinthepresenceofhydrogenchloride(HCl)catalyst.Theresultshowsthattheadditionofsilica,withupto20%content,increasedtheCO2gaspermeationofpolysulfone/PIhybridmembraneto240%.Amongmanyinorganicnanomaterials,carbonnanotubeandgrapheneasnovelcarbonnanomaterialsareinterestingcompositefilmmaterialsbecauseoftheiruniquestructureandoutstandingelectronicandchemicalstabilities.Inparticular,graphenehasbeenextensivelystudiedingasseparationsinceitssuccessfulisolationin2004[7]becauseofitsextremelylargesurface-to-volumeratio,strongadsorptionpropertiesforgas,andmechanicalstrength.[8,9]Theseuniquepropertiesmakegraphene,includinggrapheneoxide(GO),apromisinginorganicnanomaterialforCO2separationmembranes.Schrier[10]usedmolecularsimulationstoinvestigatetheadsorptioneffectofCH4,CO2,N2,O2,H2S,SO2,andH2Oingraphenesurface.There-sultsshowedthatgraphenewassuitableforCO2captureandseparation.Burressetal.[11]functionalizedGOwithboricacidtoformanewGOskeletonmaterial.Theyobservedthatthistype*Correspondenceto:Li-guangWu,SchoolofEnvironmentalScienceandEngineering,ZhejiangGongshangUniversity,Hangzhou310012,China.E-mail:[e-mail],C.Cheng,Y.-F.Chen,T.Wang,C.-H.Du,L.-G.WuSchoolofEnvironmentalScienceandEngineering,ZhejiangGongshangUniversity,Hangzhou310012,ChinaResearcharticleReceived:17October2014,Revised:12December2014,Accepted:17December2014,PublishedonlineinWileyOnlineLibrary:6February2015(wileyonlinelibrary.com)DOI:10.1002/pat.3456Polym.Adv.Technol.2015,26330–337Copyright©2015JohnWiley&Sons,Ltd.330ofmaterialcouldexhibittheinterestinggassorptionpropertiesofCO2.TheresultsfromLee’sworkshowedthatagraphenemembranecouldefficientlyseparateCO2fromCO2/O2,CO2/N2,andCO2/CH4mixturesbecauseitssingle-atomthickstructureprovidedfastertransportandhigherselectivityofgasmoleculescomparedwiththecarbonnanotube.[12]Inadditiontothechar-acteristicsofthenanomaterialadded,theaffinitybetweennanomaterialsandpolymermembranesubstratesisalsoakeyfactor,whichdeterminesthegasseparationperformanceofhy-bridmembranes.Inourpreviouswork,[13]weobservedthatthecommonmembranesubstratesforgasseparationhad