EnhancedCO2N2separationbyporousreducedgrapheneoxid

EnhancedCO2/N2separationbyporousreducedgrapheneoxide/PebaxmixedmatrixmembranesGuanyingDonga,JingweiHoub,JingWanga,c,YataoZhanga,n,VickiChenb,JindunLiuaaSchoolofChemicalEngineeringandEnergy,ZhengzhouUniversity,Zhengzhou450001,ChinabUNESCOCentreforMembraneScienceandTechnology,SchoolofChemicalEngineering,UniversityofNewSouthWales,Sydney,AustraliacDepartmentofChemicalEngineering,KULeuven,Celestijnenlaan200F,B-3001Heverlee,BelgiumarticleinfoArticlehistory:Received10June2016Receivedinrevisedform26August2016Accepted26August2016Availableonline28August2016Keywords:PorousreducedgrapheneoxidePebaxs1657MixedmatrixmembraneCO2captureabstractComputationalsimulationshavesuggestedtheenormouspotentialofusingporousgraphene-basedmaterialsforgasseparation.However,thishasyettobedemonstratedinacontinuousandmacroscopicmembraneduetothedifficultyinmembranefabrication.Inthiswork,wereportedafacileprocesstofabricatethepartiallyporousreducedgrapheneoxide(PRG)nanosheetsfromgrapheneoxide(GO)viaawetchemicalprocess.ThenthefabricatedPRGwasblendedintoPebaxs1657polymertoprepareamixedmatrixgasseparationmembrane.InordertoensuregooddispersionofthePRGnanosheetswithinthepolymericmatrix,thereductiondegreeofGOshouldbecarefullycontrolled.Inaddition,theresidualfunctionalgroupsonthepartiallyreducednanosheetssurfacefacilitatedtheformationofhighlyefficientmolecularsievinglaminatestructureswithinthemixedmatrixmembrane:thenarrowgasflowgalleries(averagewidthof0.34nm)betweentheneighbouringnanosheetsensuredeffectivemolecularsievingofCO2againstotherlargergasmolecules,whilethemesoscopicporesonthelaminateprovidedrapidgastransportpathways.Finally,themixedmatrixgasseparationmembranehadsubstantiallyimprovedCO2permeabilityaswellasCO2/N2selectivity.ThisworkisthefirsttoreportthefabricationoftheporousGO-basedgasseparationmembrane,andoffersmanyopportunitiestoexploittheuniquepropertiesofporousGOinthefabricationofvariousmolecularsievingmembranes.&2016ElsevierB.V.Allrightsreserved.1.IntroductionPolymericmembrane-basedgasseparationhasexperiencedamajorexpansionduringthepastfewdecades.Ithasgreatpoten-tialingreenhousegascapture,naturalgassweeteningandhy-drogenpurification[1–3].Theperformanceofthemembraneismainlydeterminedbyitsintrinsicmaterialproperties.Despitegreateffortshavebeendevotedtodevelopingnewpolymericmaterials,theperformanceofthemembranerarelyexceedsthepermeabilityandselectivitytrade-off(theRobesonupperbound)[4].Ontheotherhand,outstandinggasseparationperformanceisobservedwiththeinorganicmembranes[5].However,thediffi-cultyintheirfabricationandthehighcostlimittheirwideap-plication.Asaresult,thecurrentresearchfocusistointegrateinorganicnanofillersintopolymericmembranesviaeitherblendingorsurfacecoating,inordertocombinetheadvantagesofbothpolymericandinorganicmaterials[6].Themostcommonlyappliedinorganicmaterialsincludezeolites,carbonmolecularsieves,metalorganicframeworks,carbonnanotubes,andgra-phene-basedmaterials[7–9].Theemerginggraphene-basedmaterials,suchasgrapheneandgrapheneoxide(GO),haveattractedextensiveattentionbecauseoftheirexceptionalmechanicalstrength,chemicaltunability,cost-effectiveproductionanduniquetwo-dimensionalstructure[10,11].ThepreviousresearchhasfoundthattheindividualGOnanosheetsarecompletelyimpermeabletoliquidandgases,duetothehighelectrondensityofthearomaticringsonthena-nosheets[12].Asaresult,themainseparationmechanismfortheGO-basedgasandwaterseparationmembranesisbasedontheformationofthemolecularsievinggalleriesbetweentheneigh-bouringnanosheetsorpossibledefectsonthenanosheets[13–19].Furthermore,theseparationofdifferentsizedgasmoleculescanberealizedbycontrollingthelaminatestackedstructure[20].Sofar,GO-polymergasseparationmembraneshavebeenfabricatedviablending,interfacialpolymerizationorsurfacecoating[21–24].However,themainproblemforGO-polymermembranesistherelativelylowgaspermeability,whichpartlyarisesfromthesub-stantialresistanceofmicroporoussubstrates[22].Inaddition,theincorporationofthenonporousGOincreasesthemasstransferContentslistsavailableatScienceDirectjournalhomepage:://dx.doi.org/10.1016/j.memsci.2016.08.0590376-7388/&2016ElsevierB.V.Allrightsreserved.nCorrespondingauthor.E-mailaddress:[e-mail](Y.Zhang).JournalofMembraneScience520(2016)860–868resistancethroughthewholemembrane.Inanotherwords,theintrinsicbarrierpropertyofGOcanleadtothereducedperme-abilitywhenthegastransportisdominatedbylong,tortuouspathwayscreatedbytheGOinterlayers,asreportedinourpre-viouswork[23].Somerecentresearcheshaveincorporatedna-nomaterialsincludingCNTsandMOFsintothepolymer-GOcom-positemembranestoimprovethegaspermeabilityandselectivity[25–27].Ontheotherhand,thepresenceofsurfacefunctionalgroupsonGOcanprovidegreatpotentialforfurthermodificationtointroduceefficientgastransportpathways[28–30].Besides,thisproblemcanalsobepotentiallymitigatedbydrillingnanosizedporesonthemono-atomicgraphenesheets.Theporesonthegraphenenanosheetscanbeintroducedbyhigh-energyradiation(e.g.oxidativeetchingoroxygen-plasmaetching).Theporousgrap