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Matrixeffectofmixed-matrixmembranecontainingCO2-selectiveMOFsJiyoungKim,1JiyoungChoi,1YongSooKang,2JongokWon11DepartmentofChemistry,SejongPolymerResearchCenter,SejongUniversity,209,Neungdong-Ro,Gwangjin-Gu,Seoul143-747,Korea2DepartmentofEnergyEngineering,HanyangUniversity,222Wangsimni-Ro,Seongdong-Gu,Seoul133-791,KoreaCorrespondenceto:J.Won(E-mail:jwon@sejong.ac.kr)ABSTRACT:Facilitatedmixed-matrixmembranes(MMMs)containingCu-metalorganicframeworks(Cu-MOFs)withhighCO2selec-tivityonanasymmetricpolysulfonesupportwerefabricatedandexaminedtheeffectofgasseparationperformanceusingdifferentmatrices.Anamorphouspoly(2-ethyl-2-oxazoline)(POZ)andsemicrystallinepoly(amide-6-b-ethyleneoxide)(PEBAXVRMH1657)blockcopolymerwerechosenasthepolymericmatrixandtheeffectofthematrixonCO2separationforMMMscontainingCu-MOFswasinvestigated.TheinteractionofCO2indifferentmatrixwasinvestigatedtheoreticallyusingthedensityfunctionaltheorymethod,anditwasfoundthattheamidesegmentinPEBAXwouldcontributemoretotheCO2solubilitythanethersegment.Themorphologicalchangeswereinvestigatedbydifferentialscanningcalorimetry,fieldemissionscanningelectronmicroscopeandX-raydiffractometer.TheidealselectivityofCO2/N2wasenhancedsignificantlywiththeadditionofaCu-MOF,andthevaluesarehigherintheCu-MOF/PEBAXMMMcomparedwiththatinaPOZbasedasymmetricMMM.ImprovementintheCO2/N2selectivityofaCu-MOF/PEBAXMMMwasachievedviafacilitatedtransportbytheCO2-selectiveCu-MOFsduetoboththeirhighadsorptionselec-tivityofCO2overN2andthedecreasedcrystallinityofPEBAXduetothepresenceoftheCu-MOFs,whichwouldprovideasynergiceffectontheCO2separation.VC2015WileyPeriodicals,Inc.J.Appl.Polym.Sci.2016,133,42853.KEYWORDS:applications;membranes;porousmaterials;separationtechniques;structure–propertyrelationsReceived17June2015;accepted20August2015DOI:10.1002/app.42853INTRODUCTIONApolymericseparationmembraneisconsideredtobeaneffec-tiveapproachfortheseparationofgaseousmixturesduetothehighseparationefficiencyandlowoperationcostcomparedwithconventionalseparationmethods.1–4Howevermostofthepolymericmembranessufferfromthetrade-offbetweenthepermeabilityandtheselectivity;5theselectivitydecreaseswithincreasingpermeability.Thistrade-offinmembraneperform-ancecanbeovercomebyadoptingfacilitatedtransportusingaselectiveCO2carrier,andonecandidateforthecarrierisCO2-selectivemetal-organicframeworks(MOFs).Becausetheperme-abilityandselectivitypropertiescanbemanipulatedinMOFsbythecombinationofmetalionsandorganiclinkersduringsynthesis,itispossibletoapplyfunctionalsitesthathaveaninteractionbetweentheMOFandCO2.IftheinteractionbetweentheMOFandCO2couldbeoptimized,facilitatedtransportmembranesthatcontainagas-selectiveMOFcarrierwouldcircumventthetrade-off.WiththedevelopmentoftremendousnanoporousMOFs,sev-eralmixed-matrixmembranes(MMMs)thatcontainananopo-rousMOFsinapolymermatrixhaverecentlybeenreported.6–15However,mostofstudiesarefocusedonthehighporosityandstructuralselectivityofMOFs,whichexhibitamolecularsievingabilitywithhighpermeability,ratherthantheselectivity.ToadoptanadvantageofporousMOFsintothefacilitatedtransportmembrane,ahighselectivityofCO2andreversibleinteractionsbetweenCO2andtheporeoftheMOFsarenecessary.WethereforepreparedtheCO2-selectiveMOFs,[{Cu2(Glu)2(l-bpa)}�(CH3CN)]nwherebpa51,2-bis(4-pyri-dyl)ethane(Cu-MOFs),16whichhavearelativelyhighselectivitytowardsCO2overN2atroomtemperature.ThechoiceofthematrixpolymerisimportanttofabricateMMMscontainingCu-MOFs.AlthoughmatchingtheMOFtothepolymericmatrixisconsideredrelativelyeasythantheonebasedonzeolitebecauseofthepartiallyorganicsegmentoftheMOFs,itisstilldifficulttoobtainaperfectmatchbetweenthepolymermatrixandtheMOFforthepreparationofdefect-freeMMMs.Ifthereareanon-selectivevoidsresultingfromtheincompatibilitybetweenMOFmaterialsandthepolymermatrixattheirinterfaceandtheporesarelargeenoughforgasmole-culestodiffusethroughthem,theoverallselectivityofthemembranewillbereduced.VC2015WileyPeriodicals,Inc.:10.1002/APP.4285342853(1of8)ThereareseveralsurfacemodificationapproachestoenhancetheinterfacialadhesionbetweentheMOFandthepolymermatrix,14,17theresultingMMMsstillsufferfromlowcompati-bilitybetweenthesecomponents,andmostofthemembraneexhibitsimprovedpermeabilityratherthanselectivity.RecentlypreparationofMOF-MMMsbyusingparticlefusionofpolymerparticlesandthein-situsynthesizedMOFparticles.18Nottomentionofthesemodificationstepsaddtothecostandcom-plexityofmembranefabricationandmakesuchMMMslesscompetitive.17,19Asonewaytosolvethisproblem,wefocusedontheapplica-tionofaCO2-selectiveMOFasacarrierforthefacilitatedtransportmembrane.IftheinteractionsbetweentheMOFandCO2arehighenoughandreversiblefortheactionoftheCO2carrier,thenitispossibletofabricatethehighlyselectiveasym-metricMMM,despitethepoorstructuralselectivityresultingfromtheinterfacialvoidbetweenthepolymermatrixandtheMOF.Previously,twodifferentgas-selectivemicro-sizedframe-worksweresynthesizedanddispersedinpolyoxazoline(POZ),asamatrixforthefabricationoffacilitatedMMM.20ItwasfoundthattheCO2/N2selectivit