PreparationofSelfStandingPolyanilineBasedMembranes

PreparationofSelf-StandingPolyaniline-BasedMembranes:DopingEffectontheSelectiveIonSeparationandReverseOsmosisPropertiesHu¨seyinDeligo¨zChemicalEngineeringDepartment,IstanbulUniversity,34320Avcılar-Istanbul,TurkeyReceived13November2006;accepted11February2007DOI10.1002/app.26377Publishedonline11May2007inWileyInterScience().ABSTRACT:Theselectiveiontransportofaqueoussaltsolutionsincludingmono-,di-,trivalentcationsacrossbothdopedandundopedpolyaniline(PAni)membraneswasdescribed.PAni-basedasymmetricmembraneswerepre-paredbythephaseinversionmethodfromthecastingsolu-tioncontainingN-methylpyrrolidone.Itwasfoundthatthepermeationrates(PR)declineinthesequenceofPR(NaCl)PR(MgCl2)PR(LaCl3).HCl-dopedPAnimembraneexhibitedhigherpermeationratesforthesaltsthanundopedoneduetoitsmorehydrophilicnature.Inreverseosmosis(RO)applications,itwasobservednowaterpermeationthroughundopedPAniduetolesspermeableandhydropho-bicnature,underevenat40barpressure.ConcerningHCl-dopedPAni,thismembraneshowedverylowwaterflux(Jw)anditwasfoundas1.01Lm
2h
1under40barpressure.Ontheotherhand,theJincreasedlinearlywiththeappliedpressure.Furthermore,typicalseparationfactor(a)valuescal-culatedfrompermeationrateratioswerefoundtobeas6.3and39forNaþ/Mg2þandNaþ/La3þforHCl-dopedPAni,respectively.Especially,HCl-dopedPAnimembranecanbeusedforremovingrare-earthmetalsaltsduetoitshighsepa-rationefficiencyinhightemperatureapplications.
2007WileyPeriodicals,Inc.JApplPolymSci105:2640–2645,2007Keywords:polyaniline;membrane;ionseparation;ionpermeability;reverseosmosisINTRODUCTIONTheuseofpolymersforseparationapplicationshasgrownrapidlyduringthepasttwodecades.1,2Poly-mericmembranesaremainlyusefulinseparationofgases,3,4inorganicionsundernanofiltrationandreverseosmosisconditions,5–7andalcohol/watermixturesunderpervaporationconditions.8Sincethediscoveryofconductingpolymersinthelate1970smanyworkshavebeenpublishedonthecommercialapplicationssuchaselectrochoromicdis-plays,lightweightbatteries,andsensors.9,10Ontheotherhand,someworkshavebeenreportedontheseparationofvariousionorliquidmixturesbyusingtheseconjugatedpolymericmembranes.FirstworkwasreportedbyBurgmayerandMurrayontheuseofelectrochemicallysynthesizedpolypyrroleasan‘‘iongate’’membrane.11Subsequently,FeldheimandElliotreportedastudyontheseparationofneutralsolutesbyusingpoly(3-methylthiophene)andpoly(N-methylpyrrole)-basedconductingpolymersoverporouspolycarbonate(Celgrad)support.12Atthebeginning,interestinpolyaniline(PAni)asama-terialformembraneseparationsystemswasduetoitshighselectivitytowardgases13,14andlateronIllingetal.studiedgasseparationpropertiesofthePAni-basedmembranes.15,16Sincemostliquidsarerareinthesamesizeasgases(2–10A˚)PAnicanbeusedforliquidseparationsaswell.8Recently,pervaporationstudieswithPAnimembraneswerepublishedbyBalletal.8PAnicanbepreparedeitherindopedorundopedstate.Inthedopingprocess,wherecounterionsareaddeduniformlythroughoutthematerialonamolecularlevel,wasfoundtodecreasetheperme-abilityofallgases,whileundopingwasfoundtoincreasegaspermeability.Amongtheconjugatedpoly-mers,PAnihasattractedgreatattentionduetohav-ingdifferentchemicalcharactersandhighthermalstabilityupto4258Cinnitrogen.8Forexample,thedopedformofPAniishydrophilicwhiletheundopedformishydrophobic.Selectiveionseparation,reverseosmosis,andper-vaporationstudiesweremainlycarriedoutbyTiekeandcoworkers.17–19Theyreportedmanyworksoncompositemembranes,whichwerepreparedsuccess-fullythroughlayerbylayer(LBL)technique,17–21showinghighselectiveionpermeationandseparationfactor.Intheseworks,preparingcompositemem-branesconsistingofaverythin,denseseparatinglayerandathickhighlyporousmembranewasdescribedasasuitablemethod.19SeveralstudieshaveshownthattheLBLassemblyofelectrolytesiswellCorrespondenceto:H.Deligo¨z([e-mail]).Contractgrantsponsor:ResearchFundofIstanbulUni-versity;contractgrantnumber:BYPF-7-11/270706.JournalofAppliedPolymerScience,Vol.105,2640–2645(2007)VVC2007WileyPeriodicals,Inc.suitedforthepreparationofcompositemembraneswithanorganized,denseseparationlayerofcon-trolledthicknessinthenanometerrange.Reverse-osmosis(RO)propertiesaromaticpolyam-ide22andpolysulfonemembraneswerereportedear-lierinnanofiltrationapplications.23Duringthelastfewyears,extensiveeffortshavebeenmadetosyn-thesizemembranegradepolymersasaneconomicalsubstituteforthecelluloseacetatewhichisroutinelyusedinthepreparationofmembranesfordesalina-tionintheROtechnique.Withthediscoveryofaro-maticmembranesbyRichterandHoehn,anumberofusefularomaticpolyamide-basedmembraneshavebeendeveloped.24Aromaticpolyamidemembranesbasedonpiperazineshowedhighcompactiononuseathighpressureandshowedasignificantreductioninthesolventflux.Onanalyzingboththeexperimen-taldatareportedintheliteratureandmechanismofthetransportofthesolventthroughthemembranes,ithasbeenconcludedthatthepolymericmaterialwithhydrophilicgroupwouldbeofimprovedqualitytodevelopROmembranes.Intheviewoftheseobser-vations,effortshavebeenmadetopreparepolymericmembranesincludinghydrophilicgroup.However,uptonow,veryfewstudieswerecon-c