非荷电膜表面离子吸附对其等电点和渗透性能的影响

非荷电膜表面离子吸附对其等电点和渗透性能的影响鲍文,许振良＊,杨　虎(,,200237)　:为考察电解质溶液中不同离子在膜表面的吸附作用,采用自制的截留相对分子质量40000的PVDF中空纤维超滤膜进行电性能和渗透性能表征.由于PVDF无可离子化基团或固有电荷,可大大简化模型,因而考察了膜在1mmol/L四种不同类型电解质(阴阳离子价态)KCl(1∶1),K2SO4(1∶2),MgCl2(2∶1)和MgSO4(2∶2)溶液中不同pH下的zeta电势.结果发现:在pH3～9之间,膜在MgCl2,MgSO4,KCl和K2SO4溶液中的等电点分别为7.4,7.0,6.9和5.5.这是由于膜表面吸附离子的迁移速率不同造成的.离子的化合价和水合离子半径对离子迁移速率的影响非常大.迁移速率更快的离子可在膜表面吸附得更多,并产生一层过量的离子层,对膜表面电荷的影响力更大.不同离子的迁移速率决定了膜不同的等电点.膜在电解质溶液中的截留结果与相应的zeta电势吻合.在等电点附近的截留为零,而往两侧逐渐升高.膜的通量在等电点处最大,往两侧逐渐降低.:聚偏氟乙烯;超滤;流动电势;等电点;渗透性能:TQ028.8　　:A　　:1007-8924(2009)05-0049-05　　[1,2]、[3,4]、[5,6],[7,8],.、[1];[9].;,,.[9-13].,[9-12][13].,zeta[11],.Pujar[13]Huisman[14]zeta,zeta.[15].,zeta,zeta..zeta,.[16];pKα[17].,,PVDF.PVDFC—F,,;,:2008-04-24:(973)(2003CB615705):(1981-),,,.＊,E-mail:[e-mail]29　5　　　　　Vol.29　No.5200910MEMBRANESCIENCEANDTECHNOLOGYOct.2009;,.PVDF,.1　理论部分1.1　zetazetaζSmolu-chowski-Helmholtz(H-S)[18]:ζ=ΔEΔPηλε(1)(1)1mmol/L[19],.PVDF,.1.2　Stern,,.,,.,f=6πηrν,η;r.,F+F-.u+/z+eu-/z-e,:ν+=F+u+z+e=fu+z+e=6πηr+ν+u+z+e,ν-=F-u-z-e=fu-z-e=6πηr-ν-u-z-e(2)u+=z+e6πηr+,u-=z-e6πηr-(3)2　实验部分2.1　(PVDF):;、KOH、KCl、MgCl2、K2SO4、MgSO4、(PEG1000,4000,10000)、(Dex-tran20000,40000)、(PVP):K30、(DMAC):;;,1μS/cm.:FukeDT-830B;Ag/AgCl、(DDS-11C)、pH(PHS-3C):.(TOC):ShimadzuTOC-VCPH,.2.2　1.,0.1MPa.,25℃.Ag/AgCl,,.,、.:5mmol/LMg2+,pH9.52,pH39,.1　Fig.1　Schematicviewofstreamingpotentialunit2.3　:1g/L(1000,4000,10000)(20000,40000),TOC,R.:1h,0.1MPa,1mmol/L4、pH,.3　实验结果和讨论3.1　2,PVDF40000(90%).、.,Huis-man[20].3.2　,[16].(3),、,、、　·50　　　·　　　　　29　2　PVDFFig.2　MWCOofPVDFmembranes.4,,.(3)rh,.rc1[21,22].,,,,1.,、.,.表1　离子的结晶半径和水合半径Table1　CrystallographicandhydratedradiusoftheionsK+Mg2+Cl-SO42-rc/nm0.1330.0990.1810.29rh/nm0.3310.4280.3320.383　1mmol/LzetapHFig.3　Zetapotentialin1mmol/Ldifferentelectrolytessolution3,MgCl2pH7.4,MgSO47.0,KCl6.9,K2SO45.4.MgCl2MgSO4KClK2SO4.(3)4:SO42-Mg2+K+Cl-.,MgSO4SO2-,MgCl2Mg2+,K2SO4K+,KClK+Cl-.1mmol/L4.,MgCl2,Mg2+,.,MgCl2zeta,Mg2+Cl-.K2SO4,zeta.pH3～7,KClzetaMgCl2.K+Cl-.MgSO4pH.,,,;,,MgSO4.3.3　4　1mmol/LpHFig.4　Rejectionin1mmol/Ldifferentelectrolytessolution4zeta,4.MgCl2,K2SO4,20%,Huisman[20].20%40000.　5:·51　　　·　,.MgSO4,,zeta,.,KClK2SO4,SO42-,,,.5,pH,4,PVDF,,;,0.8nm[11],:pH10MgSO4.,pH3～5,.4V,,.,.MgSO4,pH.5　1mmol/LpHFig.5　Fluxin1mmol/Ldifferentelectrolytessolution4　结论PVDF,.1).,,.2)zeta.,.3)pH.,.ΔE———,mVe———,CF———,C/molf=6πηrνΔP———,Par———,nmu———,m/sν———,m/sz———ε———ζ———zeta,mVη———,Pa·sλ———,S/m[1]SkartsilaK,SpanosN.Physicochemicalcharacterizationofvariouslypackedporousplugsofhydroxyapatite:treamingpotentialcoupledwithconductivitymeasurements[J].Langmuir,2006,22:1903-1910.[2]TeixeiraMR,RosaMJ,NyströmM.Theroleofmem-branechargeonnanofiltrationperformance[J].JMembrSci,2005,265:160-166.[3]UlbrichtM,SchusterO,AnsorgeW,SteigerP.Influenceofthestronglyanisotropiccross-sectionmorphologyofanovelpolyether-sulfonemicrofiltrationmembraneonfil-trationperformance[J].SepPurifTechnol,2007,57:63-73.[4]ChiuTY,JamesAE.Electrokineticcharacterisationtechniquesonasymmetricmicrofiltrationmembranes[J].ColloidSurfA,2007,301:281-288.[5]LawrenceND,PereraJM,IyerM,etal.Theuseofstreamingpotentialmeasurementstostudythefoulingandcleaningofultrafiltrationmembranes[J].SepPurifTech-nol,2006,48:106-112.[6]NakamuraK,MatsumotoK.Proteinadsorptionpropertiesonamicrofiltrationmembrane:Acomparisonbetweenstaticanddynamicadsorptionmethods[J].JMembrSci,2006,285:126-136.[7]CondomS,PersinM,LarbotA,etal.Influenceofcom-monionsduringultrafiltrationofmixturesPartI.Commonanionsmixtures[J].JMembrSci,2007,300:117-121.[8]ZengJianxian,YeHongqi,LiuHui,etal.Characteriza-tionofahollow-fiberultrafiltrationmembraneandcontrolofcleaningproceduresbyastreamingpotentialmethod　·52　　　·　　　　　29　[J].Desalination,2006,195:226-234.[9]HuismanIH,PrádanosP,HernándezA.Electrokineticcharacterizationofultrafiltrationmembranesbystreamingpotential,electroviscouseffect,andsaltretention[J].JMembrSci,2000,178:55-64.[10]NaröngP,JamesAE.SodiumchloriderejectionbyaUFceramicmembraneinrelationtoitssurfaceelectricalproperties[J].SepPurifTechnol,2006,49:122-129.[11]TsuruT,HironakaD,YoshiokaT,AsaedaM.Titaniamembranesforliquidphaseseparation:effectofsurfacechargeonflux[J].SepPurifTechnol,2001,25:307-314.[12]TanninenJ,MänttåriM,NyströmM.EffectofsaltmixtureconcentrationonfractionationwithNFmem-branes[J].JMembrSci,2006,283:57-64.[13]PujarNS,ZydneyAL.Electrostaticandelectrokineticin-teractionsduringproteintransportthroughnarrowporemem-branes[J].IndEngChemRes,1994,33:2473-2482.[14]HuismanIH,TrägårdhG,TrägårdhC,PihlajamäkiA.Determiningthezetapotentialofceramicmicrofiltrationmembranesusingtheelectroviscouseffect[J].JMembrSci,1998,147:187-194.[15]KimKJ,FaneAG,NyströmM,etal.Evaluationofelectroosmosisandstreamingpotentialformeasurementofelectricchargesofpolymericmembranes[J].JMembrSci,1996,116:149-159.[16]MartínA,MartínezF,MalfeitoJ,atel.ZetapotentialofmembranesasafunctionofpHoptimizationofisoelectricpointevaluation[J].JMembrSci,2003,213:225-230.[17]MorãoC,AlvesB,AfonsoMD.Concentrationofclavu-lanicacidbroths:InfluenceofthemembranesurfacechargedensityonNFoperation[J].J