Investigation On Preparation And Performance Of Self-assembly Nanofiltration

Preparation of multilayer polyeletrolyte films (MPFs) involves alternatingimmersion of a charged substrate into solutions containing oppositely chargedpolyelectrolytes. In this procedure, the thickness of the polyelectrolyte membrane canbe easily controlled on nanometer scale, and the thickness, charge density, andcomposition of the active skin layer can be flexibly changed. Excellent performanceof NF membranes can be prepared by LBL, In process of preparation, the methods ofdynamic has advantages in fewer number NF membranes, So,it can be concerned.In this work, two kinds of polyelectrolytes, PSS and PDADMAC, were selectedto investigate on the preparation of polyelectrolytes multilayer nanofiltrationmembranes on polysulphone (PS) ultrafiltration membrane by three kinds oflayer-by-layer self-assembly methods such as static, dynamic and dynamic-staticpreparation process separately. The prepared LBL membranes were characterized bySEM, AFM, ATR-FTIR, streaming potential, and contact angles analysis, as well asthe separation performance analysis using NaB2BSOB4B (2,000mg/L) and NaCl(2,000mg/L), respectively, at 1.0MPa. The mechanism of layer-by-layer self-assemleywas analyzed.In static preparation process, the influence of different substrate on theperformance of the prepared nanofiltration membrane was firstly investigated to selectthe most suitable substrate membranes for the MPFs. The effects of concentration andtype of the support electrolytes on the membrane performance were also investigatedand the results showed that NaCl is the suitable support electrolyte and its optimalconcentration is 0.5mol/L.The SEM and AFM of the static MPFs: indicated that theprepared NF membrane surface was relatively uniform and with no defect,and theroughness was adout 10.15nm.The 1033cm^-1 absorption peak of the sulphonic base on the ATR-FTIR spectrum of (PDADMAC/PSS)BnB membranes increases gradually with the increase of the bilayer number,which is a demonstration of the LBL assemblyprocess The alternately variations of both Zeta potential and contact angle with thelayer number also reflect the alternate assembly process For the best case,the(PDADMAC/PSS)5 NF membranes prepared by static process showed excellentperformance,the rejection of Na₂S0₄ was 93%mad membrane flux was 60 L/m²h,and the rejection of NaCl was only 13%,while the flux could reach 80 L/m²h,which indicates that the prepared LBL NF membranes have excellent ionic selectivity．In dynamic preparation process,preparation pressure and type and concentrationof different supporting electrolytes were firstly investigated Excellent performancecould be obtained with both kinds of supporting electrolytes,MgCl₂,at concentrationof 0 5mol/L under preparation pressure of O 2MPa Investigation also shown thatPDADMAC as the first deposition layer is relatively adva^tagous for preparationMembrane flux was measured by electronic balance,which indicated that thedeposition of the first deposited of two bilayers of is crucial Both SEM and AFMindicated that the prepared NF membrane surface was uniform and with no defectContact Angle is different between PSS/PDADMAC mad PDADMAC/PSS For thebest case,the prepared(PDADMAC/PSS)₄ NF membrane showed a 90%rejection ofSO₄^2-mad a solutionflux of50⁶0L/m²hat 1 0MPaTo combining the advantages of static and dynamic preparation methods,vc-eproposed a dynamic static method to prepare the self-assembly nanofiltrationmembrane Fator of assembling time were inspected during the whole preparationprocess SEM,AFM and contact angle reflect the feasibility of dynamic-static processIn this case,the prepared(PDADMAC/PSS)₃ NF membrane showed a 90%rejectionofSOd。。mad a solution flux of 50～60L/m²h at 1 0 MPa Result showed that dynamic-static method is relatively advantagous for fewerlayer MPFs The analysis of filtration resistance indicated that the deposition of thesecond bilayer is crucial in the whole preparation process The speed of deposition indynamic-static is more quickly than static and dynamic assembling...