Preparation And Properties Of Polyethyleneimine Charged Nanofiltration Membrane

Nanofiltration membranes are in great demand in the field of water pollution control due to their high permeation flux and high retention capacity for divalent ions.So far,most commercial nanofiltration membranes are electrically neutral or negatively charged.Although research on positively charged nanofiltration membranes has gradually increased in recent years,but it has the problems of low permeation flux and poor anti-pollution performance,so there has lots potential to develop.In order to improve the permeability and anti-pollution performance of the nanofiltration membrane,using polyethyleneimine（PEI）as the water phase and trimethyl chloride（TMC）as the organic phase,a highly positively charged PEI/TMC/PEI composite nanofiltration membrane was prepared by interfacial polymerization on a polyethersulfone（PES）ultrafiltration membrane.Through the reaction of cyanuric chloride（CC）with the amine groups on the membrane surface,the PEI/TMC/PEI/CC composite nanofiltration membrane was prepared by the method of secondary interfacial polymerization.Through the ring-opening reaction of 1,4-butane sultone（1,4-BS）and tertiary amine on the surface of the membrane,the PEI/TMC/PEI/1,4-BS composite nanofiltration membrane was prepared.This study optimized the conditions in process such as the concentration and the immersion time of reactants,and used FTIR、XPS、SEM、AFM、WCA、Zeta potential to characterize the physicochemical properties and microstructure of the membranes.In addition,this experiment used the cross-flow filtration method to explore the separation performance of membranes on inorganic salts and dyes.The influence of operating conditions on the performance and anti-fouling performance of the membranes were discussed.The optimized conditions are as follows:the deposited PEI mass fraction is 0.05%;the TMC mass fraction is 0.05%;the immersion time of TMC solution is 3min;the surface PEI concentration is 2 g/L;the CC concentration is 0.1 g/L;the immersion time of 1,4-BS solution is 10h.After introducing CC on the PEI/TMC/PEI membrane,the secondary interfacial polymerization increases the thickness of the selective layer,and the roughness of the membrane decrease to a certain extent,the consumption of amine groups reduces the hydrophilicity.After the introduction of 1,4-BS on the surface of the PEI/TMC/PEI membrane,the reaction of sultones with tertiary amines forms zwitterionic units,which increases the hydrophilicity of the membrane.The pure water permeability coefficient of the PEI/TMC/PEI composite membrane is 57.58 L·m^-2·h^-1·MPa^-1,after introducing CC,the pure water permeability coefficient of the membrane decreased by 35.71%,and the pure water permeability coefficient of the PEI/TMC/PEI/1,4-BS composite membrane is significantly improved to 79.62 L·m^-2·h^-1·MPa^-1.The composite membranes showed good rejection for divalent cationic salts and positively charged organic dye molecules,the rejection of Mg Cl₂ and DB56 can reach 90%and 95%,respectively.In the anti-fouling experiment,the PEI/TMC/PEI/1,4-BS membrane has excellent anti-fouling performance,the flux recovery rate of BSA,LYZ and HA can reach 90%.