Preparation Of Novel Zwitterionic Monomer-modified Thin-layer Composite Polyamide Membranes

Thin-film composite polyamide membrane(TFC PA membrane)is an asymmetric membrane composed of a porous support layer and an ultra-thin separation layer.The TFC PA membrane has been widely used due to its good chemical stability,simple preparation process and high separation efficiency,especially in Nanofiltration(NF)and reverse osmosis(RO)technologies are widely used.However,the low permeability and serious fouling of TFC PA membrane in the separation process are two hurdles that restrict the further promotion and application of TFC PA membrane.In recent years,due to its good chemical stability,in order to prepare high-performance anti-fouling TFC PA membranes,in this work,the synthesized zwitterionic monomers and natural zwitterionic monomers were introduced into the TFC PA membrane structure by incorporation of zwitterionic monomers and layer-by-layer interfacial polymerization(LBL-IP)technology,and the TFC PA membrane with a rich zwitterionic structure inside and on the surface is prepared.Modification of zwitterionic monomers improves the membrane permeability and anti-fouling performance.The major contents and results of this research are as follows:(1)Preparation and performance study of TFC NF membrane with aromatic diamine zwitterionic monomers as aqueous comonomersIn this experiment,an aromatic diamine zwitterionic monomer 3-(4-(2-((4-aminophenyl)amino)ethyl)morpholino-4-onium)propane-1-sulfonate(PPD-MEPS)was designed,synthesized through three steps reaction.As a p-phenylenediamine(PPD)derivative,PPD-MEPS possesses two active amine units,which can react with trimesoyl chloride(TMC)in the organic phase during the interfacial polymerization(IP)reaction process.Thus,the superhydrophilic zwitterions were not only on the membrane surface but also across the whole PA layer to facilitate water molecule transportation.With increasing loading content of PPD-MEPS in PIP aqueous solution,the as-fabricated nanofiltration membranes(NFMs)exhibited higher hydrophilicity,increased active layer thickness,and molecular weight cut off.In addition,the fouling experiments illustrated that the fouling resistance of the zwitterion-modified NFMs to bovine serum albumin(BSA)was significantly improved.After 12 h of solution filtration test,the FDR of the pristine membrane was 44.5%,whereas it just reduced27.4% for the zwitterion-incorporated membrane NFM-4.In addition,the flux recover ratios(FRR)after rising were 71.5 and 85.4%.(2)Preparation and performance of TFC RO membrane with zwitterionic small molecules grafted onto the surfaceIn order to further increase the content of zwitterionic monomers on the surface of PA membranes,small-molecule zwitterions were used to functionalize polyamide membrane surface through layer-by-layer interfacial polymerization(LBL-IP)to improve the performance of RO membranes.Zwitterionic molecules 3-(4-(2-((4-aminophenyl)amino)ethyl)morpholino-4-ium)propane-1-sulfonate(PPD-MEPS)and amino acid arginine were covalently bonded onto the PA surface via the amine groups of two zwitterions.Consequently,the surface hydrophilicity of both modified membranes were significantly improved with WCA decreased from ?60° to ?28°,and their surface negative charge also decreased to some extent at high p H values.The water permeability increased from 2.45 LMH/bar to 3.85 LMH/bar,increasing by about 57%,while maintained a Na Cl rejection as high as 98.5%.In addition,the zwitterionsmodified RO membranes exhibited much improved antibacterial attachment(E.coil)and fouling resistance to model foulants bovine serum albumin(BSA),lysozyme(LYZ)and humic acid(HA).Membranes modified with natural Arg and PPD-MEPS showed similar anti-fouling performance.