Improving the water flux and bio-fouling resistance of reverse osmosis (RO) membrane through surface modification by zwitterionic polymer

Biofouling is a critical problem to the development of reverse osmosis (RO) membrane technology. In this study, a commercial available aromatic polyamide RO membrane (TE membrane) was surface modified to improve its permselectivity and anti-biofouling property. The TE membrane was modified by the redox initiated graft polymerization of N,N′-dimethylaminoethyl methacrylater (DMAEMA), followed by the surface quaternization reaction with 3-bromopropionic acid (3-BPA) to obtain the zwitterionic carboxybetaine methacrylate (CBMA) polymer chains on the membrane surface and the modified membrane was named TE-PCBMA membrane. The grafting of DMAEMA and the quaternization reaction were analyzed by ATR-FTIR and XPS. The zeta analysis (at pH 7.0) indicated that the TE-PCBMA membrane surface was near neutrality, while the unmodified TE membrane surface was negative charged. The water flux of the TE-PCBMA membrane increased 22.55% than that of the unmodified membrane, while the salt rejections of the membranes were nearly the same. The proteins fouling tests (contaminations were positively charged lysozyme and negatively charged bovine serum albumin, pH 6.8), indicated that the water fluxes of the TE-PCBMA membrane all decreased less than those of the unmodified TE membrane, and after the membranes were cleaned, the water flux recovery rates of the TE-PCBMA membrane were higher than 92%, which were far higher than those of the unmodified TE membrane. Moreover, the mortality of Escherichia coli and Bacillus subtilis, after contacted with the TE-PCBMA membrane, could reach to 99%. The results indicated that the TE-PCBMA membrane had improved water flux, and was endowed easy-cleaning, anti-adhesive and anti-microbial properties to prevent bacterial deposition and growth on the membrane surface.