Surface modification of NF membrane with zwitterionic polymer to improve anti-biofouling property

The zwitterionic poly-(carboxybetaine methacrylate) (PCBMA) was grafted on two commercial nanofiltration (NF) membranes surfaces to improve the easy-cleaning, anti-adhesive and anti-microbial properties of the membranes. Based on the amine and carboxylic acids groups of NF membranes, the commercial NF membranes (NF90 and NF270) were modified by the redox initiated graft polymerization to obtain the NF90-PCBMA and NF270-PCBMA membranes. The membranes before and after modification were characterized by ATR-FTIR and XPS to analyze the change of the membrane surface chemical structure characterization, and also by contact angle analyzer, zeta potential analyzer, SEM and AFM to analyze the change of the membrane surface physical characterization. The zeta analysis (at pH 7.0) indicated that the NF90-PCBMA and NF270-PCBMA membranes surfaces were near electrically neutral, while the unmodified NF membranes surfaces were negatively charged. The NaCl and MgSO4 solutions were used to analyze the permselectivity of the membranes, which changed little after modification. The aqueous solutions containing positively charged lysozyme and negatively charged bovine serum albumin were used to analyze the anti-adhesive property of the membranes, and the water fluxes of the modified membranes were all decreased less than those of the unmodified membranes. After the membranes being cleaned, the water flux recovery rates of the modified membranes were all above 90% and much higher than those of the unmodified membranes. The anti-microbial property of the membranes was analyzed by being contacted with Escherichia coli and bacillus subtilis, the mortality of which could reach to 99%. The PCBMA modification method had improved the anti-adhesive, anti-microbial and easy-cleaning properties of two aromatic polyamide NF membranes without sacrificing the permselectivity of the membranes. What's more, this method may be suitable for all aromatic polyamide membranes to increase the anti-biofouling property.