A novel loose nanofiltration membrane with superior anti-biofouling performance prepared from zwitterion-grafted chitosan

Developing a novel loose NF membrane with zero NaCl rejection as well as effective anti-adhesive and anti-bacterial properties is significant for recycling and purification applications in many industries. A novel anti-biofouling loose nanofiltration (NF) membrane was fabricated by crosslinking a graft copolymer chitosan-g-poly(sulfobetaine methacrylate) (CS-g-PSBMA) as selective layer of a thin film composite (TFC) membrane for dye/salt separation. Specifically, CS-g-PSBMA was synthesized using cerium (IV) ion as the oxidant to initiate the graft polymerization of SBMA from CS. The PSF membrane was pre-wetted with hyperbranched polyethylenimine solution, then the loose NF membrane was fabricated by crosslinking CS-g-PSBMA with glutaraldehyde on the polysulfone (PSf) ultrafiltration membrane as the support layer. Upon optimization, the membranes show minimal rejection rates to NaCl or MgCl2, which is less than 5% but high rejection to dye molecules. After maintaining the pressure for 6 h, the interception rate for Congo red/mixed salts remained at 98% and that for methyl green/mixed salts was 80%. Further, experiment results show that the stable anti-bacterial rates of loose NF membrane against Escherichia coli and Staphylococcus aureus reached 98.3% and 99.0%, respectively.