Constructing a zwitterionic ultrafiltration membrane surface via multisite anchorage for superior long-term antifouling properties

Zwitterions bearing balanced charge groups have attracted increasing attention to fabricate antifouling membranes due to their highly hydrated structure. The simple and efficient method of covalent connection to enhance the stability of the zwitterions on membrane surfaces is still challenging. Herein, s branched polyethyleneimine (PEI) was employed to synthesize the zwitterion by a quaternary amination reaction with sodium chloroacetate. A novel zwitterionic surface with neutral surface charge was constructed by grafting the PEI-based zwitterion (Z-PEI) onto the hydrolyzed PAN (H-PAN) membrane surface. Covalent bonds were formed between the Z-PEI and H-PAN membrane while the electrostatic attraction would promote this reaction. The zwitterionic membranes exhibited superior antifouling ability (flux recovery ratio of about 99.8% and total flux decline of about 31.4%) due to the formation of a tight hydration layer by zwitterions on the membrane surface. Furthermore, the flux recovery ratio was not changed obviously during the long term experiment and could be maintained at as high as 96.3 and 98.4% after immersion in acid and alkali solution, respectively. These results demonstrated that the long term and chemical stability of zwitterionic functional surfaces were significantly enhanced via multisite covalent anchorage.