Engineering a novel zwitterionic polyurethane nanofiltration membrane with enhanced fouling resistance for water reclamation

Design of zwitterionic polymers with feasible methods is rational for grafting membrane surface and enhancing its antifouling property. Herein, we propose a facile and scalable “one-pot” polymerization approach to synthesize a novel thiolated zwitterionic polyurethane (TZP) and graft it onto a polydopamine activated membrane surface via Michael addition for engineering antifouling nanofiltration (NF) membranes. The chemical structure of TZP was confirmed by the 1H nuclear magnetic resonance and it had a weight average molecular weight of 13,000 g mol−1. The Fourier transform infrared and X-ray photoelectron spectra confirm the successful introduction of sulfobetaine groups on membrane surfaces. The TZP grafting neutralized the negative charge of PDA interlayer and further improved membrane hydrophilicity. The pore size and ion selectivity of the NF membranes were optimized by tuning TZP concentrations. Satisfactory divalent anion retention along with a molecular weight cut-off of ∼800 Da was achieved at 30 g L−1 TZP concentration (i.e., TZP-30). During two cycles of synthetic wastewater filtration, the TZP-30 membrane exhibited excellent fouling resistance and satisfactory flux recovery rate compared with a benchmark commercial NF membrane. Our findings shed light on the future design of novel zwitterionic polymers and antifouling NF membranes for sustainable water reclamation.