Zwitterionic in situ modification of polyamide NF membranes for antifouling performance

Membrane fouling and the permeability-selectivity trade-off remain central challenges in nanofiltration (NF) technology. Here, we report a one-step, aqueous-phase in situ surface modification strategy for polyamide (PA) NF membranes, in which the novel polyhydroxy zwitterionic compound 2-[bis(2-hydroxyethyl) (phenyl) amino] ethane-1-sulfonate (Z-PDEOA) is covalently grafted onto residual acyl chloride groups of the PA layer via esterification. Successful Z-PDEOA immobilization imparted the resulting PA-Z-PDEOA NF membrane with markedly improved surface hydrophilicity (water contact angle reduced to 6.7°) and a smoother, more homogeneous polyamide-polyester separation layer. The optimized PA-Z-PDEOA NF membrane had a water flux 3.4 times that of the original PA NF membrane. Meanwhile, the MgSO₄ rejection rate increased to 97.58%, and the flux recovery rates for bovine serum albumin (BSA) and humic acid (HA) reached 99.81% and 93.25%, respectively. In the three dynamic BSA contamination tests, it was further demonstrated that the PA-Z-PDEOA NF membrane has excellent antifouling performance. These results establish Z-PDEOA grafting as an effective and scalable approach to designing high-performance antifouling NF membranes that simultaneously overcome the permeability-selectivity trade-off.