Preparation of anti-fouling zwitterionic nanofiltration membrane with tunable surface charge

Anti-fouling property is of vital significance and remains a challenge in the membrane separation field. In this work, N-diethylethylenediamine (DEEDA) was incorporated into the polyamide matrix first. Then, an anti-fouling zwitterionic nanofiltration membrane with tunable surface charge was fabricated by the grafting of p-xylylene dichloride (XDC) on the membrane surface. The resulting nanofiltration membrane possessed zwitterionic groups of positively charged N⁺ and negatively charged COO^-. Meanwhile, the surface charge could be tuned precisely by the concentration of XDC. A neutrally charged nanofiltration membrane was obtained when the concentration of XDC was 1.0 ​wt% and the preparing membrane showed permeance of 9.1 ​L·m^-2·h^-1·bar^-1 with high rejection of CaCl₂ (90.8%) and Na₂SO₄ (91.3%) at pH ​= ​6.5. This membrane exhibited excellent anti-fouling properties towards not only negatively charged bovine serum albumin but also positively charged lysozyme. The optimum membrane, PA-XDC-1.0, had flux recovery rates of 95.0% and 94.0% for bovine serum albumin and lysozyme, respectively, which was higher than those of PA-DEEDA-0 (86.1% and 80.7%). This work offered a facile way to fabricate an anti-fouling zwitterionic nanofiltration membrane with tunable surface charge, which had wide applications in water purification.