Multi-carboxyl based zwitterionic nanofiltration membrane with ion selectivity and anti-scaling performance

Abstract

Membrane scaling is one of the drawbacks of nanofiltration (NF) impeding its wide application in treatment of salt-containing water. Especially, the high concentration of Ca2+ and SO42− easily lead to a CaSO4 scale layer on the membrane surface, limiting the separation process. Herein, a zwitterionic NF membrane with anti-scaling performance was fabricated through multi-carboxyl carboxylate (sodium citrate) incorporated by interfacial polymerization. Due to the synergistic effect of sodium citrate, the resulting NF membrane had a more negatively charged surface and a larger pore size than the pristine membrane. In desalination, this zwitterionic NF membrane exhibited a high selectivity (15.9) between SO42− (73.1 ± 2.4% rejection) and Ca2+ (4.6 ± 1.4% rejection) with a flux of 39.6 LMH, much higher than that of the commercial NF membrane (NF-270, a selectivity of 1.5). Based on the high SO42− and Ca2+ selectivity, it is difficult to form a CaSO4 scale layer on the membrane surface, which yields an excellent anti-scaling performance of the resulting membrane. Furthermore, the zwitterionic monomer endowed the membrane with an anti-fouling effect due to zwitterions materials have strong hydration to resist nonspecific protein adsorption. This design strategy of ion selectivity zwitterionic membranes through the incorporation of carboxylate provides guidance for the design of highly ion selective anti-scaling NF membranes, which has potential applications in water treatment for salt-containing solutions.