Impacts of weak acid or alkali post-treatment on properties and performance of thin-film composite nanofiltration membranes

Nanofiltration, an efficient process for separation of ions and organic matters, is paid universal attention to meet various requirements of water treatment. To tailor membrane performance, solution post-treatment has been demonstrated as one of effective approaches, while the efficacies and underlying mechanisms of the easily accessible reagents, i.e., weak acid or alkali solutions, remain to be explored. Herein, a systematical investigation was launched on the membrane post-treatment using several kinds of weak acid/alkali solutions with simultaneous heating. It was revealed that the solution pH mainly affected the proton migration during post-treatment and thus the further cross-linking tendency of the nascent membrane. Moreover, the specific acid/alkali species could also exert different impacts on physicochemical properties especially zeta potential of the resultant membranes. All the treated membranes had molecular weight cut-offs in the range of 200 to 250   Da with a water permeance of 20~30   L   m -2 h -1 bar -1 , competitive in achieving efficient separation. Among them, the NaHCO 3 -treated membrane had the densest pore structure, while the Na 2 CO 3 -treated one was the most permeable. This research provided some insights on acid/alkali solution post-treatment and could be referenced to guide mild and facile membrane customization targeting different performance.