Polyamide nanofiltration membrane fabricated via a metal-chelate strategy for high-flux desalination

Nanofiltration (NF) technology, utilizing polyamide (PA) membranes fabricated through interfacial polymerization (IP), has found extensive application in desalination processes. The pursuit of enhancing water permeance while maintaining high rejection rates of NF membranes has garnered substantial research attention. This study proposed a metal-chelate strategy by incorporating calcium chloride (CaCl2) as an aqueous additive during the IP process and employing EDTA-4Na for post-treatment. In the presence of Ca2+, the EDTA-4Na-soaked membrane achieved suitable swelling to better regulate membrane pores, which benefited water flux enhancement and avoided severe structural defects. Meanwhile, the modified membrane also showed a more hydrophilic and negatively charged surface, leading to a significant performance in removing Na2SO4. As a result, the optimized membrane exhibited a water flux of 24.6 L m−2 h−1 bar−1, nearly 3 folds that of the initial PA membrane, while maintaining a satisfactory Na2SO4 rejection (97.2 %). Moreover, the obtained membrane showed good operation stability and anti-fouling properties during long-term use. This work proves that the metal-chelate strategy can be an efficient modification method and inspires the fabrication of high-performance NF membranes with coupling processing.