A novel salt-swelling nanofiltration membranes for drinking water purification: High mineral ions passage and efficient organic removal

•Amino acid with aliphatic chain was selected to prepare loose polyamide membranes.•The adsorption of charged ions into the loose polyamide network causes membrane swelling.•The swollen membrane exhibits excellent separation performance for mineral ions and organics. Municipal drinking water treatment demands nanofiltration (NF) membranes with high removal efficiency for organics, high passage for mineral ions, and low operating pressure. The development of innovative and loose NF membranes is imperative. A loose-network-structured NF membrane (L-NF) was synthesized through interfacial polymerization (IP) on a PES substrate by utilizing lysine (with a flexible aliphatic chain) as standalone aqueous phase monomers. The separation performance for typical organics and mineral ions in water, as well as the permeability of the membrane were investigated. The lysine-based NF membranes exhibit a reversible and appropriate salt-induced swelling effect. The increased salt concentration leads to a significant enhancement of both permeate flux and salt passage, while maintaining unaffected removal efficiency for organics. The optimized membrane (L-NF3), synthesized with a 1 % (w/v) concentration of lysine, demonstrated remarkable retention (>98 %) for organics (humic acid and sodium alginate), while concurrently displaying low retention (5.22 %-16.40 %) for mineral ions (Mg2+ / Ca2+). Furthermore, the salts in the feed led to a substantial improvement in permeate flux (239.61 %-385.70 %) compared to salt-free feed. The Lys-TFC membrane showcased outstanding performance of separation, permeability, and operational stability, underscoring its significant potential in municipal drinking water purification. [Display omitted]