Swelling-thermal crosslinking engineered polyamide nanofiltration membranes for high-performance Mg2+/Li+ separation

Lithium extraction from hypersaline brines is increasingly important for sustainable energy technologies. Nanofiltration membranes leverage synergistic size exclusion and Donnan effects for Mg 2+ /Li⁺ separation under high-salinity conditions. However, a persistent flux-selectivity dilemma remains, because the highly crosslinked and compact polyamide selective layers required for high Mg 2+ rejection often introduce substantial mass-transfer resistance and limit water flux. Here, we develop a methanol swelling followed by thermal curing strategy to regulate the polyamide network architecture. Swelling promotes structural relaxation and pathway opening, whereas post-curing stabilizes the reconfigured network and narrows the pore-size distribution to strengthen size-sieving. The resulting membrane (PEI-TMC-M h ) delivers a permeation flux of 56.65 L·m −2 ·h −1 in 2000 ppm MgCl 2 while maintaining Mg 2+ rejection above 98%. In simulated brine with Mg 2+ /Li + = 50, a separation factor (S Li/Mg ) of 34.03 is achieved. Two-stage nanofiltration of real salt-lake brine (Mg 2+ /Li + mass ratio 55) yields a Li + -enriched solution containing 26.9 mg·L −1 Li + with a reduced Mg 2+ /Li + mass ratio of 0.65. This work provides a simple post-treatment route to improve the flux–selectivity balance for brine-based lithium extraction.