Tailoring subnanometer transport pathways in polyamide nanofiltration membranes for high-permeance Li+/Mg2+ separation

A SISAIP strategy was developed to regulate interfacial PA formation. • SDS/NaCl regulation produced ultrathin PA layers with sub-nanometer pathways. • The membrane achieved S Li, Mg of 90.9 and permeance of 9.5 L m −2  h −1  bar −1 . • Stable operation and strong flux recovery were obtained under brine-relevant tests. The rapidly increasing global demand for lithium has stimulated the development of advanced membrane technologies for lithium extraction from salt-lake brines. Nanofiltration (NF) membranes with precisely regulated subnanometer transport pathways are highly attractive for Li + /Mg 2+ separation; however, the rational construction of selective layers that simultaneously deliver high ion selectivity and fast water transport remains challenging. Herein, we report a scalable surfactant–inorganic salt–assisted interfacial polymerization (IP) strategy, termed SISAIP, to fabricate high-performance polyamide NF membranes. Interfacial tension, dynamic light scattering, and UV–vis analyses indicated that sodium dodecyl sulfate enriched at the water/oil interface and regulated PEI transport across the interface, whereas NaCl modified the aqueous-phase microenvironment, moderated PEI diffusion toward the interface, and helped confine the interfacial reaction zone. This coordinated regulation produced an ultrathin PA selective layer with an apparent thickness of 11.2 ± 0.6 nm and compact subnanometer transport pathways. The optimized membrane achieved a water permeance of 9.5 L·m −2 ·h −1 ·bar −1 , an S Li,Mg of 90.9, and Mg 2+ rejection above 99.5%, corresponding to 578.6% and 437.9% increases in water permeance and S Li,Mg over the control T-IP membrane, respectively. The membrane also maintained stable performance during 120 h of continuous filtration and exhibited favorable fouling/scaling resistance, with a flux recovery ratio of 100% under organic-conditioned CaSO 4 scaling conditions. This SISAIP strategy provides a promising and scalable route for designing advanced NF membranes toward efficient lithium recovery from salt-lake brines.