Nanofiltration membrane with ultra-narrow pore size distribution based on linear crosslinking regulation: simultaneous high-efficiency separation of mono-/multivalent anions and cations

Efficient lithium-magnesium (Li/Mg) separation is pivotal for lithium extraction from salt lake brines by nanofiltration (NF) membranes. However, high-efficiency separation requires a highly uniform pore size distribution, which poses severe challenges to the structural regulation of conventional NF membranes. Herein, a weakly negatively charged PIP-SDS/TPC membrane was constructed via interfacial polymerization (IP) between piperazine (PIP) solution containing sodium dodecyl sulfate (SDS) and terephthaloyl chloride (TPC). Molecular dynamics simulations revealed that SDS slowed down PIP diffusion and promoted its homogeneous migration into the organic phase, favoring the formation of uniform pores under the linear crosslinking by PIP with TPC. Consequently, the resulting polyamide layer exhibited a narrow pore size distribution strictly confined within the hydrated diameter of Mg 2+ , imparting ultrahigh Mg 2+ rejection and significant negative rejection of Li + , with a Li/Mg separation factor of 130. Benefiting from the synergistic effects of charge repulsion and size sieving, superior separation factor of SO 4 2− and Cl − was also achieved 304. Furthermore, the PIP-SDS/TPC membrane maintains excellent separation performance in simulated salt lake brines, with rejection rates of −15.9% to 25.7% for monovalent ions (Li + , Na + , K + ) and 97.1% to 98.7% for divalent ions (Ca 2+ , Mg 2+ ), while retaining stable performance after chemical cleaning. This work offers a new strategy for rationally designing membrane microstructures to achieve efficient Li/Mg separation.