Surfactant Interlayer-Tuned Positively Charged Nanofiltration Membranes via Kinetics-Enhanced Interfacial Polymerization for Ultrahigh Li⁺/Mg²⁺Selectivity in Salt-Lake Brines

The burgeoning energy sector exhibits a demand for lithium resources. Notably, salt lakes, rich in lithium, challenge due to the high Mg²⁺/Li⁺ ratios encountered. Nanofiltration, characterized by its simplicity, environmental sustainability, holds promising prospects for Mg²⁺/Li⁺ separation in salt lakes. Density functional theory (DFT) simulations reveal that sodium dodecyl sulfate (SDS) surfactant layers significantly lower the energy barrier for polyethylenimine (PEI) transfer, which fundamentally enhances the interfacial polymerization kinetics. This study activates polysulfone (PSF) ultrafiltration (UF) membrane surfaces with SDS surfactants to form a negatively charged surface-active interlayers, the hydrophilicity of the membrane surface was increased and then accelerating polymerization at the PEI/TMC interface. Under optimized conditions, the membranes achieve 98.6% MgCl₂ retention and ultrahigh selectivity (<i>S</i>_(Li/Mg) = 118.75) with a Mg²⁺/Li⁺ ratio of 50:1, showing sustained performance in a 44 h test. This work provides efficient separation method for high-performance lithium extraction from salt lake brines.