Dual-Regulation of Interfacial Polymerization via Interlayer and Surfactant: Molecular Dynamics Insights and High-Performance Mg2+/Li+ Separation Nanofiltration Membrane

Abstract

Abstract A polyamide nanofiltration (NF) membrane with high permeance and Mg2+/Li+ selectivity was developed through a dual regulation strategy combining a tannic acid (TA) and Al3+ coordination interlayer with sodium dodecyl sulfate (SDS). Molecular dynamics simulations showed that surfactant structure significantly affects the interaction and molecular mobility of polyethylenimine (PEI), with SDS providing effective regulation of PEI transport behavior. The TA and Al3+ coordination interlayer regulates PEI retention and local supply near the substrate surface, while SDS modulates PEI molecular mobility, providing complementary regulation of interfacial polymerization. Structural characterization showed that the dual regulation strategy promoted the formation of a thin and hydrophilic polyamide selective layer and decreased the proportion of surface carboxyl groups from 23.51% for the pristine PA membrane to 13.36% for the TA-Al3+/PA-SDS membrane, resulting in favorable surface charge characteristics. The optimized membrane exhibited a MgCl2 rejection of 99.26%, a LiCl rejection of 32.9%, an Mg2+/Li+ separation factor of 44.36, and a water permeance of 10.21 L·m−2·h−1·bar−1. The membrane also maintained relatively stable separation performance during 72 h filtration. These results demonstrate that coordinated regulation of PEI supply and molecular mobility provides an effective strategy for constructing high performance NF membranes for Mg2+/Li+ separation and lithium recovery from brines.