A New Strategy for Tunable Pore Size Polyamide Nanofiltration Membranes during the Interfacial Polymerization by the Dynamic Hydrophilic Site Resistance Balance of 3-Aminobenzenesulfonamide in the Aqueous Phase

The growing demand for lithium-based materials stems predominantly from the rapid proliferation of renewable energy technologies. Given the growing demand for lithium, extracting the metal from salt lake brines has gained significant research attention. While positively charged nanofiltration (NF) membranes exhibit promising Mg²⁺/Li⁺ separation efficacy, the interfacial polymerization technique remains constrained by the inherent permeability-selectivity trade-off. This study optimized the microstructure and surface properties of the polyamide (PA) separation layer by regulating the additional amount of 3-aminobenzenesulfonamide (ABSA) based on the principle of hydrophilic steric dynamic equilibrium. The best-performing membrane, with 0.05 ABSA added, was the polyethylenimine (PEI)/trimesoyl chloride (TMC) NF membrane sample (PEI/ABSA-0.05-TMC), which retained 93.7% of Mg²⁺ and 28.4% of Li⁺. Compared to the PEI-TMC NF membrane without ABSA addition, water flux was increased from 12.5 L·m^–2·h^–1·bar^–1 to 17.7 L·m^–2·h^–1·bar^–1, MWCO was adjusted from 584 to 487 Da, and the corresponding separating factor of S_Li,Mg increased from 8.51 to 13.3. Throughout prolonged experimental trials, the PEI/ABSA-0.05-TMC NF membrane demonstrated sustained separation stability. This work establishes a robust framework for optimizing NF membranes, providing a strategic pathway toward Mg²⁺/Li⁺ separation technologies.