Decoupling interface regulation and L-arginine interface empowerment to construct stable Mg2+/Li+ separation positively charged polyamide nanofiltration membranes

RIP microenvironment regulation and amino acid functionalization synergize NF design. • BDM scavenges H + to suppress PEI protonation and preserve reactivity. • L-Arginine functionalization enhances membrane hydration and positive charge. • P-B-0.8/A-0.1 membrane achieves 99.5% Mg 2+ rejection and an SF of 131.7. • After 80 h, MgCl 2 rejection >98%, showing stable and antifouling performance. Thin-film composite (TFC) nanofiltration (NF) membranes show great potential for Mg 2+ /Li + separation. However, during conventional interfacial polymerization, excessively rapid amine diffusion and local acidification at the reaction interface can lead to nonuniform interfacial reactions. This study proposes a synergistic construction strategy of membrane forming microenvironment regulation and amino acid interface empowerment. Bis (2-dimethylaminoethyl) ether moderated the apparent migration and protonation behavior of polyethylenimine and alleviated local acidification at the reaction front. Subsequent L-arginine post modification enhanced surface hydration and modified the acid–base/charge characteristics of the polyamide layer interface. P-B-0.8/A-0.1 membrane with high positive surface charge (IEP pH = 8.5), excellent antifouling properties, and a uniform pore-size distribution were constructed for Mg 2+ /Li + separation. In the MgCl 2 /LiCl mixed salt system, the membrane achieved an Mg 2+ rejection rate of 99.5% and a separation factor of 131.7. During 80 h of continuous operation, the Mg 2+ rejection rate remained above 98%. Moreover, the P-B-0.8/A-0.1 membrane exhibited excellent flux recovery and anti-scaling stability during BSA and lysozyme fouling cycles, as well as in CaSO 4 and CaCO 3 inorganic scaling systems.