Engineering Polyamide Networks via Synergistic Surfactant Regulation and Solvent Treatment for Efficient Ion Separation

Separating monovalent ions from divalent ions remains a central challenge in resource recovery. While the classic poly(piperazine-amide) nanofiltration membrane exhibits superior rejection of divalent anion, the application in cation separation is constrained by the strongly negatively charged surface and limited size-sieving precision. To address this limitation, we propose a solvent treatment-induced optimization strategy for surfactant-tailored polyamide networks. The surfactant-assisted interfacial polymerization yields a dense and uniform nascent polyamide network that can withstand solvent treatment while preserving its cross-linked structure. Subsequent solvent treatment selectively removes oligomers trapped within the network, thereby refining the polyamide network architecture. This strategy facilitates the formation of a thinner polyamide selective layer that exhibits an attenuated negative surface charge and a more uniform pore size distribution. The optimized membrane achieves a dual enhancement in performance, exhibiting high mono-/divalent ion selectivity (Li + /Mg 2+ selectivity of 96.1 and Cl – /SO 4 2– selectivity of 1351) coupled with a high water permeance of 14.9 L m –2 h –1 bar –1 . This work provides a straightforward and effective method to refine surface properties and internal architecture of polyamide networks for efficient mono-/divalent ion separation.