Co-solvent microenvironment engineering promotes three-dimensional topological evolution of polyamide nanofiltration membranes to improve the permeance-selectivity balance

Conventional polyamide (PA) nanofiltration (NF) membranes are intrinsically limited by the permeance-selectivity trade-off. Herein, we developed a co-solvent microenvironment engineering strategy to regulate interfacial polymerization (IP). Introducing isopropanol (IPA) into the organic phase creates a PIP-IPA-TMC reaction microenvironment, which reduces the water/oil interfacial tension, modifies the local solvation environment, and regulates the trans -interfacial transport of piperazine (PIP). Molecular dynamics simulations indicate that hydrogen-bonding interactions between PIP and IPA retard PIP monomer diffusion. Consequently, IP shifts toward a more diffusion-regulated polycondensation regime, promoting the formation of a three-dimensional pore architecture with a highly interconnected free-volume network (accessible surface area up to 7156.40 m 2  cm −3 ) and enhanced surface negativity. Benefiting from this synergistic structural synergy, the optimized membrane achieved a water permeance of 16.3 L m −2  h −1 ·bar −1 , representing a 2.3-fold increase over the pristine PA membrane, while maintaining a high Na 2 SO 4 rejection of 98.95%. Tests using real surface water further demonstrated selective fractionation by enhancing dissolved organic matter removal while retaining a considerable fraction of essential mineral ions. This work provides a co-solvent-based interfacial regulation strategy for improving the permeance-selectivity balance of PA NF membranes for advanced water purification.