Molecular manipulation of polyamide nanostructures reconciles the permeance-selectivity threshold for precise ion separation.

Membrane nanofiltration (NF) has emerged as a prominent technology for efficient separations of ions, but state-of-the-art polyamide (PA) NF membranes are constrained by a pernicious tradeoff between water permeance and selectivity. This work conceives a versatile molecular engineering strategy to simultaneously improve water permeance and co-cation selectivity through molecular construction of cationic triazolyl heterocyclic polyamide (CTHP) nanofilms via scalable interfacial polymerization. Experimental data and molecular simulations reveal that the CTHP structures precisely regulate the subnanometer pore architecture and binding affinity with water and ions, affording advanced size-sieving and Donnan exclusion while facilitating water partitioning and transport. The exemplified PA membrane exhibits ultrahigh divalent cation rejections of over 99% with a 9-fold increase in monovalent/divalent cation sieving selectivity relative to the pristine benchmark, exceptional water permeance, and good fouling resistance. The implemented molecular engineering strategy holds broad prospects for the rational design of high-performance polymeric membranes for sustainable and precision separations.