Dual-regulated covalent organic framework membranes with near-theoretical pore sizes for angstrom-scale ion separations

Fabricating covalent organic framework (COF) membranes with molecular size cutoffs matching theoretical pore sizes is essential for selective angstrom-scale aqueous separations. We report a dual-regulation interfacial polymerization strategy to fabricate COF membranes with pore sizes approaching theoretical values, using Brønsted acid and organobase in separate phases to synchronously control polymerization and self-healing, as supported by molecular simulations of monomer diffusion and liquid chromatography-mass spectrometry analysis for component tracing. The dual-regulation COF membranes achieve a selectivity of 267 in single-salt test and an actual selectivity of 234 for K⁺/Mg²⁺ in binary systems, demonstrating a threefold increase in mono/divalent cation separation compared to single-phase-regulated membranes. Additionally, we elucidate the untrapped and trapped transport of hydrated monovalent and divalent cations within the confined cavities through molecular dynamics simulations. This work provides an alternative approach to COF membrane fabrication and advances their application in precise sieving for water purification and resource recovery.