Macrocycle-based covalent organic networks for ultrafast sub-1-Å precision ion sieving

The water-energy nexus demands membranes with subångström ion-sieving precision, a capability hindered by the intrinsic selectivity limits of conventional materials. We fabricated ultrathin covalent organic network (CON) membranes via interfacial polymerization of 1,4,7,10-tetraazacyclododecane (cyclen) with either terephthaloyl chloride or isophthaloyl chloride. The resulting architectures demonstrate narrow pore size distribution and subångström-level ion resolution. CON-T membranes exhibit exceptional water permeance (22.2 liters per square meter per hour per bar) along with Li⁺/Mg²⁺ and Cl^-/SO₄^2- selectivities of 82.6 and 118.1, respectively. Monomer conformation engineering yielded CON-I membranes that set high benchmarks for Li⁺/Mg²⁺ (326.7) and Cl^-/SO₄^2- (376.9) selectivity. At the process scale, CON-T membranes facilitate highly efficient lithium resource extraction (97.4% recovery with 99.3% purity), while CON-I membranes enable Cl^- production at ~99.9% purity from industrial wastewater. This methodology establishes a paradigm for high-resolution ion-sieving membranes that is fully compatible with industrial-scale polymeric membrane manufacturing, offering a viable solution for next-generation water-energy systems.