Reversible Bond Dynamics Enable Crystallinity-Healed COF Membranes for Selective Ion Transport.

Covalent organic frameworks (COFs) offer ordered, nanometer-scale channels with programmable chemistry and topology, making them promising membrane materials for selective ion transport. However, fabricating robust COF membranes that preserve high crystallinity remains a key challenge. Here we directly address this challenge by decoupling crystallization from membrane formation. COF membranes are first made by interfacial polymerization and subsequently healed under acid-catalyzed hydrothermal conditions, which activate reversible COF linkage bond exchange and framework self-correction. Using TpPa-SO3H as a model, this healing process enhances the (100) x-ray diffraction peak intensity by 25-fold, resulting in a 375% increase in proton conductivity and enhanced monovalent cation-cation selectivity. This "make-then-heal" strategy leverages dynamic covalent chemistry to produce structurally precise, crystallinity-healed COF membranes.