Molecular welded interface engineering to synthesize covalent organic framework membranes for ultrafast molecular sieving

Covalent organic framework (COF)-based membranes exhibit exceptional potential for molecular separation owing to their well-defined nanoporosity, tailorable pore apertures, and high surface-to-volume ratios. However, achieving precise pore-size regulation remains a critical challenge in membrane design. Herein, we report a defect-engineering strategy for COF membranes through in-situ polydopamine (PDA) incorporation during interfacial polymerization. Dopamine undergoes oxidative self-polymerization in the p -phenylenediamine (Pa) aqueous phase, generating PDA that simultaneously reacts with Pa monomers and infiltrates TpPa-COF framework defects via Schiff-base chemistry. This dual-function modification not only repairs structural imperfections, but also introduces hydrophilic moieties that enhance surface wettability. The optimized PDA-TpPa membrane demonstrates superior separation performance, achieving 99 % rejection of organic dyes while maintaining a high water permeance of 117.3 L m −2  h −1 bar −1 . Furthermore, the membrane exhibits considerable permeance towards various organic solvents, notably for n-hexane, which reached as high as 337 L m −2  h −1 bar −1 . This work establishes a novel paradigm for fabricating high-performance COF membranes.