Vertical covalent organic framework interlayer channels enable ultraselective molecular separations

This work addresses the long-standing challenge of insufficient permselectivity in two-dimensional (2D) covalent organic framework (COF) membranes by developing a generalizable and potentially scalable self-templating interfacial assembly method to synthesize vertically aligned 2D COF polycrystalline nanofilms. Experiments and molecular simulations reveal that molecular amphiphilicity-driven spontaneous confinement and directional alignment of framework-building units at the organic/aqueous interface instigate the vertical growth of COF monolayers. The superior sieving ability of sub–4 angstrom interlayer nanochannels enables vertically aligned COF membranes to efficiently intercept salt ions, electrically neutral small molecules, and hazardous chemicals, outperforming conventional COF membranes. The implemented strategy can be extended to other building blocks and framework topologies, opening up avenues for fine-tuning the pore structure of 2D COF membranes.