Liquid–liquid–solid interfacial polymerization approach to rapid fabrication of large-sized, self-standing structured COF membranes†

Covalent organic framework (COF) membranes, with their customizable chemical structures and regular nanochannels, are widely used for separation. However, challenges remain in the rapid and high-yield fabrication of robust, self-standing, flexible, large-sized, highly crystalline COF membranes, especially as self-standing or supported membranes. Here, we introduce a liquid–liquid–solid interfacial polymerization technique at high temperature for the rapid production (in a few hours) of large-sized, robust, flexible, and thickness-adjustable highly crystalline self-standing all COF membranes with hierarchical structure in which a nano COF membrane is integrated on COF hollow fiber networks of the same material, achieving impressive mechanical stability (tensile strength ∼23 MPa), which is maintained even after 500 bending cycles and 80% compression. Furthermore, we demonstrate the universality of this technique by preparing various imine-linked COFs on different porous substrates. Laboratory filtration experiments produced excellent results, highlighting the considerable potential of COF membranes for use in industrial wastewater purification applications going forward.