High-performance COF membranes prepared by an in-situ interfacial polymerization for effective pharmaceutical fractionation

Organic solvent nanofiltration (OSN) provides an energy-efficient approach for pharmaceutical fractionation, but its broader implementation is restricted by the inherent permeability–selectivity trade-off. Here, we report a COF membrane fabricated through an in-situ interfacial polymerization (IP) strategy. Unlike conventional IP, this in-situ method enables direct COF growth on a porous support or via a COF interlayer, eliminating transfer steps and ensuring robust adhesion. By tuning the polymerization temperature, the membrane thickness can be precisely regulated, resulting in high rejection of vitamin B12, rifampicin, and eriochrome black T (95.4–99.0%) while maintaining permeation of their respective precursors of 5,6-dimethylbenzimidazole, 1-amino-4-methylpiperazine, and 4-nitrophenol (8.8–15.3%). The interlayer architecture preserves the rejection performance while doubling the solvent permeance (e.g., methanol: 21.7 → 42.8 L m -2 h -1 bar -1 ) and increasing the pharmaceutical mixture processing rates. Overall, this work establishes a sequential in-situ IP route for versatile COF membrane fabrication and demonstrates that a COF interlayer design can effectively mitigate the long-standing OSN permeability–selectivity trade-off, enabling high-flux and high-efficiency pharmaceutical separations. • COF membranes are fabricated via in-situ interfacial polymerization • They are directly formed on a substrate or via a COF interlayer • The membrane with an interlayer doubled its permeance at a similar rejection. • High-flux fractionation effectively separates pharmaceuticals from precursors