Interfacial Polymerization of Self-Standing Covalent Organic Framework Membranes at Alkane/Ionic Liquid Interfaces for Dye Separation

Covalent organic frameworks (COFs) are a promising candidate for advanced water treatment membranes due to their numerous benefits, such as adjustable pore diameters, high crystallinity, chemical stability, and a well-organized channel structure. Liquid–liquid interfacial polymerization is an effective method for COF membrane synthesis owing to its comparatively milder reaction conditions and efficient collection of products from the reaction system. However, the fabrication of continuous COF membranes at a non-alkane/water interface remains a formidable task due to membrane flaws caused by solvent evaporation and the restriction of water-soluble monomers. At the alkane/ionic liquid interface, we synthesized two self-standing, flexible, imine-linked COF membranes with different thicknesses and morphologies. The ionic liquid as a solvent can dissolve various amines, and polyamide nanofilms can be formed by the intermolecular reaction between amines and trimesoyl chloride. The freestanding ultrathin selective membrane is created with continuous, defect-free, and vast areas of up to 2 cm in diameter wafer-scale pore sizes as ultrafast molecular sieving. The membrane exhibited an extremely high water flow of 67.37 L m –2 h –1 bar –1 as well as an excellent rejection (98.7% for methylene blue). The resulting polyamide nanofilms displayed ultrahigh water permeability and good dye rejection selectivity.