Interfacial polymerization of covalent organic frameworks (COFs) on polymeric substrates for molecular separations

Covalent organic frameworks (COFs) represent a new family of porous polymers with highly ordered two or three-dimensional channels. Although numerous studies have been focused on the design and synthesis of COF in the form of powders, the development of COF-based separation membranes is still hampered by the challenges of COF particles agglomeration and harsh synthetic conditions. In this work, interfacial polymerization (IP) directly performed on polymeric substrates as employed in the traditional IP process of polyamide (PA) membranes is developed for the synthesis of COF-based membranes. With the moderate reaction rate between monomer pairs in corresponding aqueous and organic solutions, a conformal growth of COF crystallites directly composited with the polysulfone (PSF) ultrafiltration substrates can be realized within 1 min. The synthesis parameters including reaction time and precursor concentrations are optimized, and thus-synthesized COF/PSF membrane presents a stable rejection to dye (Congo red) of 99.5% with a high water permeance of up to 50 L m⁻² h⁻¹ bar⁻¹, which is 2–10 times higher than that of many other membranes with similar rejection. This convenient IP process is expected to facilitate the up-scaling and real-world applications of COF-based membranes.