Flexible covalent organic framework membranes with linear aliphatic amines for enhanced organic solvent nanofiltration

Abstract

Covalent organic framework (COF) based membranes hold great promise for organic solvent nanofiltration (OSN) due to their unique molecular arrangement, well-defined porous network, and broader solvent tolerance. However, scaling up their fabrication on porous supports without compromising these properties presents many challenges. In this study, COF membranes are fabricated on a porous support using liquid–liquid interfacial polymerization. The pore size and chemistry of the COF membranes are rationally modified by covalently bridging different aliphatic diamines with varying amine groups. The growth process of the COFs nanofilm is thoroughly studied using morphology and chemical structures analysis, which confirms β-ketoenamine bond formation between both monomers. Next, the COFs film is transferred to a porous support and thoroughly investigated before its application in OSN. The fabricated COF membranes display superior solvent permeance and precise molecular separation compared to conventional nanofiltration membranes. They also demonstrate substantial fouling resistance in both static and dynamic conditions. Furthermore, the COF membranes show good operational stability when subjected to continuous solvent permeation for 24 h without any surface defects or disruption in permeation activity. These results demonstrate the potential for synthesizing linear aliphatic diamine-based COFs and their membranes via facile liquid–liquid interfacial polymerization for various membrane filtration applications.