Interfacial polymerization of COF-polyamide composite membranes modified with ionic liquids for CO2 separations

Abstract

Covalent organic frameworks (COFs), characterized by their well-organized porous structure, exhibit promising prospects for carbon capture. Nevertheless, their weak film-forming property and relatively large pore sizes constrain their utilization as gas separation membranes. This study introduced a facile approach to fabricating COF membranes tailored for CO₂ separations. By introducing an extra monomer, trimesoyl chloride (TMC), together with COF monomers, a thin and defect-free layer of COF-polyamide was synthesized by interfacial polymerization process. The amide structure embedded into the COFs layers was expected to mend the defects, strengthen the binding forces, and improve the stability of the COFs layers. To further enhance the performance, imidazolium ionic liquid (IL) was adopted to modify the COF-polyamide layer. The introduction of TMC rendered the COF-polyamide layer more negatively charged, facilitating stronger binding to the positively charged cations in the IL. This modification with IL effectively reduced the pore size of the COFs and increased the affinity for CO₂. The resultant COF composite membranes exhibited a high CO₂ permeance of 125.9 GPU and CO₂/N₂ selectivity up to 35.0, accompanied by robust long-term stability. Our method paves a new way for the fabrication and application of interfacial polymerized COF membranes for gas separation applications.