Summary
A research group consisting of Dr. Takashi Yanase of the Department of Chemistry, Faculty of Science, Toho University, and members of the Graduate School of Chemical Sciences and Engineering, Hokkaido University, have successfully synthesized covalent organic framework (COF) films with a nanoscale thickness control, via a novel deposition polymerization technique called as alternate deposition. In this method, a precise control over the ratio of the two precursor molecules during the deposition process results in robust COF films with high chemical resistance and mechanical strength. The synthesized COF films can be easily peeled off from the substrate and used as free-standing films. The COF membrane has numerous nanometer-sized micropores, which can be used to separate gas mixtures. In this study, the synthesized COF membrane was utilized in the separation of CO₂ and N₂. The amount of CO₂ that permeated through the membrane was more than four times that of N₂, indicating that the membrane was highly selective and effective in separating CO₂ from the mixture. Quantum chemical calculations revealed that this high selectivity was not due to the gate effect, but rather due to the intermolecular forces between CO₂ and the carbonyl groups in the micropores of the COF membrane. The results of this research were published online in ACS Applied Nano Materials on Wednesday, February 2, 2022.