Single‐Phase Covalent Organic Framework Staggered Stacking Nanosheet Membrane for CO 2 ‐Selective Separation

Abstract Two‐dimensional covalent organic frameworks (2D COFs) are considered as potential candidates for gas separation membranes, benefiting from permanent porosity, light‐weight skeletons, excellent stability and facilely‐tailored functionalities. However, their pore sizes are generally larger than the kinetic diameters of common gas molecules. One great challenge is the fabrication of single‐phase COF membranes to realize precise gas separations. Herein, three kinds of high‐quality β‐ketoenamine‐type COF nanosheets with different pore sizes were developed and aggregated to ultrathin nanosheet membranes with distinctive staggered stacking patterns. The narrowed pore sizes derived from the micro‐structures and selective adsorption capacities synergistically endowed the COF membranes with intriguing CO 2 ‐philic separation performances, among which TpPa‐2 with medium pore size exhibited an optimal CO 2 /H 2 separation factor of 22 and a CO 2 permeance of 328 gas permeation units at 298 K. This membrane performance reached the target with commercial feasibility for syngas separations.