Fluorinated Covalent Organic Framework Membranes Enable High‐Efficiency and Water‐Resistance CO 2 /N 2 Separation

Abstract Membrane separation is advantageous in mitigating excessive carbon dioxide (CO 2 ) emission of worldwide concern. However, most membranes are vulnerable to water during CO 2 separation from combustion disposal gas, resulting in performance deterioration. Water‐resistant covalent organic framework (COF) membranes for efficient CO 2 separation from wet gas stream are designed and synthesized. Two COFs termed as COF‐TpPa‐1‐CF 3 and COF‐TFBPa‐CF 3 are constructed using planar trifluoromethyl‐functionalized monomers; featuring open straight pores, high hydrophobicity, and unique CO 2 affinity. Liquid–liquid interfacial polymerization renders the self‐standing COF membranes free of cracks. COF‐TFBPa‐CF 3 and COF‐TpPa‐1‐CF 3 membranes are able to separate CO 2 from N 2 under dry and wet conditions; and the former membrane is more resistant against water than the latter one, demonstrated by invariant gas permeation. The COF‐TFBPa‐CF 3 membrane exhibits exceptional CO 2 permeability (>9000 Barrer) and high CO 2 /N 2 selectivity (>25), superior to other reported COF membranes. Moreover, the selectivity‐permeability product breaks 2008 upper bound. The excellent separation performance, water stability, and high reproducibility promise COF‐TFBPa‐CF 3 membrane in practical CO 2 separation from post‐combustion gas.