Fluorinated Covalent Organic Framework Membranes Enable High‐Efficiency and Water‐Resistance CO₂/N₂ Separation

Abstract Membrane separation is advantageous in mitigating excessive carbon dioxide (CO₂) emission of worldwide concern. However, most membranes are vulnerable to water during CO₂ separation from combustion disposal gas, resulting in performance deterioration. Water‐resistant covalent organic framework (COF) membranes for efficient CO₂ separation from wet gas stream are designed and synthesized. Two COFs termed as COF‐TpPa‐1‐CF₃ and COF‐TFBPa‐CF₃ are constructed using planar trifluoromethyl‐functionalized monomers; featuring open straight pores, high hydrophobicity, and unique CO₂ affinity. Liquid–liquid interfacial polymerization renders the self‐standing COF membranes free of cracks. COF‐TFBPa‐CF₃ and COF‐TpPa‐1‐CF₃ membranes are able to separate CO₂ from N₂ 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‐CF₃ membrane exhibits exceptional CO₂ permeability (>9000 Barrer) and high CO₂/N₂ 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‐CF₃ membrane in practical CO₂ separation from post‐combustion gas.