Ionic Hydrophobic Gates on Metal–Organic Frameworks Enable High-Purity CO2 Separation from Humid Flue Gas

Efficient extraction of high-purity CO₂ from humid flue gas via adsorptive separation offers a promising and sustainable solution for carbon reduction and downstream applications. However, the coadsorption of H₂O vapor and N₂ from humid flue gas remains a persistent challenge that limits separation efficiency. To overcome this issue, this work introduces a novel concept of ionic hydrophobic gates on porous adsorbents, which enables one-step separation of high-purity CO₂ directly from humid flue gas. By assembling hydrophobic ionic liquids and fluorine-rich terephthalaldehyde onto the surface of a metal-organic framework (MOF), this design establishes H₂O barriers and CO₂ channels on the outer shell while maintaining pore integrity in the core. The resulting core-shell material demonstrates exceptional CO₂ adsorption capacity and an extraordinary CO₂/N₂ selectivity of 1780 (15/85, v/v), surpassing conventional adsorbents. Notably, dry CO₂ with 99.999% purity is successfully extracted from humid flue gas (relative humidity, RH = 100%) in a single breakthrough experiment. In situ diffuse reflectance Fourier transform infrared spectroscopy (in situ DRIFTS) and density functional theory calculations reveal that fluorine-rich hydrophobic sites act as effective H₂O barriers, while ionic liquid segments facilitate the transport of CO₂ through hydrogen bonding and electrostatic interactions. Owing to its excellent scalability and broad compatibility with diverse MOF platforms, this ionic hydrophobic gating strategy offers a robust and versatile approach for constructing advanced gas separation materials, holding great promise for industrial applications in carbon capture, clean energy, and sustainable chemical processes.