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.