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

Efficient extraction of high-purity CO from humid flue gas via adsorptive separation offers a promising and sustainable solution for carbon reduction and downstream applications. However, the coadsorption of HO vapor and N 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 CO 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 HO barriers and CO channels on the outer shell while maintaining pore integrity in the core. The resulting core-shell material demonstrates exceptional CO adsorption capacity and an extraordinary CO/N selectivity of 1780 (15/85, v/v), surpassing conventional adsorbents. Notably, dry CO 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 HO barriers, while ionic liquid segments facilitate the transport of CO 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.