Molecular Probing in a Metal-Organic Framework for Selective Gas Adsorption and Separation

Metal-organic frameworks (MOFs) hold significant potential for selective gas adsorption and separation. However, it remains challenging to experimentally reveal collective host-guest interactions and cooperative binding sites at the atomic level in nanosized MOFs and thereby rationalize their separation preferences. Here, we report a molecular probing strategy combined with cryo-3D ED for guiding the selective gas adsorption and separation in MOFs. Molecular probes were purposefully selected to map the binding domains of gas adsorbates in the candidate MOF via atomic-level structural analysis by cryo-3D ED, thereby rationalizing which separation scenario the MOF is most likely to favor. As an example, CO₂ and Xe probes reveal multiple host-guest interactions in a reported MOF SU-100, including van der Waals force, coordination bonds, and dipole-dipole interactions. Additional adsorption sites based on cooperative dual open metal sites were detected, enabling extra adsorption of gas molecules with a B^δ--A^δ+-B^δ- configuration. Based on above results, the MOF shows remarkable performance for adsorbing SO₂, i.e., high uptake, excellent stability, and effective removal of trace SO₂ in the presence of CO₂ and N₂, which is of great importance in the desulfurization of flue gas toward CO₂ capture and recycling.