Cage-Interconnected Metal–Organic Framework with Tailored Apertures for Efficient C₂H₆/C₂H₄ Separation under Humid Conditions

Abstract

Metal-organic frameworks (MOFs) with open metal sites (OMSs) have been shown to preferentially adsorb unsaturated hydrocarbons such as C₂H₄ due to the formation of π-complexation. However, the adsorption capacity and selectivity might well be dampened under humid conditions because OMSs could be easily poisoned in the presence of water vapor. C₂H₆-selective adsorbents with less hydrophilic environments, on the other hand, not only could effectively minimize the impact of humidity on separation capacity but also could directly produce high-purity C₂H₄ from C₂H₆/C₂H₄ mixtures. Here, we report a C₂H₆-selective MOF (<b>JNU-2</b>) underlying a rare <b>xae</b> topology. Its cage-like cavities are interconnected through apertures with a limiting diameter of ca. 3.7 Å, which is in the domain of kinetic diameters of C₂H₄ and C₂H₆ molecules. Molecular modeling studies suggest the four oxygen atoms on aperture are poised to preferentially interact with C₂H₆ through multiple C-H···O hydrogen bonding, rendering <b>JNU-2</b> an enhanced C₂H₆ selectivity. Indeed, experimental results reveal that <b>JNU-2</b> not only takes up a great amount of C₂H₆ comparable to other top-performing C₂H₆-selective MOFs but also displays excellent separation capacity even under humid conditions; moreover, it can be easily regenerated at room temperature owing to its moderate adsorption enthalpy. This work successfully demonstrated a strategy of balancing adsorption capacity and selectivity for C₂H₆ by designing MOF materials with cavities interconnected through tailored apertures. The apertures function as screening sites for C₂H₆ selectivity, while the internal cavities provide space for large adsorption.