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 C 2 H 4 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. C 2 H 6 -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 C 2 H 4 from C 2 H 6 /C 2 H 4 mixtures. Here, we report a C 2 H 6 -selective MOF ( JNU-2 ) underlying a rare xae 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 C 2 H 4 and C 2 H 6 molecules. Molecular modeling studies suggest the four oxygen atoms on aperture are poised to preferentially interact with C 2 H 6 through multiple C–H···O hydrogen bonding, rendering JNU-2 an enhanced C 2 H 6 selectivity. Indeed, experimental results reveal that JNU-2 not only takes up a great amount of C 2 H 6 comparable to other top-performing C 2 H 6 -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 C 2 H 6 by designing MOF materials with cavities interconnected through tailored apertures. The apertures function as screening sites for C 2 H 6 selectivity, while the internal cavities provide space for large adsorption.