Dual-Wing Ligand Constructed Metal-Organic Framework Membranes with Finely Tuned Apertures for Natural Gas Separation

Abstract Metal-organic framework (MOF) membranes with apparent molecular sieving effect have great potential for gas separation. However, their application in light-gas separation (e.g. CO2/CH4 and H2/CH4) remains challenging due to their enlarged pore structures under transmembrane pressure. In this work, we report a series of MOF membranes constructed from dual-wing (DW) ligands including 2-chloromethylbenzimidazole, 2-methylbenzimidazole, 2-ethylbenzimidazole, and 2-phenylbenzimidazole, to finely tune apertures and enhance molecule sieving property for small-size gases. These DW-ligands provide steric resistance in two directions perpendicular to the coordination bond, leading to a much finer pore structure. The introduction of the DW-ligands endows the DW/ZIF-8 membranes with an adjustable bottleneck door for regulating gas diffusion, blocking the transport of large-size CH4 while allowing small-size CO2 to permeate. The membranes show significantly improved molecular sieving property with separation factor of CO2/CH4 above 55 in the case of 2-chloromethylbenzimidazole23/ZIF-8 membrane, which represents the highest value among the reported MOF membranes. The membrane also exhibits exceptional separation performance for H2/CH4 and H2/C3H8 with separation factors of 430 and 34341, surpassing most of the reported MOF membranes. This study presents a facile and efficient strategy for regulating MOF aperture and constructing high-performance membranes for natural gas separation.