Tailoring Pore Environments in Metal-Organic Frameworks for Efficient C2H2/CO2 and C2H2/C2H4 Separations

The efficient separation of acetylene (C2H2) from carbon dioxide (CO2) and ethylene (C2H4) is of significant industrial importance but remains highly challenging due to their similar physicochemical properties. In this study, three isostructural metal-organic frameworks, [Co4(mu 4-SO4)2(tpim)2(L)2] (tpim = 2,4,5-tri(4-pyridyl)-imidazole, L = dicarboxylate; termed as Co4-L), are constructed from sulfate-capped Co4 clusters extended by N-rich tpim linkers and different-sized dicarboxylate ligands. Among them, the Co-4-1,4-ndc framework, incorporating 1,4-naphthalenedicarboxylic acid (1,4-ndc), offers optimal pore confinement that promotes host-guest interactions between C2H2 molecules and framework. This material exhibits high C2H2 capture capacities of 4.30 and 3.40 mmol g-(1) from equimolar C2H2/CO2 and C2H2/C2H4 mixtures, respectively. Theoretical simulations reveal that the enhanced selectivity arises from multiple cooperative hydrogen-bonding interactions between C2H2 and the framework Co-4-1,4-ndc, generating strong and preferential binding sites. This study highlights the role of pore-environment engineering of metal-organic frameworks (MOFs) for selective C2H2 separation, providing a foundation for the development of advanced adsorbents in industrial gas purification.