Rationally designed tetrahedral-configuration-matching methane trap in a metal–organic framework for efficient CH4/N2 separation

Abstract

The enrichment and purification of CH₄ from coalbed methane by adsorption are important but challenging. We propose a “tetrahedral-configuration-matching” metal–organic framework (MOF) methane trap, TUTJ-3Ni, with cyclopropyl groups precisely positioned to create a pre-configured pore structure that is geometrically complementary to tetrahedral CH₄ molecules. TUTJ-3Ni exhibits a substantially higher CH₄ adsorption heat (30.3 kJ mol⁻¹) than its analogue TUTJ-2Ni (24.0 kJ mol⁻¹), and this value is the highest among reported adsorbents. Moreover, TUTJ-3Ni exhibits a superior CH₄/N₂ selectivity of 11.1, the highest value reported for hydrophobic MOFs. In situ spectroscopy and theoretical modeling results elucidate that the matched tetrahedral binding pocket, constructed with two hydrogen atoms of the cyclopropyl group along with fluorine and oxygen atoms from the ligand, engages all four hydrogen atoms of CH₄ via synergistic van der Waals interactions. Breakthrough experiment results verify that TUTJ-3Ni delivers high-purity CH₄ (>99.9%) from coalbed methane and that its dynamic CH₄ working capacity in humid environments is the highest among reported adsorbents. Furthermore, TUTJ-3Ni has good thermal and moisture stability and can easily be scaled up, making it promising for potential industrial applications.