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

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.