A highly connected metal–organic framework with a specific nonpolar nanotrap for inverse ethane/ethylene separation

Abstract

Efficient separation of ethylene (C₂H₄) from ethane (C₂H₆) via a one-step adsorption process is desirable yet challenging. In this work, we report a C₂H₆-selective polynuclear Tb-MOF [Tb₉(μ₃-O)₂(μ₃-OH)₁₂(H₂O)₉(TCPE)₃]⁻·[H₃O]⁺·(solvents)_x (TCPE = tetrakis(4-carboxyphenyl)ethylene acid), NKU-200-Tb, assembled via the reticular chemistry principle. The resulting (4,12)-connected framework critically features a high density of nonpolar aromatic rings on the pore surface and forms a specific nanotrap for C₂H₆ with multiple C–H⋯π interaction sites. As a result, NKU-200-Tb exhibits an inverse adsorption behavior with a high C₂H₆/C₂H₄ selectivity of 2.06 and a large uptake ratio of 151% (60.27/39.95 cm³ g⁻¹) at 298 K and 1 bar. The superior adsorption properties of NKU-200-Tb, combined with great structural stability, place it among the most promising stable C₂H₆-selective MOFs. Dynamic breakthrough experiments demonstrate that polymer-grade C₂H₄ (>99.9%) can be harvested in one step from a binary mixture of C₂H₆/C₂H₄ (10/90, v/v). This work signifies the synergy of pore surface chemistry and space confinement in promoting the challenging C₂H₆/C₂H₄ separation.