Pore engineering in double-wall MOFs through immobilizing functional bonding sites for boosting efficient ethane/ethylene separation

Abstract

In the petrochemical industry, the efficient one-step adsorption separation of ethylene (C₂H₄) and ethane (C₂H₆) is a favored but challenging technical task. This highlights the importance of upgrading functional group design standards to create physical adsorbent materials that combines superior C₂H₆ adsorption capacity and excellent C₂H₆/C₂H₄ selectivity to meet the demanding needs of industry. Herein, we presented a strategy that tuning the pore environment of nonpolar metal–organic frameworks (MOFs) via installing additional polar functional binding sites in the pores to boost C₂H₆/C₂H₄ separation performance. By introducing methyl and fluorine as functional sites into carboxylic ligands, we successfully designed and synthesized two novel MOFs, named GNU-3-Me and GNU-3-F. The pore size and physical and chemical properties of the two MOFs were carefully regulated. We found that the GNU-3-F has an optimized aperture and pore surface environment, with a high C₂H₆ uptake (92.55 cm³ cm⁻³ at 1 bar and 298 K) and an outstanding equimolar C₂H₆/C₂H₄ selectivity (2.1), superior to most C₂H₆ selective MOFs. Computational studies show this excellent C₂H₆ absorption capacity and selectivity in GNU-3-F mainly roots in its well-designed pore size and fluorine modified pore environment. These properties work together to significantly improve its affinity and distinguish ability to C₂H₆ molecules in GNU-3-F. The breakthrough experiments finally demonstrate that GNU-3-F can efficiently separate C₂H₆/C₂H₄ mixtures under ambient conditions.