Asymmetric recognition in metal-organic frameworks for enhanced ethylene/ethane sieving

Ethylene/ethane (C₂H₄/C₂H₆) separation is one of the most energy-intensive processes in the petrochemical industry, highlighting the urgent need for efficient adsorbents to replace cryogenic distillation. In this work, a new metal-organic framework (MOF), TYUT-25, is constructed via an asymmetric recognition strategy to achieve directional regulation of adsorption behavior within channels. In conventional systems, structural modulation typically induces a synchronous adsorption response, where C₂H₄ and C₂H₆ uptake increase or decrease simultaneously, thereby limiting further improvements in selectivity. In contrast, the asymmetric recognition strategy results in inverse adsorption behaviors of C₂H₄ and C₂H₆. The pore aperture is contracted to suppress C₂H₆ entry, thereby enabling size-sieving discrimination between C₂H₄ and C₂H₆, while the pore cavity enhances interactions between C₂H₄ and the framework, leading to enhanced C₂H₄ uptake and suppressed C₂H₆ adsorption. Compared with Zn(BPA)(BDC), adsorption measurements show that the C₂H₄ uptake of TYUT-25 increases from 1.6 to 8.4 cm³ g^-1 at 0.1 bar and reaches 34.4 cm³ g^-1 at 1 bar. At 298 K and 1 bar, the C₂H₄/C₂H₆ selectivity exceeds 10⁴. Breakthrough experiments further verify separation performance. DFT calculations and Hirshfeld surface analysis indicate enhanced host-guest interactions. This work demonstrates that asymmetric recognition enables inverse adsorption responses, providing an effective strategy for the coordinated regulation of adsorption capacity and selectivity within a MOF.