From Global Flexibility to Local Flexibility: Enable A-B Stacked Metal-Organic Framework for One-Step Ethylene...

Flexible metal-organic framework (MOF) adsorbents can achieve exceptional separation performances under appropriate stimuli, especially for complex gas mixtures. However, their intrinsic global flexibility often leads to unsatisfactory separation selectivity, which hampers the practical applications. Herein, we propose a "rotor-locker" strategy to convert an A-B stacked Cd-MOF-GF (GF = global flexibility) into Cd-MOF-LF (LF = local flexibility) for efficient one-step C₂H₄ separation from multiple complex gas mixtures. The grafted methyl groups serve as lockers to suppress global flexibility while preserving local stimulus-responsive behavior. As a result, Cd-MOF-LF exhibits a 10-fold increase in C₂H₂ uptake (1.95 mmol g^-1) compared to Cd-MOF-GF (0.19 mmol g^-1) at 0.1 bar and 298 K, yielding a record selectivity of 9.2 for C₂H₂/C₂H₄ (50/50) among similar adsorbents. Moreover, the selective capture of C₂H₆ and CO₂ impurities is also significantly enhanced. Dynamic breakthrough experiments demonstrate that the Cd-MOF-LF column enables direct separation of polymer-grade C₂H₄ (>99.9%) with a high productivity of 0.79 mmol g^-1 from a quaternary C₂H₂/C₂H₆/CO₂/C₂H₄ (1v/33v/33v/33v) gas mixture. Density functional theory calculations reveal a lower deformation energy (-3.99 kJ mol^-1) and specific adsorption sites for Cd-MOF-LF.