Dynamic Xe Recognition-Resonance-Capture Mechanism in Tröger's Base Dihedral Angle for Efficient Xe/Kr Separation

This study addresses the critical challenge of Kr coadsorption during Xe/Kr separation in rigid porous adsorbents by developing novel flexible porous adsorbents based on Tröger's Base dihedral angle structures (TBPOF-1 to TBPOF-4). These TBPOFs leverage a flexible dihedral angle that dynamically adapts to selectively capture Xe over Kr through a "recognition-resonance-capture" mechanism. The adsorbents exhibit exceptional Xe uptake capacities with negligible Kr adsorption at pressures below 0.2 bar, achieving a record IAST selectivity of 483.8 (for Xe/Kr = 50:50 at 0.01 bar with TBPOF-4). Adsorption kinetic studies reveal rapid Xe adsorption (10.4 mL g^-1 s^-1) compared to sluggish Kr uptake (0.10 mL g^-1 s^-1) in TBPOFs, yielding a kinetic selectivity of 1166. Breakthrough experiments demonstrate that TBPOFs enable one-step Xe purification without Kr coadsorption, achieving >99.9% Xe and Kr in a one-step adsorption-desorption process, even at trace Xe-Kr concentration (400 ppm Xe, 40 ppm Kr) mixed-gas flows. Density functional theory and molecular dynamics (DFT/MD) simulations elucidate the dynamic Xe "recognition-resonance-capture" mechanism of the Tröger's Base dihedral angle. This work offers a transformative strategy to design dynamic Xe recognition adsorbents for energy-efficient Xe-Kr separation.