Ultramicroporous Metal–Organic Framework Featuring Multiple Polar Sites for Efficient Xenon Capture and Xe/Kr Separation

Efficient adsorption separation of xenon/krypton (Xe/Kr) mixtures is an important technological challenge due to their similar sizes and shapes. Herein, we report an ultramicroporous metal–organic framework (MOF), ZJU-Bao-302a, with pore sizes close to the kinetic diameter of Xe and pore surfaces lined with a high density of polar sites, including methyl groups, amines, and uncoordinated oxygen atoms. The synergistic effect of these polar sites enables ZJU-Bao-302a to exhibit a high Xe uptake of 2.77 mmol g–1 and a balanced Xe/Kr selectivity of 14.6 under ambient conditions. Dynamic breakthrough experiments demonstrate the material's capability to efficiently separate Xe/Kr mixtures (20/80) as well as capture Xe at ultralow concentrations (400 ppmv) from nuclear reprocessing exhausts, achieving a superior dynamic Xe capacity of 24.2 mmol kg–1. Density functional theory calculations reveal that the localized polar groups/atoms in ZJU-Bao-302a provide more effective recognition sites for Xe than Kr, enhancing the thermodynamic selectivity. This study highlights the importance of integrating tailored pore sizes and dense polar sites in metal–organic frameworks for developing high-performance Xe/Kr separation adsorbents.