Ultramicroporous\nMetal–Organic Framework Featuring\nMultiple Polar Sites for Efficient Xenon Capture and Xe/Kr Separation

Efficient adsorption separation of xenon/krypton (Xe/Kr)\nmixtures\nis an important technological challenge due to their similar sizes\nand shapes. Herein, we report an ultramicroporous metal–organic\nframework (MOF), ZJU-Bao-302a, with pore sizes close to the kinetic\ndiameter of Xe and pore surfaces lined with a high density of polar\nsites, including methyl groups, amines, and uncoordinated oxygen atoms.\nThe synergistic effect of these polar sites enables ZJU-Bao-302a to\nexhibit a high Xe uptake of 2.77 mmol g<sup>–1</sup> and a\nbalanced Xe/Kr selectivity of 14.6 under ambient conditions. Dynamic\nbreakthrough experiments demonstrate the material’s capability\nto efficiently separate Xe/Kr mixtures (20/80) as well as capture\nXe at ultralow concentrations (400 ppmv) from nuclear reprocessing\nexhausts, achieving a superior dynamic Xe capacity of 24.2 mmol kg<sup>–1</sup>. Density functional theory calculations reveal that\nthe localized polar groups/atoms in ZJU-Bao-302a provide more effective\nrecognition sites for Xe than Kr, enhancing the thermodynamic selectivity.\nThis study highlights the importance of integrating tailored pore\nsizes and dense polar sites in metal–organic frameworks for\ndeveloping high-performance Xe/Kr separation adsorbents.