Microporous Metal–Organic Framework with Cage-within-Cage Structures for Xenon/Krypton Separation

Separation of Xe/Kr mixtures is of high significance but a daunting task in the chemical industry because of the inert physicochemical properties and similar kinetic diameters of Xe and Kr. Herein, a water-resistant metal–organic framework (MOF) JXNU-11(Fe2Ni) features distinctive cage-within-cage structures with small octahedral cages encapsulated in large cuboctahedral cages. JXNU-11(Fe2Ni) displays a high Xe uptake capacity of 124 cm3 g–1 at 273 K. The breakthrough interval between Xe and Kr for Xe/Kr (20/80) mixtures is 56 min g–1 at 273 K, making JXNU-11(Fe2Ni) one of the highest-performing MOF. Additionally, JXNU-11(Fe2Ni) exhibits high Xe productivity for high-purity Xe, good recycling performance, and low regeneration energy in breakthrough experiments. Computational simulations on JXNU-11(Fe2Ni) indicate that the preferential site for Xe is the interlayered spaces between the octahedral cage and the cuboctahedral cage. The Xe atom is firmly trapped through extensive Xe···framework interactions. Thus, the high water stability, high productivity of highly pure Xe, good recyclability, and low regeneration energy of JXNU-11(Fe2Ni) render it a promising adsorbent for actual Xe/Kr separation.