Balancing uptake and selectivity in a copper-based metal–organic framework for xenon and krypton separation

Efficient separation of Xenon (Xe) and krypton (Kr) is important in the gas industries but remains challenging. Adsorptive separation affords an energy-efficient method to isolate the two noble gases, yet developing selective adsorbents with high uptake and excellent selectivity remains difficult, limited by a trade-off between uptake and selectivity. We report MOF-11 with optimal pore size and accessible open metal sites (OMSs) for separation of Xe over Kr via the discriminable difference in van der Waals interactions. MOF-11 affords a new benchmark for Xe/Kr separation with high Xe uptakes of 4.05 and 4.95 mmol/g (at 0.2 and 1 bar), high Xe/Kr Henry and IAST selectivity (13.6 and 16.1) at 298 K. Evidenced by Xe-loaded structure, multiple Xe···H interactions between Xe and the terminal H atoms allow Xe atoms firmly packed within the framework. This work demonstrates a strategy for balancing uptake and selectivity in Xe/Kr separation by capitalizing on the synergy between optimal pore size and OMSs.