Krypton/Xenon separation at room temperature in a flexible coordinative framework sorbent.

Abstract

The separation of xenon from krypton holds significant importance across various fields, including high-tech industries, national defence, and aerospace. Adsorptive separation via porous solids is considered one of the most promising alternatives to conventional energy-intensive cryogenic processes. While traditional adsorbents selectively capture xenon over krypton under ambient conditions, their desorption energy penalties for producing pure xenon impede practical implementation. Here, we present a metal‒organic framework characterized by synergistic structural and local flexibility that reverses conventional selectivity, thereby enabling preferential adsorption of krypton at room temperature. This material demonstrates a krypton uptake of 36.8 cm³cm^-3 (298 K, 1 bar) and achieves a Kr/Xe selectivity of 10.4 in 1/99 Kr/Xe mixture breakthrough experiments. Moreover, this material exhibits commendable radioactive stability and effectively captures trace amounts of krypton (40 ppm). Mechanistic studies indicate that dynamic adjustments in cavity windows and localized ligand vibrations work synergistically to exploit subtle size differences between krypton and xenon. This enables kinetically controlled sieving of krypton through transiently expanded channels. With an energy-efficient approach to krypton-centric separation, our research redefines the design paradigm for noble gas purification and offer new possibilities for separating other dynamically matched molecules through adaptive host‒guest interactions.