Switchable Xe/Kr Selectivity in a Hofmann‐Type Metal–Organic Framework via Temperature‐Responsive Rotational Dynamics

Abstract

AbstractThe development of adsorbents for Kr and Xe separation is essential to meet industrial demands and for energy conservation. Although a number of previous studies have focused on Xe‐selective adsorbents, stimuli‐responsive Xe/Kr‐selective adsorbents still remain underdeveloped. Herein, a Hofmann‐type framework Co(DABCO)[Ni(CN)4] (referred to as CoNi‐DAB; DABCO = 1,4‐diazabicyclo[2,2,2]octane) that provides a temperature‐dependent switchable Xe/Kr separation performance is reported. CoNi‐DAB showed high Kr/Xe (0.8/0.2) selectivity with significant Kr adsorption at 195 K as well as high Xe/Kr (0.2/0.8) selectivity with superior Xe adsorption at 298 K. Such adsorption features are associated with the temperature‐dependent rotational configuration of the DABCO ligand, which affects the kinetic gate‐opening temperature of Xe and Kr. The packing densities of Xe (2.886 g cm−3 at 298 K) and Kr (2.399 g  cm−3 at 195 K) inside the framework are remarkable and comparable with those of liquid Xe (3.057 g cm−3) and liquid Kr (2.413 g cm−3), respectively. Breakthrough experiments confirm the temperature‐dependent reverse separation performance of CoNi‐DAB at 298 K under dry and wet (88% relative humidity) conditions and at 195 K under dry conditions. The unique adsorption behavior is also verified through van der Waals (vdW)‐corrected density functional theory (DFT) calculations and nudged elastic band (NEB) simulations.