MOF catches xenon and krypton

A porous metal-organic framework (MOF) material that sucks up record amounts of xenon and krypton could offer an energy-efficient way to capture those gases during nuclear waste processing (Angew. Chem., Int. Ed. 2022, DOI: 10.1002/anie.202117807). Traces of radioactive xenon and krypton contaminate oxygen, nitrogen, and other gases released during nuclear reprocessing. Expensive cryogenic distillation is typically used to remove these isotopes and ensure they don’t escape into the environment. Researchers now have found that a MOF identified 20 years ago (J. Am. Chem. Soc. 2000, DOI: 10.1021/ja003159k) can grab more xenon and krypton than other porous materials. The MOF is a lattice of copper ions connected by adamantane tetracarboxylate ligands. Its pores are lined with C–H groups that preferentially bind the two noble gases, and some of them can shrink to fit perfectly around the gas atoms, says team member Shengqian Ma of the University of North Texas. The researchers tested the MOF with a mixture of oxygen and nitrogen containing 400 ppm xenon and 40 ppm krypton, a composition typical of the gas released during nuclear reprocessing. At atmospheric pressure and 25 °C, the MOF’s capacity for xenon was 32 mmol/kg of material, almost three times as much as the previous record holder, and its krypton capacity reached a new high of 8 mmol/kg. “In terms of the overall performance, it could replace cryogenic methods,” Ma says. The team is now trying to reduce the cost of the ligand and produce the MOF at kilogram scale, potentially using a flow reactor.