A material with an open framework that can selectively trap and hold onto a form of potentially dangerous nuclear waste, caesium ions, is described in Nature Chemistry this week. A radioactive isotope of caesium, caesium-137, is highly toxic and is believed to be the main source of radiation still present around Chernobyl.
Nan Ding and Mercouri Kanatzidis created a sulfide material that has a flexible structure containing organic cations that can swap places with caesium ions in an aqueous solution. This triggers the structure to change shape such that windows in the sulfide framework 'close' around the caesium ions, in a manner reminiscent of a Venus flytrap, so that they cannot escape. Other similar ions are not trapped by the material, even when present in much greater concentrations.
Caesium-137 can be produced by nuclear fission. It is water-soluble and highly toxic, and so poses a high risk if released into the environment, where it can persist for many years.