Researchers from Northwestern University and Argonne National Lab have developed a material that can grab and encapsulate radioactive cesium isotopes, much like a Venus Flytrap does with flies. Cesium is an abundant byproduct of nuclear waste and has been difficult to concentrate/separate when cleaning up superfund sites polluted with the substance.
The new material, a rigid frame composed of metal sulfides, has a negative charge. Its pores, therefore, attract positively charged ions. This makes it a good candidate for ion exchange—when immersed in a solution with other positive ions, the ions tucked inside the pores switch places with the ions outside.
Sodium ions do this dance freely, switching as many times as they’re immersed. However, when the team filled the material with cesium ions, they refused to move out of the material.
To find out why the material trapped cesium but not sodium, Kanatzidis [Mercouri Kanatzidis, Argonne] and Ding [Nan Ding, Northwestern] had to come up with an image of the material’s crystalline structure itself. They found that sodium bonded strongly to the water in the solution, which prevented it from becoming trapped by the framework; but a cesium ion doesn’t form strong bonds with water molecules, so it has less protection. The ion binds to several sulfur atoms in the rings of the framework, causing the rings to change shape, and the hole is sealed shut.
Press release: New material traps radioactive ions using “Venus flytrap” method …
Abstract in Nature Chemistry: Selective incarceration of caesium ions by Venus flytrap action of a flexible framework sulfide
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