Computational study of radioactive cesium capture in copper hexacyanoferrate structures for nuclear waste applications*

Radioactive cesium is one of the most common and problematic products of nuclear fission and energy production. Currently, there is no permanent solution to rid nuclear waste of radioactive cesium. Copper hexacyanoferrate compounds, known as Prussian blue analogues (PBA), have shown early promise in capturing cesium cations through a sorption mechanism. Using the institutional cluster at Brookhaven National Laboratory (BNL), we utilize density functional theory calculations to characterize the structure of PBAs as well as its changes during the cesium exchange. Computational models allow us to refine structural details that may be difficult to explore experimentally. We investigate the PBA structure before and after cesium exchange to provide insights into the sorption mechanism to complement experimental studies using X-ray diffraction methods. Based on our results, we show that the lattice structure expands when the potassium is exchanged with cesium due to the larger ionic radius of cesium. Furthermore, the modeling studies support the structural assumption that cesium prefers to occupy the center of the cavity, the Wyckoff 8c site.