Nanoscale uranyl peroxide cage clusters are self-assembled structures with uranyl polyhedra linked through peroxide bridges. Charge-balancing alkali ions are located both inside and outside of these negatively charged nanoscale capsules. While the peroxide bridges between uranyl polyhedra are necessary in order to give them a bent structure, introduction of other functional groups such as oxalate, pyrophosphate and hydroxyl can lead to the presence of oxalate, pyrophosphate, phosphite, and two hydroxyl group bridges between actinyl ions as well. Due to their physical and chemical properties, uranyl peroxide clusters have potential applications in the nuclear industry and nuclear fuel cycle such as in uranium mining, purification, separations, and storage of spent nuclear fuel. Yet, their thermodynamic properties that govern their formation and stability in different environments are poorly studied, except for U60 and U28 with 60 and 28 uranyl polyhedra, respectively. In this study, the enthalpy of formation of four uranyl clusters with different ligands and different numbers of uranyl polyhedra as well as charge balancing alkali ions were calculated from the enthalpy of dissolution in a high-temperature oxide melt solution calorimeter. U28PO<sub>3</sub> with phosphite bridges, Li/k and K/Na salts of U24P with pyrophosphate bridges, and U32 with hydroxyl bridges were the subject of this study. The role of the number of alkali ions, different types of ligands, and number of uranium atoms or peroxide groups per cluster in determining the stability of these clusters has been studied separately to identify the dominant factors in the stability of these nano complexes.

Energetic studies of different uranyl nanoclusters

251st National Meeting (2016)

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