Polyoxometalates (POMs) are metal oxide clusters truncated by doubly- or triply-bonded O atoms. Whereas transition-metal POMs have been extensively studied, uranyl-based POMs, also known as uranyl peroxide nanoclusters, have been known for approximately a decade. In contrast to most transition-metal POMs, the uranyl peroxide nanoclusters can form cages that encapsulate cations. They are stable in aqueous solution and their very large surface-to-volume ratios ensure that liquid-“solid” interfaces can be probed at the nanoscale. This work describes the nanoscale interactions of the uranyl peroxide nanoclusters LiNa-U24 (Li23Na[UO2O2OH]24*58H2O) and U24Pp12 (Li24Na24[(UO2O2)24(P2O7)12]) with plutonium(VI) and neptunium(V). Ultra-small angle X-ray scattering (USAXS), small angle X-ray scattering (SAXS), and dynamic light scattering (DLS) were used to describe the aggregation of individual nanoclusters into secondary and tertiary structures in solution, whereas UV-vis-NIR spectroscopy was used to monitor for redox changes. Understanding redox chemistry and aggregation is essential for the consideration of actinide separation schemes via size filtration, which could potentially lead to new approaches to the reprocessing of used nuclear fuel.

Nanoscale interactions of neptunium and plutonium with uranyl peroxide nanoclusters

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