# Unveiling the dual reactivity of nanoscaled PuO2 sonicated in oxygenated aqueous solutions

## TL;DR

Tiny PuO2 particles react differently when exposed to sound waves in oxygen-rich water, producing a reactive form of plutonium.

## Contribution

Shows that preparation method affects PuO2 nanoparticle reactivity via hydrogen peroxide generation during sonication.

## Key findings

- Nanoscale PuO2 particles prepared by hydrolysis produce Pu(VI) during sonication in oxygenated water.
- Hydrogen peroxide generated by sonication is crucial for PuO2 nanoparticle reactivity.
- A Pu(IV) peroxide intermediate was identified in the dissolution process.

## Abstract

While bulk PuO2 is known to be strongly resistant to dissolution, even under ultrasonic irradiation, this study demonstrates that nanometric PuO2 samples can exhibit enhanced reactivity when sonicated under an Ar/(20 %)O2 atmosphere. Sonication of powdered PuO2 nanoparticles (∼5 nm) in pure water was found to be ineffective. In contrast, colloidal PuO2 nanoparticles (∼3 nm) prepared via hydrolysis exhibited markedly different behavior, leading to the accumulation of Pu(VI), with sonochemically-generated H2O2 playing a crucial role in the process. Further investigations identified an intermediate species implicated in the dissolution process, agreeing with a recently described Pu(IV) peroxide compound. Despite the chemical similarity of the PuO2 nanoparticles, this study highlights their dual reactivity under conditions favoring H2O2 formation highlighting an important role of the material’s preparation method. Beyond underscoring the critical role of H2O2 in the reactivity of PuO2 nanoparticles, this study also evidences a potential pathway for their transformation under environmental conditions where radiolysis can generate similar chemical environments.