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

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.