Abstract
While bulk PuO₂ is known to be highly refractory to dissolution, even under ultrasonic irradiation, this study demonstrates that nanometric PuO₂ samples can exhibit unique reactivity when sonicated under an Ar/(20%)O₂ atmosphere. Interestingly, this reactivity does not appear to be related to nanoparticle size but rather to the preparation method and possibly to the nanoparticle surface state. 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 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 suggesting an important role of the 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 could generate similar chemical environments.