Unveiling the dual reactivity of nanoscaled PuO sonicated in oxygenated aqueous solutions.

While bulk PuO is known to be strongly resistant to dissolution, even under ultrasonic irradiation, this study demonstrates that nanometric PuO samples can exhibit enhanced reactivity when sonicated under an Ar/(20 %)O atmosphere. Sonication of powdered PuO nanoparticles (∼5 nm) in pure water was found to be ineffective. In contrast, colloidal PuO nanoparticles (∼3 nm) prepared via hydrolysis exhibited markedly different behavior, leading to the accumulation of Pu(VI), with sonochemically-generated HO 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 PuO nanoparticles, this study highlights their dual reactivity under conditions favoring HO formation highlighting an important role of the material's preparation method. Beyond underscoring the critical role of HO in the reactivity of PuO nanoparticles, this study also evidences a potential pathway for their transformation under environmental conditions where radiolysis can generate similar chemical environments.