Capturing the Elusive: A Snapshot of the Pu(IV) Hexanuclear Cluster Intermediate in the Birth of PuO₂ Colloidal...

While recent studies have provided a wealth of information about the structure of oxide nanoparticles resulting from Pu(IV) hydrolysis, little is known about their formation mechanism. This article describes the stabilization and characterization of a reaction intermediate observed during the formation of PuO₂ colloidal nanoparticles in aqueous solution. The intermediate was captured by a kinetic blocking of the started hydrolysis reaction by dilution of the reacting medium into DOTA (pH 3.5), glycine (pH 2.0), or acetic acid (pH 1.1) aqueous solutions. Such an approach stopped the hydrolysis and condensation processes by complexation and allowed for stabilization of hexameric polynuclear structures of Pu(IV) that were thoroughly characterized using laboratory and synchrotron techniques (UV-vis, small angle X-ray scattering, L₃-edge X-ray absorption spectroscopy, and M₄-edge high energy resolution fluorescence detected-X-ray absorption near edge structure). Beyond the new insight given about the contribution of the [Pu₆O₄(OH)₄]¹²⁺ cluster during the aqueous formation of colloidal PuO₂ nanoparticles in aqueous conditions, this study confirms the added value of synchrotron radiation for the characterization of very dilute and strongly radioactive nanostructures, paving the way for further research in the domain.