X-ray absorption experiments at Ce L₃ and M₅ edges and theoretical calculations demonstrate that in addition to the nanoceria charge stability, the formation of hydroxyl groups at the surface affects the chemical performance of nanomaterials.

Oh, now I see! The precipitates formed during Th^IV hydrolysis are ThO₂ nanoparticles, which in their initial stages of formation are a mixture of ultra‐small nanoparticles and Th hexamer clusters. This new structural insight is made possible by the combined use of two synchrotron techniques: HEXS and XANES in HERFD mode, which probe short‐ and medium‐range order in the sample under study. More information can be found in the Full Paper by L. Amidani et al. (DOI: 10.1002/chem.202003360).

Here we provide evidence that the formation of PuO₂ nanoparticles from oxidized Pu^VI under alkaline conditions proceeds through the formation of an intermediate Pu^V solid phase, similar to NH₄PuO₂CO₃, which is stable over a period of several months. For the first time, state‐of‐the‐art experiments at Pu M₄ and at L₃ absorption edges combined with theoretical calculations unambiguously allow to determine the oxidation state and the local structure of this intermediate phase.

We report a full characterization of PuO₂nanoparticles at the atomic level and probe their local and electronic structure by a variety of methods available at the synchrotron and theoretical approaches.

High-resolution XANES spectra of small ThO ₂ nanoparticles show the signature of the more exposed Th atoms at the surface.

The structural characterisation of actinide nanoparticles (NPs) is of primary importance and hard to achieve, especially for non‐homogeneous samples with NPs less than 3 nm. By combining high‐energy X‐ray scattering (HEXS) and high‐energy‐resolution fluorescence‐detected X‐ray absorption near‐edge structure (HERFD XANES) analysis, we have characterised for the first time both the short‐ and medium‐range order of ThO₂ NPs obtained by chemical precipitation. By using this methodology, a novel insight into the structures of NPs at different stages of their formation has been achieved. The pair distribution function revealed a high concentration of ThO₂ small units similar to thorium hexamer clusters mixed with 1 nm ThO₂ NPs in the initial steps of formation. Drying the precipitates at around 150 °C promoted the recrystallisation of the smallest units into more thermodynamically stable ThO₂ NPs. HERFD XANES analysis at the thorium M₄ edge, a direct probe for f states, showed variations that we have correlated with the breakdown of the local symmetry around the thorium atoms, which most likely concerns surface atoms. Together, HEXS and HERFD XANES are a powerful methodology for investigating actinide NPs and their formation mechanism.