Uranium oxide at the nanoscale is relevant towards understanding the impact of decreasing grain size in advanced nuclear fuels and to understand UO<sub>2</sub> corrosion and mobility within environmental systems. Additionally, nanoparticulate actinide oxides provide a means to explore the surface and interface characteristics of these materials, due to their high percentage of surface atoms, which makes spectroscopic methods sensitive to their surface chemistry. Investigations into uranium oxide nanoscale and surface properties, however, require: 1) empirically well-developed methods to synthesize actinide oxide nanoparticles with controlled size and crystallographic phase and 2) characterization capabilities to explore the atomic and nanoscale structure of actinide oxide particles in detail to make connections between structure/property relationships. Our efforts involve a combination of synthetic pursuits and the development of new X-ray data analysis tools to optimize X-ray absorption and scattering-based techniques for use with actinide oxide particles on the nanoscale. This multi-faceted approach enables a feedback loop through which characterization developments can better inform synthetic strategies.<br/><br/>Uranium oxide nanoparticles in the size range from 2 – 100 nm are controlled using colloidal and hard template-based approaches. Through characterizing particles with a wide range of sizes, the surface area to volume ratio can be tuned. Ultrasmall nanoparticles (&lt; 3 nm) are particularly useful, given that a majority of atoms reside on the particle surface making conventionally bulk characterization techniques such as X-ray absorption spectroscopy (XAFS) surface-sensitive probes. New models will be presented that provide an indication of elemental speciation of surface atoms and sites for surface ligand binding, through combining geometric models with structural parameters extracted from XAFS. Additionally, the development of X-ray scattering (SAXS/WAXS) software to characterize samples with complex containment backgrounds will be discussed. Results obtained through this work are broadly applicable towards resolving nanoparticle surface chemistry and provide foundational methodology for the characterization of actinide oxides, and the ability to resolve their emergent nanoscale properties.

Interrogating the surface chemistry of nanoscale uranium oxides

ACS Spring 2022

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