Insight into the structure-property relation of UO2 nanoparticles

TL;DR

This study synthesizes and characterizes ultra-small UO2 nanoparticles, revealing their oxidation behavior, growth dynamics, and comparison with other actinide and lanthanide oxide nanoparticles.

Contribution

It provides detailed structural and spectroscopic analysis of UO2 nanoparticles, highlighting their oxidation process and size evolution, which was not previously well understood.

Findings

UO2 NPs oxidize to U4O9 over time and under X-ray exposure

UO2 NPs grow from 2-3 nm to 6 nm during oxidation

Distinct properties of UO2 NPs compared to PuO2, ThO2, and CeO2 NPs

Abstract

Highly crystalline UO2 nanoparticles (NPs) with sizes of 2-3 nm were produced by fast chemical deposition of uranium(IV) under reducing conditions at pH 8-11. The particles were then characterized by microscopic and spectroscopic techniques including high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), high-energy resolution fluorescence detection (HERFD) X-ray absorption spectroscopy at the U M4 edge and extended X-ray absorption fine structure (EXAFS) spectroscopy at the U L3 edge. The results of this investigation show that despite U(IV) being the dominant oxidation state of the freshly prepared UO2 NPs, they oxidize to U4O9 with time and under the X-ray beam, indicating the high reactivity of U(IV) under these conditions. Moreover, it was found that the oxidation process of NPs is accompanied by their growth in size to 6 nm. We highlight here the major differences and similarities of the UO2 NPs properties with PuO2, ThO2 and CeO2 NPs.