Synthesis and characterization of thorium, uranium and cerium oxide nanoparticles

Abstract

We describe the synthesis of cerium, thorium and uranium oxide nanoparticles embedded in a mesoporous matrix as template in a kind of nanocasting technique. The solid matrix is used as a template to obtain and stabilize the actinide oxide nanoparticles. We apply high resolution transmission electron microscopy (HR-TEM) to show evidence of metal oxide incorporation into the matrix pores and analyze their structure. Measured interplanar distances and calculated lattice parameters for synthesized nanosized CeO_2−x and ThO₂ samples differ from their bulk crystalline counterparts. We obtain with our synthesis CeO_2−x particles containing both Ce⁴⁺ and larger sized Ce³⁺. The lattice parameter for these ceria nanoparticles is found to be larger than the bulk value due to the presence of Ce³⁺ with its larger ionic radius. The presence of Ce³⁺ was established by means of high resolution X-ray emission spectroscopy (HRXES), applied to the investigation of nanoparticles for the first time. The ThO₂ nanoparticles exhibit a decrease in interplanar distances, as one might generally expected for these nanoclusters. However, the lattice distance decrease for our particles is remarkable, up to 5%, indicating that contact with the surrounding silica matrix may exert a bond distance shortening effect such as through significant external pressure on the particle surface.