Sol-Gel Synthesis of High-Purity Actinide Oxide ThO2 and Its Solid Solutions with Technologically Important Tin and Zinc Ions

The applicability of epoxide-based sol gel synthesis for actinide oxide (thoria) starting from air-stable salt, Th(NO3)(4), has been examined. The homogeneous gel formed from Th(NO3)(4) when calcined at 400 degrees C yielded nanostructured thoria, and with increasing tempeartures (600, 700, and 800 degrees C), the average crystallite size increased. Successful Rietveld refinement of the powder X-ray diffraction pattern of ThO2 in Fm (3) over barm space group was carried out with a = 5.6030(35) angstrom. The fingerprint vibrational mode of the fluorite structure of ThO2 was noticed as a sharp band in the Raman spectrum at 457 car(-1). In the SEM image, a near spherical morphology of thoria was noticed. Samples showed blue emission on exciting with lambda = 380 nm in the photoluminescence spectrum indicative of the presence of defects. Following this approach, 50 mol % of Sn4+ could be substituted for Th4+, retaining the fluorite structure as evidenced by the PXRD, Raman spectroscopy, electron microscopy, EDAX, and XPS measurements. Randomization of the lattice was observed for the tin-substituted samples. A significant blue shift in the absorption threshold along with a persistent blue emission in the photoluminesence spectra were evident for the tin-substituted samples. The concentration of Zn2+ ion in thoria was limited to 15 mol % as revealed by PXRD and XPS measurements. The Raman peak shifted to higher values for Zn2+-substituted samples. A change in the optical absorbance characteristics was observed for the zinc-substituted thoria. A 50 mol % Sn4+-substituted thoria degraded aqueous Rhodamine 6G dye solutions in the presence of UV vis radiation following pseudo-first-order kinetics.