Uniform formation of uranium oxide nanocrystals inside ordered mesoporous hosts and their potential applications as oxidative catalysts

Structural properties of ultra-small thorium and uranium dioxide nanoparticles embedded in a covalent organic framework

We report the structural properties of ultra-small ThO2 and UO2 nanoparticles (NPs), which were synthesized without strong binding surface ligands by employing a covalent organic framework (COF-5) as an inert template. The resultant NPs were used to observe how structural properties are affected by decreasing grain size within bulk actinide oxides, which has implications for understanding the behavior of nuclear fuel materials. Through a comprehensive characterization strategy, we gain insight regarding how structure at the NP surface differs from the interior. Characterization using electron microscopy and small-angle X-ray scattering indicates that growth of the ThO2 and UO2 NPs was confined by the pores of the COF template, resulting in sub-3 nm particles. X-ray absorption fine structure spectroscopy results indicate that the NPs are best described as ThO2 and UO2 materials with unpassivated surfaces. The surface layers of these particles compensate for high surface energy by exhibiting a broader distribution of Th-O and U-O bond distances despite retaining average bond lengths that are characteristic of bulk ThO2 and UO2. The combined synthesis and physical characterization efforts provide a detailed picture of actinide oxide structure at the nanoscale, which remains highly underexplored compared to transition metal counterparts.

Mixed uranyl and neptunyl cation–cation interaction-driven clusters: structures, energetic stability, and nuclear quadrupole interactions

We present a quantum-chemical study of mixed CCI clusters, their structures, energetic stability, and nuclear quadrupole interactions.

Control of the compositions and morphologies of uranium oxide nanocrystals in the solution phase: multi-monomer growth and self-catalysis

The presence of mixed products and impurities, which always confuse researchers, are common during synthesizing nanomaterials. Even though many studies have been conducted with an objective to control the synthesis of nanomaterials, very few studies have investigated a mechanism to control the composition of nanomaterials. Various products include UO₃·H₂O, U₃O₈, UO₂, and U₄O₉ were produced by simply adjusting the pH with ammonia. The morphology of UO₂ and U₃O₈ are tunable. In this study, we suggest two mechanisms that can be used to control the nanomaterial composition. Various experiments have been conducted to understand the mechanism that controls the composition of nanomaterials. We indicate that a multi-monomer growth model can be used to control the uranium oxide composition. We have developed a new oxidation-reduction system using acetone, and this system is capable of controlling both the morphology and composition of uranium oxide micro/nanomaterials. Further, the presence of the self-catalysis mechanism can be used to regulate processes that control the monomer transformation. Thus, the results of this study can be applied to help in the construction of mixed-valence metal oxides.

Radiolytic syntheses of hollow UO2 nanospheres in Triton X-100-based lyotropic liquid crystals

Hollow nanospheres (ϕ: 60–80 nm, wall thickness: 10–20 nm), consisted of UO2 nanoparticles (ϕ: 3–5 nm), were successfully prepared in a Triton X-100-water (50:50, w/w) hexagonal lyotropic liquid crystal (LLC) by γ-irradiation, where water soluble ammonium uranyl tricarbonate was added as precursor. The product was stable at least up to 300°C. Furthermore, whether the nanospheres were hollow or not, and the wall thickness of the hollow nanospheres could be easily controlled via adjusting dose rate. While in the Triton X-100 based micellar systems, only solid nanospheres were obtained. At last, a possible combination mechanism containing adsorption, aggregation and fracturing processes was proposed.

Ultra-small plutonium oxide nanocrystals: an innovative material in plutonium science

Apart from its technological importance, plutonium (Pu) is also one of the most intriguing elements because of its non-conventional physical properties and fascinating chemistry. Those fundamental aspects are particularly interesting when dealing with the challenging study of plutonium-based nanomaterials. Here we show that ultra-small (3.2±0.9 nm) and highly crystalline plutonium oxide (PuO2 ) nanocrystals (NCs) can be synthesized by the thermal decomposition of plutonyl nitrate ([PuO2 (NO3 )2 ]⋅3 H2 O) in a highly coordinating organic medium. This is the first example reporting on the preparation of significant quantities (several tens of milligrams) of PuO2 NCs, in a controllable and reproducible manner. The structure and magnetic properties of PuO2 NCs have been characterized by a wide variety of techniques (powder X-ray diffraction (PXRD), X-ray absorption fine structure (XAFS), X-ray absorption near edge structure (XANES), TEM, IR, Raman, UV/Vis spectroscopies, and superconducting quantum interference device (SQUID) magnetometry). The current PuO2 NCs constitute an innovative material for the study of challenging problems as diverse as the transport behavior of plutonium in the environment or size and shape effects on the physics of transuranium elements.

Synthesis of Colloidal Uranium−Dioxide Nanocrystals

In this paper, we have developed an organic-phase synthesis method for producing size-controlled, nearly monodispersed, colloidal uranium-dioxide nanocrystals. These UO2 nanocrystals are potentially important to applications such as nuclear fuel materials, catalysts, and thermopower materials. In addition, we have systematically mapped out the functions of the solvents (oleic acid, oleylamine, and 1-octadecene) in the synthesis, and we found that N-(cis-9-octadecenyl)oleamide-a product of the condensation of oleic acid and oleylamine-can substantially affect the formation of UO2 nanocrystals. Importantly, these results provide fundamental insight into the mechanisms of UO2 nanocrystal synthesis. Moreover, because a mixture of oleic acid and oleylamine has been widely used in synthesizing a variety of high-quality metal or metal-oxide nanocrystals, the results herein should also be important for understanding the detailed mechanisms of these syntheses.