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An ultrastable uranyl arylphosphonate framework as depleted uranium waste form with abundant coordinated water features marked entrapment of trivalent f-block elements (i.e., Eu3+, Am3+) from aqueous solutions as well as moderate uptake of toxic SO 2 and NH 3. The coordinated water can not only bind guest species together with phosphonate groups but also participate in the unprecedented Eu3+ → UO 2 2+ transmetalation. [Display omitted] • A highly robust uranyl phosphonate framework was fabricated. • UPF-205 features marked entrapment of Eu3+, Am3+ from aqueous solutions. • A hitherto unknown transmetalation between Eu3+ and UO 2 2+ was discovered. • The coordinated water binds guest species together with phosphonate groups. • The uptake of SO 2 significantly increased upon removing the coordinated water. The design and fabrication of uranium phosphonate frameworks (UPFs) pave a potential avenue to reduce the environmental risk of depleted uranium, transuranium waste, and toxic gases while adding to its waste to utility virtues. However, it remains unknown how the pervasive coordinated water of UPFs influences their performances in radionuclide and toxic gas separation. Toward this end, we prepared a new category of porous UPFs, namely UPF-205 with abundant coordinated water and resulting hydrogen bonding nanotraps. The coordinated water is synergistic in quantitatively removing trivalent f-elements (i.e., Am3+, Eu3+) from wide-ranging pH solutions together with proximal phosphonate groups at a low metal concentration. Most importantly, an unprecedented coordinated water-mediated Eu3+-UO 2 2+ transmetalation had been verified at a relatively high metal concentration. The high-density open uranyl sites and optimal pore size triggered by the dehydration of coordinated water also contribute to the enhanced adsorption of toxic SO 2 and NH 3. Our work shows great relevance for the rational design of ultrastable UPFs as both depleted uranium waste forms and efficient adsorbents for radiological/nuclear protection. [ABSTRACT FROM AUTHOR]

The mysterious properties of individual U atoms on transition metal surfaces play indispensable parts in supplementing our understanding of uranium-transition metal systems, which are important subjects for both nuclear energy applications and fundamental scientific studies. By using scanning tunneling microscopy and density functional theory calculations, the adsorptions, reactions and electronic properties of individual U atoms on Cu(111), Ag(111), Au(111) and Ru(0001) surfaces were comparatively studied for the first time in this work. Upon the deposition of a small amount of U onto Cu(111) or Ag(111) at 8 K, individual U atoms show relatively high activity and can either be adsorbed on intact substrate surfaces or induce various surface vacancies surrounded by clusters of substrate atoms. By contrast, the majority of U atoms tend to dispersedly adsorb on intact surfaces of Au(111) and Ru(0001) rather than producing surface vacancies at the same temperature. In all cases, Kondo resonance manifested as asymmetric dip feature around Fermi energy is only observed in the differential tunneling conductance spectra of single U adatoms on Ag(111). [ABSTRACT FROM AUTHOR]

The hydrogenation of metallic plutonium (Pu) is a crucial issue for its actual applications. In-depth scientific understanding of the hydriding corrosion process of Pu requires established values of rates and associated microscopic mechanism of hydrogen diffusion in the reaction product plutonium hydrides. Therefore, in this work we investigate the hydrogen diffusion in the stoichiometric plutonium dihydride and the non-stoichiometric one that contains tetrahedral hydrogen vacancies from first principles. Our results reveal the microscopic dynamical behavior of hydrogen in these compounds and indicate that the dominant diffusion mechanism greatly depends on the temperature and composition. [ABSTRACT FROM AUTHOR]

Oxidation state (OS) is one of the most important concepts in chemistry and, the challenging task is how to rigorously determine the OS of multivalent solid ions of which uranium is the outstanding example. Herein, we revisit the OS of solid uranium ions in a rich variety of compounds by calculating density functional theory (DFT)-based OS (OS DFT). The results disclose the variations of uranium OS DFT with chemical surrounding and local structure; OS DFT is generally consistent with formal OS (OS f) in the ionic approximation for the majority of compounds. Interestingly, uranium OS DFT in some compounds containing uranyl or uranyl-like units, e.g., β-/γ-UO 3 , and UO 2 X 2 (X = F, Cl, Br, OH), adopt U4+, instead of the textbook and never contradicted U6+ for gaseous and liquid uranyl ions. The associative effects from ligand-ligand interaction, steric repulsion, crystal-field splitting and delocalization-localization dual nature of 5f electrons are proposed to be responsible for the unusual OS behavior in solid-state uranium compounds. [ABSTRACT FROM AUTHOR]