Stable Uranium Research Articles

π-electron injection activated dormant ligands in graphitic carbon nitride for efficient and stable uranium extraction

Graphitic carbon nitride (CN) as an adsorbent exhibit promising potential for the removal of uranium in water. However, the lack of active sites seriously restricts its practical application. In contrast to the traditional method of introducing new ligands, we propose a strategy to activate original ligands on CN by injecting π electrons, which can be realized by grafting 4-phenoxyphenol (PP) on CN (PCN). Compared with CN, the maximum adsorption capacity of PCN for uranium increased from 150.9 mg/g to 380.6 mg/g. Furthermore, PCN maintains good adsorption properties over a wide range of uranium concentrations (1 ∼ 60 mg/L) and pH (4 ∼ 8). After 5 consecutive cycles, PCN exhibited sustained uranium removal performance with a little of losses. The experimental and theoretical results show that the enhancement of adsorption performance is mainly due to the ligands activation of CN by delocalization of π electrons from PP. Furthermore, this activation can be enhanced by irradiation, as the CN can be photoexcited to provide additional photoelectrons for PP. As a result, dormant ligands such as N-CN, C-O-C, C-N-H and N-(C)3 can be activated to participate in coordination with uranium. This work provides theoretical guidance for the design and preparation of high efficiency uranium adsorbent.

Ambient melting behavior of stoichiometric uranium oxides

As UO2 is easily oxidized during the nuclear fuel cycle it is important to have a detailed understanding of the structures and properties of the oxidation products. Experimental work over the years has revealed many stable uranium oxides including UO2, U4O9 (UO2.25), U3O7 (UO2.33), U2O5 (UO2.5), U3O8 (UO2.67), and UO3, all with a number of different polymorphs. These oxides are broadly split into two categories, fluorite-based structures with stoichiometries in the range of UO2 to UO2.5 and less dense layered-type structures with stoichiometries in the range of UO2.5 to UO3. While UO2 is well characterized, both experimentally and computationally, there is a paucity of data concerning higher stoichiometry oxides in the literature. In this work we determine the ambient melting points of all the six stoichiometric uranium oxides listed above and compare them to the available experimental and/or theoretical data. We demonstrate that a family of the six ambient melting points map out a solid-liquid transition boundary consistent with the high-temperature portion of the phase diagram of uranium-oxygen system suggested by Babelot et al.

A multiclass classification model for predicting the thermal conductivity of uranium compounds

ABSTRACT Advanced nuclear fuels are designed to offer improved performance and accident tolerance, with an emphasis on achieving higher thermal conductivity. While promising fuel candidates like uranium nitrides, carbides, and silicides have been widely studied, the majority of uranium compounds remain unexplored. To search for potential candidates among these unexplored uranium compounds, we incorporated machine learning to accelerate the material discovery process. In this study, we trained a multiclass classification model to predict a compound’s thermal conductivity based on 133 input features derived from element properties and temperature. The initial training data consist of over 160,000 processed thermal conductivity records from the Starrydata2 database, but a skewed data class distribution led the trained model to underestimate compound’s thermal conductivity. Consequently, we addressed the issue of class imbalance by applying Synthetic Minority Oversampling TEchnique and Random UnderSampling, improving the recall for materials with thermal conductivity higher than 15 W/mK from 0.64 to 0.71. Finally, our best model is used to identify 119 potential advanced fuel candidates with high thermal conductivity among 774 stable uranium compounds. Our results underscore the potential of machine learning in the field of nuclear science, accelerating the discovery of advanced nuclear materials.

Stable Uranium Oxide Under Atmospheric Conditions: An Electroplating Technique for U Film Fabrication at Boron-Doped Diamond Electrodes

Stable Uranium Oxide Under Atmospheric Conditions: An Electroplating Technique for U Film Fabrication at Boron-Doped Diamond Electrodes

Uranium-Mediated Peroxide Activation and a Precursor toward an Elusive Uranium cis-Dioxo Fleeting Intermediate.

The activation of chalcogen-chalcogen bonds using organometallic uranium complexes has been well documented for S-S, Se-Se, and Te-Te bonds. In stark contrast, reports concerning the ability of a uranium complex to activate the O-O bond of an organic peroxide are exceedingly rare. Herein, we describe the peroxide O-O bond cleavage of 9,10-diphenylanthracene-9,10-endoperoxide in nonaqueous media, mediated by a uranium(III) precursor [((Me,AdArO)3N)UIII(dme)] to generate a stable uranium(V) bis-alkoxide complex, namely, [((Me,AdArO)3N)UV(DPAP)]. This reaction proceeds via an isolable, alkoxide-bridged diuranium(IV/IV) species, implying that the oxidative addition occurs in two sequential, single-electron oxidations of the metal center, including rebound of a terminal oxygen radical. This uranium(V) bis-alkoxide can then be reduced with KC8 to form a uranium(IV) complex, which upon exposure to UV light, in solution, releases 9,10-diphenylanthracene to generate a cyclic uranyl trimer through formal two-electron photooxidation. Analysis of the mechanism of this photochemical oxidation via density functional theory (DFT) calculations indicates that the formation of this uranyl trimer occurs through a fleeting uranium cis-dioxo intermediate. At room temperature, this cis-configured dioxo species rapidly isomerizes to a more stable trans configuration through the release of one of the alkoxide ligands from the complex, which then goes on to form the isolated uranyl trimer complex.

Interface-Constrained Layered Double Hydroxides for Stable Uranium Capture in Highly Acidic Industrial Wastewater.

Low acid endurance of layered double hydroxides (LDHs) limits their uranium(VI) [U(VI)] adsorption capability from harsh industrial wastewater. Here, we demonstrate magnesium-cobalt LDHs (Mg-Co LDHs) anchored in situ onto the pore channel of dendritic fibrous nanosilica (DFNS) via an interface-constrained strategy. The synergy of Mg-Co LDHs and DFNS not only improves the endurance of the Mg-Co LDH under harsh acidic conditions but also increases the number of active sites of DFNS. Thus, DFNS@Mg-Co LDH shows a high U(VI) uptake capacity (1143 mg g-1) at pH = 3 and C0 = 598.7 mg L-1, which is about 4.8-fold higher than that of pristine DFNS. The DFNS@Mg-Co LDH exhibits excellent U(VI) uptake in various background water circumstances due to its acid endurance and highly selective adsorption. This interface-constrained strategy provides LDH materials with durability under extremely acidic conditions along with a high adsorption capacity, which is promising for uranium capture from various water fields.

Uranium versus Thorium: Synthesis and Reactivity of [η5 -1,2,4-(Me3 C)3 C5 H2 ]2 U[η2 -C2 Ph2

The synthesis, electronic structure, and reactivity of a uranium metallacyclopropene were comprehensively studied. Addition of diphenylacetylene (PhC≡CPh) to the uranium phosphinidene metallocene [η 5‐1,2,4‐(Me3C)3C5H2]2U=P‐2,4,6‐tBu3C6H2 (1) yields the stable uranium metallacyclopropene, [η 5‐1,2,4‐(Me3C)3C5H2]2U[η 2‐C2Ph2] (2). Based on density functional theory (DFT) results the 5f orbital contributions to the bonding within the metallacyclopropene U‐(η 2‐C=C) moiety increases significantly compared to the related ThIV compound [η 5‐1,2,4‐(Me3C)3C5H2]2Th[η 2‐C2Ph2], which also results in more covalent bonds between the [η 5‐1,2,4‐(Me3C)3C5H2]2U2+ and [η 2‐C2Ph2]2− fragments. Although the thorium and uranium complexes are structurally closely related, different reaction patterns are therefore observed. For example, 2 reacts as a masked synthon for the low‐valent uranium(II) metallocene [η 5‐1,2,4‐(Me3C)3C5H2]2UII when reacted with Ph2E2 (E=S, Se), alkynes and a variety of hetero‐unsaturated molecules such as imines, ketazine, bipy, nitriles, organic azides, and azo derivatives. In contrast, five‐membered metallaheterocycles are accessible when 2 is treated with isothiocyanate, aldehydes, and ketones.

Alkynyl-Based sp 2 Carbon-Conjugated Covalent Organic Frameworks with Enhanced Uranium Extraction from Seawater by Photoinduced Multiple Effects

Biofouling is a major obstacle to the efficient extraction of uranium from seawater due to the numerous marine microorganisms in the ocean. Herein, we report a novel amidoxime (AO) crystalline cova...

Use of Potentiometric Titration for the Study of Thermodynamic Properties of UCl <sub>4</sub> and UO <sub>2</sub> in Fused LiCl-KCl Eutectic

The interaction between uranium oxygen-free and oxygen ions in molten LiCl-KCl eutectic (LKE) at 773 K was studied to investigate the chemical and electrochemical properties of U 4+ and O 2- ions by potentiometric titration method. Combining theoretical and experimental data, the E - p O 2- Pourbaix diagram for stable uranium compounds has been constructed. The stable states of U(IV) in molten LiCl-KCl salt at 773 K were UO 2 and UCl 4 during the concentration of oxygen ions reaches equivalent point α =2.39. The calculated values of the activity coefficient of UCl 4 and UCl 3 were 5.05×10 - 5 and 1.01×10 - 3 , respectively. This is indicated that U(III) ions are less active than U(IV) ions probably due to the formation of strong complexes with the chloride ions. Tungsten cathode was used to deposit metal uranium, and the equilibrium potentials vs. the Ag/AgCl reference electrode are -1.5005 V and -2.5305 V separately by using the emf of the galvanic cell. The potential of urnium ions in the melt was changed linearly with the concentration function of oxygen ions ( p O 2- ). According to the titration reaction, solid UO 2 was formed in the range 0 < α < 2.39. The equilibrium between UO 2 and U (IV) ions was described by the equation: E =3.678+0.0383´ p O 2- , by which the stability constant of UO 2 can be calculated. Meanwhile, the equilibrium of UO 2 with U(III) is as shown in the formula: E =2.107+0.154´ p O 2- .

Experimental Investigation of Uranium Volatility during Vapor Condensation.

The predictive models that describe the fate and transport of radioactive materials in the atmosphere following a nuclear incident (explosion or reactor accident) assume that uranium-bearing particulates would attain chemical equilibrium during vapor condensation. In this study, we show that kinetically driven processes in a system of rapidly decreasing temperature can result in substantial deviations from chemical equilibrium. This can cause uranium to condense out in oxidation states (e.g., UO3 vs UO2) that have different vapor pressures, significantly affecting uranium transport. To demonstrate this, we synthesized uranium oxide nanoparticles using a flow reactor under controlled conditions of temperature, pressure, and oxygen concentration. The atomized chemical reactants passing through an inductively coupled plasma cool from ∼5000 to 1000 K within milliseconds and form nanoparticles inside a flow reactor. The ex situ analysis of particulates by transmission electron microscopy revealed 2-10 nm crystallites of fcc-UO2 or α-UO3 depending on the amount of oxygen in the system. α-UO3 is the least thermodynamically preferred polymorph of UO3. The absence of stable uranium oxides with intermediate stoichiometries (e.g., U3O8) and sensitivity of the uranium oxidation states to local redox conditions highlight the importance of in situ measurements at high temperatures. Therefore, we developed a laser-based diagnostic to detect uranium oxide particles as they are formed inside the flow reactor. Our in situ measurements allowed us to quantify the changes in the number densities of the uranium oxide nanoparticles (e.g., UO3) as a function of oxygen gas concentration. Our results indicate that uranium can prefer to be in metastable crystal forms (i.e., α-UO3) that have higher vapor pressures than the refractory form (i.e., UO2) depending on the oxygen abundance in the surrounding environment. This demonstrates that the equilibrium processes may not dominate during rapid condensation processes, and thus kinetic models are required to fully describe uranium transport subsequent to nuclear incidents.

Study on Detection Method of Oxygen-Uranium Ratio of UO2-MO Pellets

In this paper, the determination method of the atomic ratio of oxygen to uranium in UO2-MO pellets was studied. Through the experiments of UO2-MO pellets with different composition ratios, the results showed that MO in UO2-MO pellets was a stable compound and did not participate in the thermogravimetric reaction. Only uranium dioxide was oxidized into stable uranium trioxide in oxygen. By accurately measuring the net weight of samples after dehydration and the total weight after oxidation, the formula for calculating the oxygen-uranium ratio of UO2-MO pellets is derived by formula derivation, and the RSD of this method is better than 0.13%.

Uranium polyhydrides at moderate pressures: Prediction, synthesis, and expected superconductivity.

Hydrogen-rich hydrides attract great attention due to recent theoretical (1) and then experimental discovery of record high-temperature superconductivity in H3S [T c = 203 K at 155 GPa (2)]. Here we search for stable uranium hydrides at pressures up to 500 GPa using ab initio evolutionary crystal structure prediction. Chemistry of the U-H system turned out to be extremely rich, with 14 new compounds, including hydrogen-rich UH5, UH6, U2H13, UH7, UH8, U2H17, and UH9. Their crystal structures are based on either common face-centered cubic or hexagonal close-packed uranium sublattice and unusual H8 cubic clusters. Our high-pressure experiments at 1 to 103 GPa confirm the predicted UH7, UH8, and three different phases of UH5, raising confidence about predictions of the other phases. Many of the newly predicted phases are expected to be high-temperature superconductors. The highest-T c superconductor is UH7, predicted to be thermodynamically stable at pressures above 22 GPa (with T c = 44 to 54 K), and this phase remains dynamically stable upon decompression to zero pressure (where it has T c = 57 to 66 K).

Crystal structure prediction of uranium hydrides at high pressure: A new hydrogen-rich phase

Uranium hydride is a novel hydrogen-rich system which contains 5f electrons. Uranium hydride can not only be used in the nuclear fuel industry, but also be a candidate of high superconducting-temperature materials. In this paper, we have searched the stable uranium hydride structures by using particle swarm optimization method and first-principles calculations. Besides UH8 and UH9, we find that UH17, which contains larger hydrogen content than most hydride materials reported before, is also stable at high pressure. The atomic structures, electronic structures and phase diagram of uranium hydrides are provided, and we find that all of the discovered uranium hydrides are metals with negligible magnetic moments.

Microbially Mediated Stable Uranium Phosphate Nano-Biominerals

Microbially Mediated Stable Uranium Phosphate Nano-Biominerals

Stable uranium sols as precursors for the elaboration of nanostructured nc-UO2 materials

This study presents a colloidal sol-gel and templating method to elaborate sols as precursors for nanostructured and nanocrystallized nc-UO2 materials. Several parameters were controlled in order to obtain such sols and materials, such as nanoparticles size, sol stability, target pore size and pores organization. In this study, the nanoparticles formation was managed controlling the thermodynamics of the surfactant solution and the U(IV) species polycondensation kinetics The kinetics of the nanoparticles formation has been limited by the availability of the uranium species either by their complexation either by their diffusion limitation. To reach this goal, two types of surfactant at a concentration allowing to obtain micelles were used: a carboxylate surfactant with a non-ionic ployethoxylated part able to complex multicharged ions (AKYPO® RO 90 VG), and alkyl polyglucosides (Glucopon® 215) in sufficient concentration allowing the decrease of the uranium species diffusion. The surfactant solutions, the sols elaborated by indirect precipitation from U(IV) solution, the sols after freeze-drying and the final materials were characterized by Small and Wide Angle X-ray Scattering, Infrared Spectroscopy and microscopy at various scale. The results show that the complexation by AKYPO and the good degradation of these molecules allowed to obtain stable sols and a promising partially nanostructured nc-UO2 materials. With Glucopon, its high concentration in the sol, led to a carbon enriched material with few nc-UO2 zones.

ChemInform Abstract: Evidence of Trivalent Am Substitution into U3O8.

AbstractIn view of aspects such as the leaching behavior of spent nuclear fuel stored in an oxidative environment as well as the potential intermixing of fission products (Pu and minor actinides) with U3O8 as the most stable uranium oxide, the latter is tested by fixing an aqueous solutions of UO22+ and Am3+ cations in a 90:10 atomic ratio at a weak‐acidic ion‐exchanger resin.

Influence of the 5f Orbitals on the Bonding and Reactivity in Organoactinides: Experimental and Computational Studies on a Uranium Metallacyclopropene.

The synthesis, structure, and reactivity of a uranium metallacyclopropene were comprehensively studied. Reduction of (η(5)-C5Me5)2UCl2 (1) with potassium graphite (KC8) in the presence of bis(trimethylsilyl)acetylene (Me3SiC≡CSiMe3) allows the first stable uranium metallacyclopropene (η(5)-C5Me5)2U[η(2)-C2(SiMe3)2] (2) to be isolated. Magnetic susceptibility data confirm that 2 is a U(IV) complex, and density functional theory (DFT) studies indicate substantial 5f orbital contributions to the bonding of the metallacyclopropene U-(η(2)-C═C) moiety, leading to more covalent bonds between the (η(5)-C5Me5)2U(2+) and [η(2)-C2(SiMe3)2](2-) fragments than those in the related Th(IV) compound. Consequently, very different reactivity patterns emerge, e.g., 2 can act as a source for the (η(5)-C5Me5)2U(II) fragment when reacted with alkynes and a variety of heterounsaturated molecules such as imines, bipy, carbodiimide, organic azides, hydrazine, and azo derivatives.

Formation of stable uranium(VI) colloidal nanoparticles in conditions relevant to radioactive waste disposal.

The favored pathway for disposal of higher activity radioactive wastes is via deep geological disposal. Many geological disposal facility designs include cement in their engineering design. Over the long term, interaction of groundwater with the cement and waste will form a plume of a hyperalkaline leachate (pH 10-13), and the behavior of radionuclides needs to be constrained under these extreme conditions to minimize the environmental hazard from the wastes. For uranium, a key component of many radioactive wastes, thermodynamic modeling predicts that, at high pH, U(VI) solubility will be very low (nM or lower) and controlled by equilibrium with solid phase alkali and alkaline-earth uranates. However, the formation of U(VI) colloids could potentially enhance the mobility of U(VI) under these conditions, and characterizing the potential for formation and medium-term stability of U(VI) colloids is important in underpinning our understanding of U behavior in waste disposal. Reflecting this, we applied conventional geochemical and microscopy techniques combined with synchrotron based in situ and ex situ X-ray techniques (small-angle X-ray scattering and X-ray adsorption spectroscopy (XAS)) to characterize colloidal U(VI) nanoparticles in a synthetic cement leachate (pH > 13) containing 4.2-252 μM U(VI). The results show that in cement leachates with 42 μM U(VI), colloids formed within hours and remained stable for several years. The colloids consisted of 1.5-1.8 nm nanoparticles with a proportion forming 20-60 nm aggregates. Using XAS and electron microscopy, we were able to determine that the colloidal nanoparticles had a clarkeite (sodium-uranate)-type crystallographic structure. The presented results have clear and hitherto unrecognized implications for the mobility of U(VI) in cementitious environments, in particular those associated with the geological disposal of nuclear waste.

Stable Uranium(VI) Methyl and Acetylide Complexes and the Elucidation of an Inverse Trans Influence Ligand Series

Thermally stable uranium(VI)-methyl and -acetylide complexes: U(VI)OR[N(SiMe3)2]3 R = -CH3, -C≡CPh were prepared in which coordination of the hydrocarbyl group is directed trans to the uranium-oxo multiple bond. The stability of the uranium-carbon bond is attributed to an inverse trans influence. The hydrocarbyl complexes show greater ITI stabilization than that of structurally related U(VI)OX[N(SiMe3)2]3 (X = F(-), Cl(-), Br(-)) complexes, demonstrated both experimentally and computationally. An inverse trans influence ligand series is presented, developed from a union of theoretical and experimental results and based on correlations between the extent of cis-destabilization, the complexes stabilities toward electrochemical reduction, the thermodynamic driving forces for U═O bond formation, and the calculated destabilization of axial σ* and π* antibonding interactions.

Thermally Stable Uranium Dinitrogen Complex with Siloxide Supporting Ligands

A new dinitrogen adduct of a homoleptic uranium tris(siloxide) complex, [U{OSi(Mes)3}3]2(μ-η2:η2-N2), is reported. Synthesis of the 15N-labeled isotopomer and Raman spectroscopy confirm the reductive activation of N2 to a (N2)2– dianion. The 15N NMR shift of the 15N2-labeled isotopomer is also reported. Crystallographic characterization shows a side-on (N2)2– coordinated in either an eclipsed or staggered conformation in different crystals. The U–N2–U complex is stable to vacuum and shows high thermal stability, retaining the formally reduced dinitrogen at 100 °C. The parent three-coordinate uranium(III) [U{OSi(Mes)3}3] could not be isolated in our hands, with N2-free syntheses affording only uranium(IV) compounds. The rational synthesis and full characterization of two such U(IV) byproducts, [U{OSi(Mes)3}{N(SiMe3)2}3] and [U{OSi(Mes)3}4], is also reported.