Hydrothermal synthesis of (Zr,U)SiO: an efficient pathway to incorporate uranium into zircon.

The preparation of synthetic (Zr,U)SiO solid solution is challenging, as the conventional high-temperature solid-state method limits the solubility of uranium (4 ± 1 mol%) in the orthosilicate phase due to its thermodynamic instability. However, these compounds are of great interest as a result of (Zr,U)SiO solid solutions, with uranium contents exceeding this concentration, being observed as corium phases formed during nuclear accidents. It has been identified that hydrothermal synthesis pathways can be used for the formation of the metastable phase, such as USiO.

Chronicles of plutonium peroxides: spectroscopic characterization of a new peroxo compound of Pu(IV).

Although hydrogen peroxide (HO) has been highly used in nuclear chemistry for more than 75 years, the preparation and literature description of tetravalent actinide peroxides remain surprisingly scarce. A new insight is given in this topic through the synthesis and thorough structural characterization of a new peroxo compound of Pu(IV).

Macrocyclic Ligand Coordinating Amide-Arm Hydrolysis Reaction Activation in Aqueous Solutions: Tetravalent Uranium Does It Better.

Chelation of lanthanide and actinide cations within a suitable macrocyclic ligand often results in a rigid, kinetically inert, and thermodynamically stable complex. A benchmark for such cation-ligand suitability are cyclen-derived macrocyclic ligands, frequently used as large cation hosts for various applications. Herein, a comprehensive study of the 1,4,7,10-tetrakis(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane ligand (DOTAM) chelates of U and Ce and their properties in aqueous solutions is presented.

How hydrothermal synthesis improves the synthesis of (Zr,Ce)SiO solid solutions.

Although ZrSiO is the most well-known compound in the zircon-structured family (space group 4/), the experimental conditions for preparing pure and well-crystallized phases that are doped with a tetravalent element hydrothermal synthesis have never been clearly discussed in the literature. With the aim to answer this question, the experimental conditions of the preparation of ZrSiO and (Zr,Ce)SiO were investigated in order to synthesize well-crystallized and pure phases. A multiparametric study has been carried out using soft hydrothermal conditions with variables including reactant concentration, initial pH of the reactive medium, and duration of the hydrothermal treatment.

Ultrasonically controlled synthesis of UO colloidal nanoparticles.

Actinide colloids and nanoparticles (NPs) currently constitute a topic of strong interest due to their potential role in advanced nuclear energetics and the environmental migration of radioactivity. A better understanding of the physico-chemical properties of nanoscale actinide oxides requires robust synthesis approaches. In this work, UO NPs were successfully prepared by sonochemistry from U(IV) solutions previously stabilised in a hydrochloric medium (20 kHz, 65 °C, Ar/(10%)CO).

Synthesis and multi-scale properties of PuO nanoparticles: recent advances and open questions.

Due to the increased attention given to actinide nanomaterials, the question of their structure-property relationship is on the spotlight of recent publications. Plutonium oxide (PuO) particularly plays a central role in nuclear energetics and a comprehensive knowledge about its properties when nanosizing is of paramount interest to understand its behaviour in environmental migration schemes but also for the development of advanced nuclear energy systems underway. The element plutonium further stimulates the curiosity of scientists due to the unique physical and chemical properties it exhibits around the periodic table.

First observation of [Pu(OH)O] cluster during the hydrolytic formation of PuO nanoparticles using H/D kinetic isotope effect.

New insights are provided about the formation mechanism of PuO nanoparticles (NPs) by investigating an unprecedented kinetic isotope effect observed during their hydrolytic synthesis in HO or DO and attributed to OH/OD zero point energy difference. The signature of a Pu(IV) oxo-hydroxo hexanuclear cluster, appearing as an important intermediate during the formation of the 2 nm PuO NPs (synchrotron SAXS/XAS), is further revealed indicating that their formation is controlled by H-transfer reactions occurring during hydroxo to oxo-bridge conversions.

DOTP versus DOTA as Ligands for Lanthanide Cations: Novel Structurally Characterized Ce and Ce Cyclen-Based Complexes and Clusters in Aqueous Solutions.

The coordination and redox chemistry of aqueous Ce macrocyclic compounds were studied by using the ligands DOTA and DOTP (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetraacetic acid and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetra(methylene phosphonic acid), respectively). The hydrolysis tendency of the tetravalent cation in the presence of DOTA is shown to result in the formation of a highly ordered, fluorite-like [Ce (O) (OH) (H O) (DOTAH) ] oxo-hydroxo structure both in solution and in the solid state. The lifetime of the analogous species formed in the presence of DOTP was found to be much shorter.

Pourbaix Diagram of Astatine Revisited: Experimental Investigations.

The Pourbaix diagram of an element displays its stable chemical forms with respect to the redox potential and pH of the solution, whose knowledge is fundamental for understanding and anticipating the chemistry of the element in a specified solution. Unlike most halogens, the Pourbaix diagram in the aqueous phase for astatine (At, = 85) is still under construction. In particular, the predominant domains of two astatine species assumed to exist under alkaline conditions, At and AtO(OH), need to be refined.

Dipolar and Contact Paramagnetic NMR Chemical Shifts in An Complexes with Dipicolinic Acid Derivatives.

Actinide +IV complexes (An = Th, U, Np, and Pu) with two dipicolinic acid derivatives (DPA and Et-DPA) have been studied by H and C NMR spectroscopies and first-principles calculations. The Fermi contact and dipolar contributions to the actinide-induced shifts (AIS) are evaluated from a temperature dependence analysis, combined with results. It allows an experimental estimation of the axial anisotropy of the magnetic susceptibility Δχ and of the hyperfine coupling constants of the NMR-active nuclei.

Correction: Formation of plutonium(IV) silicate species in very alkaline reactive media.

Correction for 'Formation of plutonium(IV) silicate species in very alkaline reactive media' by Paul Estevenon , , 2021, , 12528-12536, DOI: 10.1039/D1DT02248B.

Characterization of a Hexanuclear Plutonium(IV) Nanostructure in an Acetate Solution via Visible-Near Infrared Absorption Spectroscopy, Extended X-ray Absorption Fine Structure Spectroscopy, and Density Functional Theory.

A new hexanuclear plutonium cluster has been stabilized in aqueous media with acetate ligands. To probe the formation of such a complex structure, visible-near infrared (vis-NIR) absorption spectroscopy, extended X-ray absorption fine structure (EXAFS) spectroscopy, and density functional theory (DFT) were combined. The presence of PuO(OH)(CHCOO) species in solution was first detected by vis-NIR and EXAFS spectroscopy.

X-ray absorption spectroscopy and actinide electrochemistry: a setup dedicated to radioactive samples applied to neptunium chemistry.

A spectroelectrochemical setup has been developed to investigate radioactive elements in small volumes (0.7 to 2 ml) under oxidation-reduction (redox) controlled conditions by X-ray absorption spectroscopy (XAS). The cell design is presented together with in situ XAS measurements performed during neptunium redox reactions.

Reactions of methyl, hydroxyl and peroxyl radicals with the DOTA chelating agent used in medical imaging.

The mechanism of reaction of DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) with ·CH, CHO· and ·OH radicals were studied. The radicals were formed in situ radiolytically. The methyl radicals react orders of magnitude slower with DOTA and with M(DOTA) than the hydroxyl radicals.

Formation of plutonium(IV) silicate species in very alkaline reactive media.

Studying the speciation of Pu(IV) in very alkaline and silicate ion rich reactive media allowed identification of the formation of plutonium(IV)-silicate colloidal suspensions which were stable for months. These colloids were stabilized in aqueous solution for pH > 13 and for concentrations around 10 mol L. Successive filtration processes allowed evaluation of their size, which was found to be smaller than 6 nm.

Ultrasonically assisted conversion of uranium trioxide into uranium(vi) intrinsic colloids.

Under oxidizing conditions, the corrosion of spent nuclear fuel may lead to the leaching of radionuclides including soluble uranyl-based species. The speciation of the generated chemical forms is complex and the related potential formation of colloidal species appears surprisingly poorly reported in the literature. Their formation could however contribute significantly to the mobility of radionuclides in the environment.

A 70-Year-Old Mystery in Technetium Chemistry Explained by the New Technetium Polyoxometalate [H O ] [Tc O ] ⋅ 4H O.

[H O ] [Tc O ] ⋅ 4H O [1] was prepared from an aqueous Tc O solution concentrated over anhydrous H SO . [Tc O ] is the first polyanionic species to be reported for Tc. The unit cell contains one centrosymmetric [Tc O ] polyanion as well as hydronium ions and water molecules.

Oligomers Intermediates in Between Two New Distinct Homonuclear Uranium(IV) DOTP Complexes*.

Two new aqueous U complexes were synthesized by the interaction between the tetravalent uranium cation and the (1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetra(methylene phosphonic acid) (DOTP) macrocyclic ligand. Two distinct homonuclear complexes were identified; the first was characterized by X-ray crystallography as a unique "out-of-cage", [U(DOTPH ) ] complex, in which the U cation is octa-coordinated to 4 phosphonic arms from each ligand in a square anti-prism geometry, with a C symmetry. The second is the "in-cage" [U(DOTPH )] complex, in which the tetravalent cation is located between the macrocycle O and N planes.

Real-Time Observation of Solvation Dynamics of Electron in Actinide Extraction Binary Solutions of Water and -Tributyl Phosphate.

The excess electron in solution is a highly reactive radical involved in various radiation-induced reactions. Its solvation state critically determines the subsequent pathway and rate of transfer. For instance, water plays a dominating role in the electron-induced dealkylation of -tributyl phosphate in actinide extraction processing.

Redox Properties of CeDOTA in Carbonated Aqueous Solutions. A Radiolytic and an Electrochemical Study.

The redox chemistry of CeDOTA in carbonate solutions was studied using electrochemistry and radiolysis techniques (continuous radiolysis and pulse radiolysis). Spectroscopic measurements point out that the species present in the solutions at high bicarbonate concentrations are [CeDOTA(CO)] (or less plausible [CeDOTA(HCO)]) with the carbonate (bicarbonate) anion as the ninth ligand versus [CeDOTA(HO)] present in the absence of bicarbonate. Electrochemical results show a relatively low increase in the thermodynamic stabilization of the redox couple Ce in the presence of carbonate versus its aqueous analogue.

Temperature Dependence of H Paramagnetic Chemical Shifts in Actinide Complexes, Beyond Bleaney's Theory: The An O -Dipicolinic Acid Complexes (An=Np, Pu) as an Example.

Actinide +VI complexes ( = , and ) with dipicolinic acid derivatives were synthesized and characterized by powder XRD, SQUID magnetometry and NMR spectroscopy. In addition, and complexes were described by first principles CAS based and two-component spin-restricted DFT methods. The analysis of the H paramagnetic NMR chemical shifts for all protons of the ligands according to the X-rays structures shows that the Fermi contact contribution is negligible in agreement with spin density determined by unrestricted DFT.

study of the synthesis of thorite (ThSiO) under environmental representative conditions.

Thorite, (ThSiO4) with a zircon type structure, is one of the most abundant natural sources of thorium on Earth. Generally, actinides are known to form nanoparticles in silicate medium, though no direct link between those colloids and the crystalline form of thorite was evidenced until now. Here we show the formation of thorite from colloids and nanocrystalline structures under experimental conditions close to environmental pH and temperature.

Sonochemical dissolution of nanoscale ThO and partial conversion into a thorium peroxo sulfate.

The influence of the sample morphology and experimental conditions towards the sonochemical dissolution of nanoscale ThO samples in sulfuric acid media is described. Significant sonochemical dissolution rates and yields are observed at 20 kHz under Ar/O atmosphere in dilute 0.5 M HSO at room temperature, contrasting with the generally-reported high refractory behavior for ThO.

Crystallographic structure and crystal field parameters in the [An(DPA)] series, An = Th, U, Np, Pu.

The [AnIV(DPA)3]2- series with An = Th, U, Np, Pu has been synthesized and characterized using SC-XRD and vibrational spectroscopy. First principles calculations were performed, the total electron density is analyzed using the Quantum Theory of Atoms in Molecules. Crystal field parameters and strength parameters are deduced following a previous work on the LnIII analog series e.