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Although hydrogen peroxide (H 2 O 2 ) 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).

Historic perspectives describing f-elements as being redox "inactive" are fading. Researchers continue to discover new oxidation states that are not as inaccessible as once assumed for actinides and lanthanides. Inspired by those contributions, we studied americium(III) oxidation in aqueous media under air using NaBiO 3( s ) . We identified selective oxidation of Am 3+ ( aq ) to AmO 2 2+ ( aq ) or AmO 2 1+ ( aq ) could be achieved by changing the aqueous matrix identity. AmO 2 2+ ( aq ) formed in H 3 PO 4( aq ) (1 M) and AmO 2 1+ ( aq ) formed in dilute HCl ( aq ) (0.1 M). These americyl products were stable for weeks in solution. Also included is a method to recover 243 Am from the americium and bismuth mixtures generated during these studies.

The positive impact of having access to well-defined starting materials for applied actinide technologies - and for technologies based on other elements - cannot be overstated. Of numerous relevant 5f-element starting materials, those in complexing aqueous media find widespread use. Consider acetic acid/acetate buffered solutions as an example. These solutions provide entry into diverse technologies, from small-scale production of actinide metal to preparing radiolabeled chelates for medical applications. However, like so many aqueous solutions that contain actinides and complexing agents, 5f-element speciation in acetic acid/acetate cocktails is poorly defined. Herein, we address this problem and characterize Ac 3+ and Cm 3+ speciation as a function of increasing acetic acid/acetate concentrations (0.1 to 15 M, pH = 5.5). Results obtained via X-ray absorption and optical spectroscopy show the aquo ion dominated in dilute acetic acid/acetate solutions (0.1 M). Increasing acetic acid/acetate concentrations to 15 M increased complexation and revealed divergent reactivity between early and late actinides. A neutral Ac(H 2 O) 6 (1) (O 2 CMe) 3 (1) compound was the major species in solution for the large Ac 3+ . In contrast, smaller Cm 3+ preferred forming an anion. There were approximately four bound O 2 CMe 1- ligands and one to two inner sphere H 2 O ligands. The conclusion that increasing acetic acid/acetate concentrations increased acetate complexation was corroborated by characterizing (NH 4 ) 2 M(O 2 CMe) 5 (M = Eu 3+ , Am 3+ and Cm 3+ ) using single crystal X-ray diffraction and optical spectroscopy (absorption, emission, excitation, and excited state lifetime measurements)., Competing Interests: The authors have no conflicts of interest with this work., (This journal is © The Royal Society of Chemistry.)

Increasing access to the short-lived α-emitting radionuclide astatine-211 ( 211 At) has the potential to advance targeted α-therapeutic treatment of disease and to solve challenges facing the medical community. For example, there are numerous technical needs associated with advancing the use of 211 At in targeted α-therapy, e.g., improving 211 At chelates, developing more effective 211 At targeting, and characterizing in vivo 211 At behavior. There is an insufficient understanding of astatine chemistry to support these efforts. The chemistry of astatine is one of the least developed of all elements on the periodic table, owing to its limited supply and short half-life. Increasing access to 211 At could help address these issues and advance understanding of 211 At chemistry in general. We contribute here an extraction chromatographic processing method that simplifies 211 At production in terms of purification. It utilizes the commercially available Pre-Filter resin to rapidly (<1.5 h) isolate 211 At from irradiated bismuth targets (Bi decontamination factors ≥876 000), in reasonable yield (68-55%) and in a form that is compatible for subsequent in vivo study. We are excited about the potential of this procedure to address 211 At supply and processing/purification problems.

Actinide research at the nanoscale is gaining fundamental interest due to environmental and industrial issues. The knowledge of the local structure and speciation of actinide nanoparticles, which possibly exhibit specific physico-chemical properties in comparison to bulk materials, would help in a better and reliable description of their behaviour and reactivity. Herein, the synthesis and relevant characterization of PuO 2 and ThO 2 nanoparticles displayed as dispersed colloids, nanopowders, or nanostructured oxide powders allow to establish a clear relationship between the size of the nanocrystals constituting these oxides and their corresponding An(iv) local structure investigated by EXAFS spectroscopy. Particularly, the first oxygen shell of the probed An(iv) evidences an analogous behaviour for both Pu and Th oxides. This observation suggests that the often observed and controversial splitting of the Pu-O shell on the Fourier transformed EXAFS signal of the PuO 2 samples is attributed to a local structural disorder driven by a nanoparticle surface effect rather than to the presence of PuO 2+ x species., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Fundamental knowledge on intrinsic plutonium colloids is important for the prediction of plutonium behaviour in the geosphere and in engineered systems. The first synthetic route to obtain salt-free intrinsic plutonium colloids by ultrasonic treatment of PuO 2 suspensions in pure water is reported. Kinetics showed that both chemical and mechanical effects of ultrasound contribute to the mechanism of Pu colloid formation. In the first stage, fragmentation of initial PuO 2 particles provides larger surface contact between cavitation bubbles and solids. Furthermore, hydrogen formed during sonochemical water splitting enables reduction of Pu(IV) to more soluble Pu(III), which then re-oxidizes yielding Pu(IV) colloid. A comparative study of nanostructured PuO 2 and Pu colloids produced by sonochemical and hydrolytic methods, has been conducted using HRTEM, Pu L III -edge XAS, and O K-edge NEXAFS/STXM. Characterization of Pu colloids revealed a correlation between the number of Pu-O and Pu-Pu contacts and the atomic surface-to-volume ratio of the PuO 2 nanoparticles. NEXAFS indicated that oxygen state in hydrolytic Pu colloid is influenced by hydrolysed Pu(IV) species to a greater extent than in sonochemical PuO 2 nanoparticles. In general, hydrolytic and sonochemical Pu colloids can be described as core-shell nanoparticles composed of quasi-stoichiometric PuO 2 cores and hydrolyzed Pu(IV) moieties at the surface shell.

The influence of the ultrasonic frequency (20 kHz, 207 kHz, and 615 kHz) towards the formation kinetics of H2O2 under Ar and Ar/(20 vol.%)O2 atmospheres was evaluated in pure water and aqueous nitric solutions. Results obtained at low frequency ultrasound demonstrate that hydrogen peroxide formation is enhanced under an Ar/O2 gas mixture whatever the sonicated medium. Nevertheless, H2O2 yields are higher in aqueous nitric solutions whatever the nature of the saturating gas. These observations are consistent at high frequency ultrasound under Ar gas notwithstanding higher yields for H2O2. Surprisingly, an inverse tendency is observed for high frequency sonolysis carried out under an Ar/O2 atmosphere: higher yields of H2O2 are measured in pure water. Further studies in the presence of pure Ar revealed a more important decomposition of nitric acid under high frequency ultrasound leading to higher yields of both HNO2 in the liquid phase and NO in the gas phase. In the presence of Ar/O2 mixture, the intrabubble oxidation of NO causes cavitation bubble depletion in O2 leading to the drop of H2O2 yield. On the other hand, it was found that for Ar/(20 vol.%)O2 mixture there is no influence of oxygen on HNO2 yield whatever the ultrasonic frequency; this is most likely explained by two processes: (i) HNO2 formation results from nitrate-ion thermolysis in the liquid reaction zone surrounding the cavitation bubble, and (ii) effective intrabubble oxidation of NOx species by oxygen to nitrate-ion., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Maintaining nanoparticle properties when scaling up a chemical synthesis is challenging due to the complex interplay between reducing agents and precursors. A sonochemical synthesis route does not require the addition of reducing agents as they are instead being continuously generated in-situ by ultrasonic cavitation throughout the reactor volume. To optimize the sonochemical synthesis of nanoparticles, understanding the role of radical scavengers is paramount. In this work we demonstrate that optimum scavenger concentrations exist at which the rate of Ag-nanoparticle formation is maximized. Titanyl dosimetry experiments were used in conjunction with Ag-nanoparticle formation rates to determine these optimum scavenger concentrations. It was found that more hydrophobic scavengers require lower optimum concentrations with 1-butanol < 2-propanol < ethanol < methanol < ethylene glycol. However, the optimum concentration is shifted by an order of magnitude towards higher concentrations when pyrolytic decomposition products contribute to the reduction. The reduction rate is also enhanced considerably. [ABSTRACT FROM AUTHOR]

Reducing the amount of noble metals in catalysts for electrochemical conversion devices is paramount if these devices are to be commercialized. Taking advantage of the high degree of particle property control displayed by the sonochemical method, we set out to synthesize Cu@Pt bimetallic nanocatalysts in an effort to improve the mass activity towards the hydrogen evolution reaction. At least 17 times higher mass activity was found for the carbon supported Cu@Pt bimetallic nanocatalyst (737 mA mg−1, E = − 20   m V) compared to carbon supported Pt nanocatalysts prepared with the same ultrasound conditions (44 mA mg−1, E = − 20   m V). The synthesis was found to proceed with the sonochemical formation of Cu and Cu2O nanoparticles with the addition of PtCl4 leading to galvanic displacement of the Cu-nanoparticles and the formation of a Pt-shell around the Cu-core. [ABSTRACT FROM AUTHOR]

Extraction mechanisms of two bifunctional extractants which differ only by the grafting of an alkyl chain between their two functions were investigated at molecular and supramolecular scales to investigate the origin of their very different separation factors toward uranium and zirconium. Investigation of the complex structure with spectroscopic analysis (Fourier Transform Infra-Red (FTIR), ElectroSpray Ionization Mass Spectroscopy (ESI-MS) and Extended X-Ray Absorption Fine Structure (EXAFS)) demonstrated that alkylation does not affect the chelation mechanism of uranium and zirconium. Stoichiometries of complexes remain identical for both extractants: UO2L2(NO3)2 and zirconium polynuclear complexes are formed after extraction into the organic phase. The origin of selectivity was therefore investigated by considering the supramolecular self-assembly of the two bifunctional molecules. Small-Angle X ray and Neutrons Scattering (SAXS and SANS) showed that the highest separation factors between U and Zr are obtained when smaller aggregates are formed. The results of this study therefore suggests that the selectivity is controlled by the supramolecular self-assembly of the two extractant molecules. Thanks to a smaller packing parameter, the non-alkylated molecule forms bigger aggregates analogous to reverse micelles that can extract additional polar species in their polar core through a solubilization effect, thus decreasing the separation factor between uranium and zirconium. [ABSTRACT FROM AUTHOR]

Sonochemistry studies chemical and physical effects in liquids submitted to power ultrasound. These effects arise not from a direct interaction of molecules with sound waves, but rather from the acoustic cavitation: the nucleation, growth, and implosive collapse of microbubbles in liquids submitted to power ultrasound. The violent implosion of bubbles leads to the formation of chemically reactive species. In principle, each cavitation bubble can be considered as a microreactor initiating chemical reactions at mild conditions. In addition, microjets and shock waves accompanied bubble collapse produce fragmentation, dispersion and erosion of solid surfaces or particles. Microbubbles oscillating in liquids also enable nucleation and precipitation of nanosized actinide compounds with specific morphology. This review focuses on the versatile sonochemical processes with actinide ions and particles in homogenous solutions and heterogenous systems. The redox reactions in aqueous solutions, dissolution or precipitation of refractory solids, synthesis of actinide nanoparticles, and ultrasonically driving decontamination are considered. The guideline for further research is also discussed. [ABSTRACT FROM AUTHOR]

Among the fission products present in the spent nuclear fuel, technetium exhibits a singular behavior in reprocessing operations performed by solvent extraction. Indeed, this strong acid readily dissociates to form the oxo-anion TcO4− that may interfere with uranium(VI), plutonium(IV), and zirconium(IV) in the extraction cycles of the PUREX process. This paper focuses on the uranium-technetium complex with TBP and on its non-radioactive rhenium surrogate. Despite the large set of distribution data available for rhenium and technetium extraction with TBP, the structures of the co-extracted complexes remain largely unknown. However, it is important to understand clearly the extraction mechanism of technetium with TBP in the PUREX process to optimize the separation process and to model its behavior during the extraction steps. Based on distribution data available in the literature, a thermodynamic model was developed for the extraction of technetium with TBP for a large excess of uranium(VI) in organic phase. A good representation of uranium and technetium distribution data was thus obtained when considering the formation of (HTcO4)(TBP)n complexes, as well as mixed UO2(NO3)(TcO4)(HNO3)x(TBP)n, complexes. In the complex UO2(NO3)2(HNO3)x(TBP)n., one pertechnetate anion replaces one nitrate in the uranium coordination sphere. Combination of complementary spectroscopic techniques (FT-IR and X-ray absorption) supported by theoretical calculations (density functional theory) with organic phases containing a large excess of technetium(VII) or rhenium(VII) enabled full characterization of the limit mixed uranium−technetium species and also of mixed uranium-rhenium species. Details on the coordination of the uranium-technetium complex are provided with the help of DFT calculations and XAS measurements. [ABSTRACT FROM AUTHOR]

The efficacy of photocatalysis strongly depends on the activity of the catalysts and the operational factors, especially factors associated with mass transfer and the possibility of catalyst deactivation. The use of ultrasound has great potential to enhance catalyst activity, during both the synthesis and actual oxidation processes due to the cavitational effects of turbulence and liquid streaming. This article presents an overview of the application aspects of ultrasound, both in the synthesis of the photocatalyst and applications for wastewater treatment. A review of the literature revealed that the use of ultrasound in the synthesis processes can result in a catalyst with a lower mean size and higher surface area as well as uniform size distribution. The application of ultrasound in the actual photocatalytic oxidation facilitates enhancement of the oxidation capacity, leading to higher degradation rates, sometimes synergistic results and definitely lower treatment times. This article also presents guidelines for the selection of the best operating conditions for the use of ultrasound in photocatalytic systems and includes a discussion on the possible reactor configurations suitable for large-scale operations. Overall, a combination of ultrasound with photocatalytic oxidation or the optimized application of ultrasound in catalyst synthesis can yield significant benefits. [ABSTRACT FROM AUTHOR]

There is significant interest in reducing the timeline for post detonation nuclear debris examination. A critical need is rapid dissolution of refractory nuclear debris to facilitate measurement of key radioisotopes and isotope ratios. Field deployable, rapid dissolution and analysis methods could significantly shorten the attribution analysis timeline. The current practice uses HF in combination with other acids to attack silicates and other refractory minerals expected in debris samples. However, techniques requiring HF are not amenable to use in the field. The fluorinating agent ammonium bifluoride (ABF) is a potential field deployable substitute for HF. In this work we report on the use of in-direct sonication with ABF as a means to improve low-temperature acid digestion of seven USGS and NIST geological reference materials. Using this method, elemental recoveries for USGS reference materials DNC-1a Dolerite, QLO-1a Quartz Latite, SDC-1 Mica Schist, and BHVO-2 Hawaiian Basalt were quantitative while the recovery of elements in USGS AGV-2 Andesite and NIST SRM 278 Obsidian and 1413 High Alumina Sand were low. [ABSTRACT FROM AUTHOR]