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Sonochemistry was used for the preparation of uranium oxide nanoparticles. In comparison to classical hydrolysis approach, larger, better defined and more crystalline UO2+xnanoparticles were observed under ultrasound.

New insights are provided about the formation mechanism of PuO

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

Splitting of water molecules driven by ultrasound plays a central role in sonochemistry. While studies of sonoluminescence revealed the formation of a plasma inside the cavitation bubble, much less is known about the contribution of plasma chemical processes to the sonochemical mechanisms. Herein, we report for the first time sonochemical processes in water saturated with pure CO. The presence of CO causes a large increase in the H/D kinetic isotope effect (KIE) to α

The aim of the article is to attempt to identify the profound changes taking place in the global and Russian energy sectors. One of the key drivers of the new development paradigm is the active implementation of the Industry 4.0 project elements in the fuel and energy complex, which is comprehensive and relies on digital technologies. The features of the global innovation project “Industry 4.0” and, in particular, the digitalization of the oil and gas sector were studied. The possibility of transition of the Russian energy complex to a new development paradigm is also analyzed, it consists in the implementation of elements of the Industry 4.0 project. The problems of the Russian energy sector on the transition to a new development model, which are associated with the features of its production, market and institutional structures, are identified. The theory of value chains in the fuel and energy complex and its upgrade is separately studied. The main niche in the Russian energy sector is highlighted, in which the development of the Industry 4.0 paradigm is possible. Nore: The paper is an extended version of the article presented at the conference SGEM Vienna Green 2019 Conference (9-11 December, 2019), Austria. Reference citation: https://doi.org/10.5593/sgem2019V/1.4The title, abstract was changed in the article / The degree of knowledge of the chains added in the fuel and energy complex was also considered — 3- 4 pp.

International audience; Fundamental knowledge about plutonium intrinsic colloids is a key issue for the prediction of plutonium transport and release rates in the environment. Recent studies demonstrated that the particle size and surface properties of intrinsic Pu colloids are strongly influenced by the preparation method. In this work, a combination of synchrotron small angle X-ray scattering (SAXS) with X-ray absorption spectroscopy (XAS) is used to characterize two kinds of stable plutonium intrinsic colloids prepared by hydrolysis of Pu(IV) ionic species and sonolysis of PuO2 in pure water. Despite their similarities, the multi-scale structural properties of these colloidal suspensions are found to be strongly influenced by the synthesis route. The hydrolysis approach leads to spherical nanoparticles of ca. 2.0 nm, whereas sonolytic colloids show elongated structures measuring 5.7 nm of thickness and >30 nm long. This difference results from the synthesis mechanism and can be attributed to nanoparticle aggregation in the absence of capping-ions. The results obtained by both SAXS and XAS approaches converge in the description of Pu(IV) intrinsic colloids as core–shell nanoparticles made up of a PuO2 core covered with a disordered Pu–O shell characterized by a splitting of Pu–O and Pu–Pu distances and an associated strong increase of associated DWF parameters. The local distortions of both Pu–O and Pu–Pu coordination spheres observed by XAS seem to be correlated with the nanoparticle shrinking probed by SAXS rather from the contribution of higher Pu oxidation states. The stabilization of the hydrolytic colloidal particles is further suggested from SAXS simulation to result from interaction with counter-ions from the medium.

The paper offers an analysis of the problems and prospects of the most difficult branch of the Russian economy, i.e. coal industry. An attempt is made to find directions for diversifying the economy of a coal region. The authors suggested turning to the theory of value chains. The coal industry is the beginning of a chain of added value formation. The study confirmed the possibility of cooperation with the engineering industry for building new technological chains. The analysis also made it possible to put forward a hypothesis that localization on the territory of processing industries, based on related technologies within the framework of modern elongated and ramified supply chains and value chains, can become an instrument for overcoming "enclave" and reducing resource dependence of regions. Based on the analysis of patent sources, the authors defined the main directions of development of the coal industry that are currently in the focus of attention of the leading coal-mining countries and companies. On the basis of scientific research and design, the authors use the example of the Kemerovo region to determine the degree of technological development of the supported patents and the level of companies' readiness for joint projects with the machine-building industry.

The influence of the sample morphology and experimental conditions towards the sonochemical dissolution of nanoscale ThO

International audience; Hierarchically porous materials offer the opportunity for catalyst development in regards to improving catalytic performances. In the present work, the combination of latex synthesis, sonochemical reduction and two-step catalysed sol–gel process has been demonstrated to be a versatile method for preparing supported catalysts with tailored hierarchical porosity. This method has been used to prepare porous Pt/SiO2 catalysts with mesopore and macropore size ranges as large as 2–15 nm and 90–400 nm, respectively. These hierarchically porous catalysts presented an excellent catalytic performance for the selective hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CAN). Selectivity values up to 100% at 80% conversion of p-CNB and initial reaction rates up to 74.0 molCNB/min molPt were obtained, while a commercial catalyst exhibited both a lower selectivity of 90.8% and a lower initial reaction rate of 47.7 molCNB/min molPt.

The production of hydrogen peroxide H 2 O 2 , as an important commodity chemical, attires the attention towards greener processes such as the direct synthesis from hydrogen H 2 and oxygen O 2 , the selectivity being the biggest challenge. Since this reaction is structure-sensitive, the design of appropriate catalysts is required. We propose a novel method to prepare hierarchically porous Pd/SiO 2 catalyst by combination of miniemulsion polymerisation to prepare a Pd-containing latex template and sol-gel synthesis in controlled conditions to tailor the silica porosity. The final material displayed a surface area of 711 m 2 g −1 and a total pore volume of 0.93 cm 3 g −1 . The catalyst was evaluated with different pre-treatments in the direct synthesis of H 2 O 2 , where it exhibited structural resistance at the reaction conditions and a stable selectivity of 46 ± 1% towards H 2 O 2 .

As a follow-up of the paper “Engineering of silica-supported platinum catalysts with hierarchical porosity combining latex synthesis, sonochemistry and sol-gel process – I. Material preparation” (A.F. Sierra-Salazar, et at., Microporous Mesoporous Mater. 234 (2016) 207–214. http://dx.doi.org/10.1016/j.micromeso.2016.07.009 ), we propose waterborne Pt-based catalysts with hierarchical porosity and controlled Pt nanoparticles (NPs) distribution within the support. The materials exhibit specific surface areas and total pore volumes as high as 490 m 2 g −1 and 0.77 cm 3 g −1 , with ∼5 nm Pt NPs mainly located in the macropores. The Pt NPs were characterised using X-ray photoemission spectroscopy (XPS) and high resolution transmission electron microscopy (HR-TEM). Considering the selectivity challenge of the catalytic hydrogenation of halonitrobenzenes to produce haloanilines, which are important raw materials for several industrial products, we evaluated these hierarchically porous catalysts for the hydrogenation of p -chloronitrobenzene ( p -CNB) in batch mode to produce p -chloroaniline ( p -CAN). It was possible to obtain up to 100% selectivity at 80% conversion and initial reaction rates up to 34 mol CNB min −1 mol Pt −1 . Such selectivity was higher than that exhibited by a commercial Pt/SiO 2 catalyst (up to 92%).

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

International audience; In this work, the sonoluminescence of NH radicals has been evaluated as a new spectroscopic probe for the nonequilibrium plasma produced by multibubble cavitation in liquids. The experiments were performed in aqueous ammonia solutions subjected to power ultrasound at low and high frequencies and under two different rare gases (Ar and Xe). Sonoluminescence (SL) spectroscopy focuses on the emission of the two present systems: NH (A 3 P-X 3 S À) and OH (A 2 S +-X 2 P). Both spectroscopic systems indicate the absence of thermal equilibrium during bubble collapse (T v 4 T r) irrespective of the saturating gas. When Ar is used as the saturating gas, these emissions can be fitted using Specair software and the corresponding rovibronic temperatures are derived. Both species indicate a net increase in vibrational temperatures with the US frequency. In Xe, the SL spectra exhibit OH (C 2 S +-A 2 S +) and NH (c 1 P-a 1 D) emission bands indicating a higher electron temperature compared to Ar. However, in Xe, the SL spectra cannot be satisfactorily fitted because of significant line broadening. The estimation of the intrabubble pressure via SL simulation using Specair software is discussed. Monitoring of the sonochemical activity indicates the formation of H 2 and N 2 H 4 , while no H 2 O 2 accumulates under these conditions. In the presence of Xe, NO is also formed as a sonolysis product. The appearance of new possible reaction pathways under Xe is made possible by the higher plasma electron density and correlates with SL data.

The article attempts to identify the profound changes occurring in the global and Russian energy sectors under the conditions of Industry 4.0. The features of the implementation of the global innovative Industry 4.0 project in the global energy sector are studied; a change in the technological basis, an upgrade of value chains and a change in business models are shown. The state and prospects of the Russian fuel and energy complex transition to a new Industry 4.0 development paradigm are analyzed. The main models and barriers to the formation of new value chains in the Russian fuel and energy complex are identified. The main niche in the Russian energy complex is highlighted, in which its development on the principles of the Industry 4.0 paradigm is possible and most likely.

Sonoluminescence (SL) spectra of a very dry [BEPip][NTf

PuO2 is considered an important material for current and future nuclear fuel; however it is a very refractive compound towards dissolution. Among other techniques, its reprocessing can be performed via complexing dissolution in concentrated and boiling nitric acid containing hydrofluoric acid, or via oxidant dissolution in the presence of reagents with redox couples having high potentials such as Ce(iv)/Ce(iii), or Ag(ii)/Ag(i). Reductive dissolution can be performed under softer conditions and is considered an alternative to these methods which may suffer from several drawbacks (corrosion, effluent management, compatibility with nuclear waste disposal, etc.). In this study, a sonochemical and reductive approach is investigated for PuO2 dissolution under relatively mild conditions. At the first stage, the experiments are performed with CeO2 as an inactive surrogate for PuO2. The quantitative dissolution of both oxides can be achieved under ultrasound (20 kHz, 0.35-0.70 W mL(-1)) in 0.5 M HNO3/0.1 M [N2H5NO3]/2 M HCOOH sparged with Ar at 33-35 °C in the presence of Ti particles as a generating source of reductive species. Ultrasound enables the depassivation of the Ti surface (usually strongly passivated in nitric solutions) through acoustic cavitation which then allows further generation of the intermediate Ti(iii) reductive species. Dissolution rates and yields can be further increased with the injection of dilute fluoride aliquots (NH4F or HF) in the sonicated solution to favor Ti chemical depassivation. The rapid and complete dissolution of PuO2 under selected conditions is accompanied by Pu(iii) accumulation in solution.

Ultrasonic frequency is a key parameter determining multibubble sonoluminescence (MBSL) spectra of water saturated with Ar/O2 gas mixtures. At 20 kHz, the MBSL is quenched by oxygen. By contrast, at high-frequency ultrasound the maximal MBSL intensity is observed in the presence of Ar/20%O2 gas mixture. Nevertheless, oxygen has no influence on the shape of MBSL spectra. The effect of oxygen on MBSL is explained by oxygen dissociation inside the collapsing bubble which is much more effective at high ultrasonic frequency compared to 20 kHz ultrasound. In contrast to MBSL, a higher yield of H2O2 is observed in Ar/20%O2 gas mixture whatever the ultrasonic frequency. At 20°C and 20% of oxygen the maximal yield of H2O2 is observed at 204-362 kHz. The maximal yield of H2O2 is shifted to 613kHz when the bulk temperature is raised up to 40°C. Coupling of high-frequency ultrasound with mechanical stirring and intensive Ar/O2 bubbling improves H2O2 production. Comparison of MBSL and sonochemistry allowed to conclude that H2O2 is formed from non-excited OH (X(2)Π) and HO2 radicals. Finally, it was shown that at the studied conditions the efficiency of ultrasonic degassing is hardly influenced by frequency.

In order to treat aqueous effluents containing organic pollutants, several techniques can be considered depending on the organic compound concentration. Sonochemistry appears to be a promising solution to answer water remediation issue. In fact, when submitted into a liquid, ultrasound can induce the nucleation, growth, and violent collapse of vapor/gas filled bubbles. However, despite the extreme local conditions observed during acoustic cavitation, using ultrasound alone is efficient only at low concentration in organic pollutants. In the present study, 0.05 M oxalic acid degradation kinetics were followed at 40 °C under various conditions, in presence or not of Pt/TiO2 catalyst under silent conditions or ultrasound at 20 and 360 kHz. Experiments were achieved under controlled atmosphere and comparison between argon, Ar/O2 (20 vol% O2) and pure O2 conditions was performed. Oxidation rate increase of oxalic acid was measured under Ar/O2 atmosphere in presence of Pt/TiO2 catalyst due to strong dispersion effect of both low and high ultrasonic frequency and formation of chemically active species by sonolysis. High frequency ultrasonic irradiation under Ar/O2 atmosphere gives the highest kinetic increase compared to silent conditions with oxalic acid degradation rate around 13 μmol min−1 at 40 °C with 2 g L−1 of 3 wt% Pt on P25 TiO2 catalyst.

In this work, the sonoluminescence of NH radicals has been evaluated as a new spectroscopic probe for the nonequilibrium plasma produced by multibubble cavitation in liquids. The experiments were performed in aqueous ammonia solutions subjected to power ultrasound at low and high frequencies and under two different rare gases (Ar and Xe). Sonoluminescence (SL) spectroscopy focuses on the emission of the two present systems: NH (A

Porous (Ce 0.5 Zr 0.5 )O 2 solid solutions were prepared by thermolysis ( T = 285 °C) or sonolysis (20 kHz, I = 32 W cm −2 , P ac = 0.46 W mL −1 , T = 200 °C) of Ce(III) and Zr(IV) acetylacetonates in oleylamine or hexadecylamine under argon followed by heat treatment of the precipitates obtained in air at 450 °C. Transmission Electron Microscopy images of the samples show nanoparticles of ca. 4–6 nm for the two synthetic approaches. The powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray and μ-Raman spectroscopy of solids obtained after heat treatment indicate the formation of (Ce 0.5 Zr 0.5 )O 2 solid solutions with a metastable tetragonal crystal structure for the two synthetic routes. The specific surface area of the samples varies between 78 and 149 m 2 g −1 depending on synthesis conditions. The use of Barrett–Joyner–Halenda and t -plot methods reveal the formation of mixed oxides with a hybrid morphology that combines mesoporosity and microporosity regardless of the method of preparation. Platinum nanoparticles were deposited on the surface of the mixed oxides by sonochemical reduction of Pt(IV). It was found that the materials prepared by sonochemistry exhibit better resistance to dissolution during the deposition process of platinum. X-ray photoelectron spectroscopy analysis shows the presence of Pt(0) and Pt(II) on the surface of mixed oxides. Porous (Ce 0.5 Zr 0.5 )O 2 mixed oxides loaded with 1.5 %wt. platinum exhibit high activity in catalytic wet air oxidation of formic acid at 40 °C.

International audience; Sonoluminescence spectra collected from 0.1 to 3.0 M aqueous solutions of formic acid sparged with argon show the OH(A2Σ+−X2Πi) and C2(d3Πg → a3Πu) emission bands and a broad continuum typical for multibubble sonoluminescence. The overall intensity of sonoluminescence and the sonochemical yield of HCOOH degradation vary in opposite directions: the sonoluminescence is quenched while the sonochemical yield increases with HCOOH concentration. By contrast, the concentration of formic acid has a relatively small effect on the intensity of C2 Swan band. It is concluded that C2 emission originates from CO produced by HCOOH degradation rather than from direct sonochemical degradation of HCOOH. The intensity of C2 band is much stronger at high ultrasonic frequency compared to 20 kHz ultrasound which is in line with higher yields of CO at high frequency. Another product of HCOOH sonolysis, carbon dioxide, strongly quenches sonoluminescence, most probably via collisional non-radiative mechanism.

This study reported the sonochemical deposition of platinum on the surface of polystyrene beads (PSBs) and the transfer of obtained Pt nanoparticles into a porous silica matrix using the PSB as a sacrificial template. Platinum nanoparticle deposition was ensured by the sonochemical reduction of Pt(IV) at room temperature in latex solutions containing polystyrene beads in the presence of formic acid under Ar or under Ar/CO atmosphere without any additives. After ultrasonic treatments for few hours, well dispersed Pt nanoparticles within the range of 3-5 nm deposited on PSB were obtained in both studied conditions. Samples were then mixed with TEOS, dried, and heated at 450°C to ensure the PSB removal from the silica matrix. TEM and SEM results clearly show that final silica pore size is within the same order of magnitude than initial PSB. Finally, platinum decorated silica matrix with chosen pore sizes was successfully prepared.

International audience; The isotope effects in the sonoluminescence spectra of light and heavy water under ultrasound indicate the formation of a non‐equilibrium plasma inside the collapsing cavitation bubbles. The picture demonstrates the active cavitation zones in water at 204 kHz.

In this paper, we report a detailed characterisation of chromium doped iron oxide catalysts using a range of techniques to establish the nature of chromium species in the near surface and bulk of iron oxide, high-temperature shift (HTS) catalysts. In particular we have employed X-ray absorption spectroscopy Cr K-edge near edge and extended fine structure data for comparison with chemical and X-ray photoelectron spectroscopy. There was excellent agreement between the techniques in terms of identification and quantification of Cr(6+) and Cr(3+) species as a function of calcination temperatures between 100 and 500 °C.

The speciation and structural evolution of nanoscale yttrium-enriched oxides in numerous reduced activation oxide dispersion strengthened (ODS) ferritic steels have been investigated by X-ray absorption fine structure (XAFS) spectroscopy (including X-ray absorption near-edge structure and extended X-ray absorption fine structure) and transmission electron microscopy (TEM). The local structure and speciation of Y-enriched oxides during the fabrication process have been traced by Yttrium (Y) K-edge XAFS in fluorescence mode for both mechanical alloyed (MA) powders and compacted ODS alloys. After 24 h of milling, only 10%–14% of the initially added 0.3 wt. % Y 2 O 3 dissolves into the steel matrix and titanium (Ti) exhibits a minor influence on the Y solid solution during the MA. The EXAFS analysis for compacted ODS alloys indicates the formation of new Y-enriched oxides rather than initial Y 2 O 3 . The presence of Y–Cr–O/Y 2 O 3 has been confirmed by EXAFS and energy dispersed X-ray spectroscopy (EDX) elemental mapping in the compacted ODS alloy without Ti, while Y–Ti–O/Y 2 O 3 was observed in Ti-containing (0.2–0.4 wt. %) ODS alloys. The addition of Ti exhibits an evident influence on the consolidation process rather than in the MA.

The effects of exposure to a monochromatic 10 keV X-ray beam on thermally induced crystallization of lithium disilicate glass have been investigated and rendered two unexpected findings. First, it was found that an extended exposure during the nucleation heat treatment increased the number of nucleation sites. Second, it was observed that the effects extended far beyond the sample region that was directly exposed to the X-ray beam. The effects were confined to the direction perpendicular to the polarization of the synchrotron radiation beam that was used. The effects could be attributed to photo electrons created not only by the direct X-ray beam but also by the scattered radiation. Further evidence of the influence of photo electrons due to scattered X-rays is found in the results of an online crystallization study on a lysozyme solution.

The redox behaviour of a CuO–CeO2/Al2O3 catalyst is studied under propane reduction and re-oxidation. The evolution of the local Cu and Ce structure is studied with in-situ transmission X-ray absorption spectroscopy (XAS) at the Cu K and Ce L3 absorption edges. CuO and CeO2 structures are present in the catalyst as such. No structural effect on the local Cu structure is observed upon heating in He up to 873 K or after pre-oxidation at 423 K. Exposure to propane at reaction temperature (600–763 K) fully reduces the Cu2+ cations towards metallic Cu0. Quick EXAFS spectra taken during reduction show a small amount of intermediate Cu1+ species. Parallel to the CuO reduction, CeO2 is also reduced in the same temperature range. About 25% of the Ce4+ reduces rapidly to Ce3+ in the 610–640 K temperature interval, while beyond 640 K a further slower reduction of Ce4+ to Ce3+ occurs. At 763 K, Ce reduction is still incomplete with 32% of Ce3+. Re-oxidation of Cu and Ce is fast and brings back the original oxides. The propane reduction of the CuO–CeO2/Al2O3 catalyst involves both CuO and CeO2 reduction at similar temperatures, which is ascribed to an interaction between the two compounds.

The structural properties of three Fe-based Fischer–Tropsch synthesis (FTS) catalysts containing different amounts of Cu, K and SiO2 additives were investigated during pretreatment and FTS in a fixed bed-like reactor using combined in situ X-ray absorption fine structure (XAFS)/wide angle X-ray scattering (WAXS) techniques. This combination enabled acquisition of complementary information regarding the local environment of iron atoms from XAFS and crystalline phases from WAXS during H2 and CO/H2 pretreatment and FTS at 1 bar. The presence of the SiO2 support and promoter elements significantly influenced the structural properties of the catalysts after pretreatment. After FTS, H2 pretreated catalysts mainly consisted of amorphous θ-Fe3C clusters (unsupported catalysts) or amorphous iron (II) silicate (supported catalyst), while the CO/H2 pretreated catalysts all consisted mainly of γ-Fe and χ-Fe5C2. Catalysts activated in CO/H2 showed superior stability and activity, while H2 pretreated unsupported catalysts deactivated rapidly during the first 15 h of FTS.

The dissolution process of metal complexes in ionic liquids was investigated by a multiple-technique approach to reveal the solvate species of the metal in solution. The task-specific ionic liquid betainium bis(trifluoromethylsulfonyl)imide ([Hbet][Tf(2)N]) is able to dissolve stoichiometric amounts of the oxides of the rare-earth elements. The crystal structures of the compounds [Eu(2)(bet)(8)(H(2)O)(4)][Tf(2)N](6), [Eu(2)(bet)(8)(H(2)O)(2)][Tf(2)N](6) x 2 H(2)O, and [Y(2)(bet)(6)(H(2)O)(4)][Tf(2)N](6) were found to consist of dimers. These rare-earth complexes are well soluble in the ionic liquids [Hbet][Tf(2)N] and [C(4)mim][Tf(2)N] (C(4)mim = 1-butyl-3-methylimidazolium). The speciation of the metal complexes after dissolution in these ionic liquids was investigated by luminescence spectroscopy, (1)H, (13)C, and (89)Y NMR spectroscopy, and by the synchrotron techniques EXAFS (extended X-ray absorption fine structure) and HEXS (high-energy X-ray scattering). The combination of these complementary analytical techniques reveals that the cationic dimers decompose into monomers after dissolution of the complexes in the ionic liquids. Deeper insight into the solution processes of metal compounds is desirable for applications of ionic liquids in the field of electrochemistry, catalysis, and materials chemistry.

Visible/NIR spectrophotometry, solid-state NMR and spectroscopy reveal the hydrolysis of the PF6− anion in the room-temperature ionic liquid [BuMeIm]PF6, where BuMeIm+ is 1-butyl-3-methylimidazolium, in the presence of water and AnCl62−, where An(IV) is Th(IV), Np(IV), and Pu(IV). Slow absorption spectra evolution of AnCl62− solutions is finished by solid products' precipitation. Solids are attributed to the mixture of An(IV) phosphates and fluorophosphates.

This review summarizes recent studies of multibubble sonoluminescence (MBSL) in aqueous media in order to highlight new insights into the origin of the sonochemical activity. The observation of OH(C2Σ+-A2Σ+) emission band and a spectroscopic analysis of OH(A2Σ+-X2Πi) emission band in MBSL of water pre-equilibrated with noble gases revealed the formation of a nonequilibrium plasma inside the collapsing bubble (Te>Tv>Tr, where Te is an electron temperature, Tv is a vibrational temperature and Tr is a rotational (gas) temperature). The Te and Tv estimated using OH(A2Σ+-X2Πi) emission band increase with ultrasonic frequency. In Xe the Tv of OH(A2Σ+) state is much higher than in Ar most probably due to the lower ionization potential of Xe. The MBSL of C2∗ Swan band (d3Πg-a3Πu) measured in aqueous tert-butanol (t-BuOH) solutions correlates with the data obtained for OH(A2Σ+-X2Πi) emission band. Analysis of the gaseous products of t-BuOH sonolysis revealed a significant sonochemical activity even at high t-BuOH concentration when MBSL is totally quenched, indicating that drastic intrabubble conditions (plasma) are not necessarily accompanied by sonoluminescence. The nonequilibrium plasma model of cavitation allows to explain the reverse carbon isotope effect observed during the sonolysis of water in the presence of Ar/CO gas mixture.

A technique based on pulsed ultrasound and sonoluminescence emission was used to measure the size and size distribution of bubbles generated by 355 kHz power ultrasound under continuous Ar or He flow in aqueous NaCl solutions. It was observed that the bubble size strongly decreased with increasing NaCl concentration and that this decrease was much stronger than in solutions presaturated with Ar or He. This size decrease is attributed to the combination of the salting-out effect of the salt and the introduction of bubble nuclei by the continuous gas flow. Besides, the comparison of Ar and He bubbles underlines the effect of the gas diffusion coefficient on the bubble size reached.

Kinetics of hydrogen formation was explored as a new chemical dosimeter allowing probing the sonochemical activity of argon-saturated water in the presence of micro- and nano-sized metal oxide particles exhibiting catalytic properties (ThO2, ZrO2, and TiO2). It was shown that the conventional sonochemical dosimeter based on H2O2 formation is hardly applicable in such systems due to catalytic degradation of H2O2 at oxide surface. The study of H2 generation revealed that at low-frequency ultrasound (20 kHz) the sonochemical water splitting is greatly improved for all studied metal oxides. The highest efficiency is observed for relatively large micrometric particles of ThO2 which is assigned to ultrasonically-driven particle fragmentation accompanied by mechanochemical water molecule splitting. The nanosized metal oxides do not exhibit particle size reduction under ultrasonic treatment but nevertheless yield higher quantities of H2. The enhancement of sonochemical water splitting in this case is most probably resulting from better bubble nucleation in heterogeneous systems. At high-frequency ultrasound (362 kHz), the effect of metal oxide particles results in a combination of nucleation and ultrasound attenuation. In contrast to 20 kHz, micrometric particles slowdown the sonolysis of water at 362 kHz due to stronger attenuation of ultrasonic waves while smaller particles show a relatively weak and various directional effects.

A UV/vis/near-IR spectroscopic study shows that in [BuMeIm][(CF3SO2)2N] hydrophobic room-temperature ionic liquid solutions, [BuMeIm]2[AnCl6] complexes, where BuMeIm+ is 1-n-butyl-3-methylimidazolium and An(IV) is Np(IV) or Pu(IV), have an octahedral An(IV) environment similar to that observed in solid complexes. Water has no influence on the absorption spectra of AnCl6(2-) complexes, indicating their stability to hydrolysis in ionic liquid. Adding [BuMeIm]Cl modifies the UV/vis/near-IR absorption spectra of An(IV) in the ionic liquid and causes solids to precipitate. The solid-state reflectance spectra of the precipitates reveal considerable differences from the corresponding An(IV) hexachloro complexes. A voltammetric study indicates that AnCl6(2-) complexes are electrochemically inert in [BuMeIm][(CF3SO2)2N] at the glassy carbon working electrode. By contrast, quasi-reversible electrochemical reduction An(IV)/An(III) and An(IV) oxidation are observed in ionic liquids in the presence of [BuMeIm]Cl. The oxidation wave of noncoordinated chloride ions interferes with the An(IV) oxidation waves. The spectroscopic and voltammetric data clearly indicate the formation of nonoctahedral actinide(IV) chloride complexes with a Cl-/An(IV) ratio exceeding 6/1 in [BuMeIm][(CF3SO2)2N] in excess chloride ions.

The compositional structure of high density arrays of coaxial nanocables, consisting of germanium nanowires surrounded by cobalt nanotube sheaths, within anodic aluminium oxide membranes, were investigated by various X-ray analysis techniques. The nanocable arrays were prepared using a supercritical fluid inclusion process, whereby the cobalt nanotube precursor was first deposited on the pore walls of the nanoporous membranes and subsequently filled with germanium to form coaxial nanocables. The composition and structure of both the as-synthesised (450 °C) and annealed (850 °C) nanostructures were investigated by X-ray diffraction at high angles (XRD), X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge spectroscopy (XANES).

The behavior of U(IV) octahedral complexes [cation]2[UCl6], where the [cation]+ is [BuMeIm]+ and [MeBu3N]+, is studied using UV/visible spectroscopy, cyclic staircase voltammetry, and rotating disk electrode voltammetry in hydrophobic room-temperature ionic liquids (RTILs) [BuMeIm][Tf2N] and [MeBu3N][Tf2N], where BuMeIm+ and MeBu3N+ are 1-butyl-3-methylimidazolium and tri-n-butylmethylammonium cations, respectively, and Tf2N- is the bis(trifluoromethylsulfonyl)imide anion. The absorption spectra of [cation]2[UCl6] complexes in the RTIL solutions are similar to the diffuse solid-state reflectance spectra of the corresponding solid species, indicating that the octahedral complex UCl6(2-) is the predominant chemical form of U(IV) in Tf2N--based hydrophobic ionic liquids. Hexachloro complexes of U(IV) are stable to hydrolysis in the studied RTILs. Voltammograms of UCl(6)2- at the glassy carbon electrode in both RTILs and at the potential range of -2.5 to +1.0 V versus Ag/Ag(I) reveal the following electrochemical couples: UCl6-/UCl6(2-) (quasi-reversible system), UCl(6)2-/UCl6(3-) (quasi-reversible system), and UCl(6)2-/UCl6(Tf2N)x-3+x (irreversible reduction). The voltammetric half-wave potential, Ep/2, of the U(V)/U(IV) couple in [BuMeIm][Tf2N] is positively shifted by 80 mV compared with that in [MeBu3N][Tf2N]. The positive shift in the Ep/2 value for the quasi-reversible U(IV)/U(III) couple is much greater (250 mV) in [BuMeIm][Tf2N]. Presumably, the potential shift is due to the specific interaction of BuMeIm+ with the uranium-hexachloro complex in ionic liquid. Scanning the negative potential to -3.5 V in [MeBu3N][Tf2N] solutions of UCl6(2-) reveals the presence of an irreversible cathodic process at the peak potential equal to -3.12 V (at 100 mV/s and 60 degrees C), which could be attributed to the reduction of U(III) to U(0).

Ultrasonic irradiation with the frequency of 20–22 kHz and absorbed acoustic power about 0.4 W ml–1 causes degradation of An(IV) tetrakis-β-diketonates, AnL4, where An(IV) is Th(IV), Np(IV), and Pu(IV), and HL is hexafluoroacetylacetone (HFAA) and dibenzoylmethane (HDBM), in hexadecane solutions in the presence of argon. The rate of the sonochemical process corresponds to a first-order kinetic law with respect to metal β-diketonate concentrations. The first-order rate constant of sonolysis increases with the increase in the volatility of the metal complexes. Solid sonication products consisted of a mixture of actinide carbides and partial degradation products, PDP, of initial metal β-diketonates. It is assumed that metal carbides are formed within the cavitating bubbles as a result of high-temperature process with participation of actinide(IV) β-diketonates and solvent vapours. PDP formation is attributed to the thermolysis of the complexes in a liquid reaction zone surrounding the cavitating bubble. To cite this article: S.I. Nikitenko et al., C. R. Chimie 7 (2004).

We report here a novel method of catalytic transformation of amorphous carbon to CNT. The method involves Fe(CO)5 thermolysis in the presence of carbon black at high pressure. A mechanism is proposed; it is verified by solid-state NMR measurements.

Amorphous tungsten oxide has been prepared by ultrasound irradiation of a solution of tungsten hexacarbonyl W(CO)6 in diphenylmethane (DPhM) in the presence of an Ar (80%)–O2 (20%) gaseous mixture at 90 °C. Heating this amorphous powder at 550 °C under Ar yields snowflake-like dendritic particles consisting of a mixture of monoclinic and orthorhombic WO2 crystals. Annealing of the as-prepared product in Ar at 1000 °C causes the formation of a WO2–WO3 mixture containing nanorods (around 50 nm in diameter) and packs of these nanorods. Heating the product in air for 3 hours leads to triclinic WO3 crystal formation, with a basic size of 50–70 nm. The prepared oxides have been characterized by elemental analysis, X-ray powder diffraction measurements, FTIR spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDX).

International audience; The autocatalytic sonochemical reaction of Fe(CO)5 decomposition in [BuMeIm][Tf2N] provides iron nanoparticles in higher yields than in tetralin. Such a difference is explained by the higher decomposition of the intermediate Fe3(CO)12 according to the two-sites model of the sonochemical reactions and the specific properties of the ionic liquid.

International audience; The chemical and physical effects of ultrasound 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 and to the emission of light, named sonoluminescence. In this manuscript, we describe the techniques allowing study of extreme intrabubble conditions and chemical reactivity of acoustic cavitation in solutions. The analysis of sonoluminescence spectra of water sparged with noble gases provides evidence for nonequilibrium plasma formation. The photons and the "hot" particles generated by cavitation bubbles enable to excite the non-volatile species in solutions increasing their chemical reactivity. For example the mechanism of ultrabright sonoluminescence of uranyl ions in acidic solutions varies with uranium concentration : sonophotoluminescence dominates in diluted solutions, and collisional excitation contributes at higher uranium concentration. Secondary sonochemical products may arise from chemically active species that are formed inside the bubble, but then diffuse into the liquid phase and react with solution precursors to form a variety of products. For instance, the sonochemical reduction of Pt(IV) in pure water provides an innovative synthetic route for monodispersed nanoparticles of metallic platinum without any templates or capping agents. Many studies reveal the advantages of ultrasound to activate the divided solids. In general, the mechanical effects of ultrasound strongly contribute in heterogeneous systems in addition to chemical effects. In particular, the sonolysis of PuO 2 powder in pure water yields stable colloids of plutonium due to both effects. Video Link The video component of this article can be found at