Sonohydrothermal synthesis of zeolite A and its phase transformation into sodalite.

The sonohydrothermal (SHT) treatment is an innovative technique allowing the simultaneous coupling of low frequency ultrasound and hydrothermal conditions for the synthesis of materials. The aim of the present work was to investigate, for the first time, the synthesis of zeolite A and its formation mechanism under SHT conditions. The zeolite synthesis was carried out under sonohydrothermal conditions using a specially designed reactor that allows the application of ultrasonic irradiation at 20 kHz in an autoclave-type reactor heated up to 200 °C under autogenous pressure.

Micrometric drilling of (meta-)studtite square platelets formed by pseudomorphic conversion of UO under high-frequency ultrasound.

Pseudomorphic transformations are related to chemical conversions of materials while conserving their shape and structural features. Structuring ceramic shapes this way can be used to tailor the physico-chemical properties of materials that can benefit particular applications. In the context of spent nuclear fuel storage interacting with radiolysis products, the sonochemical behavior of powdered UO was investigated in dilute aqueous solutions saturated with Ar/(20 %)O (20 °C).

Sonochemically-Induced Reduction of Alkenes to Alkanes with Ammonia.

With the progressive defossilization of our industry, hydrogen (H ) has been identified as a central molecule to store renewable electricity. In this context, ammonia (NH ) is now rapidly emerging as a promising hydrogen carrier for the future. This game change indirectly impacts the field of fine chemistry where hydrogenation reactions are widely deployed.

Simultaneous H/D and C/C Anomalous Kinetic Isotope Effects during the Sonolysis of Water in the Presence of Carbon Monoxide.

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.

Conversion of Ammonia to Hydrazine Induced by High-Frequency Ultrasound.

Hydrazine is a chemical of utmost importance in our society, either for organic synthesis or energy use. The direct conversion of NH to hydrazine is highly appealing, but it remains a very difficult task because the degradation of hydrazine is thermodynamically more feasible than the cleavage of the N-H bond of NH . As a result, any catalyst capable of activating NH will thus unavoidably decompose N H .

Sonocatalytic degradation of EDTA in the presence of Ti and Ti@TiO nanoparticles.

The sonocatalytic degradation of EDTA (C = 5 10 M) in aqueous solutions was studied under 345 kHz (P = 0.25 W mL) ultrasound at 22-51 °C, Ar/20%O, Ar or air, and in the presence of metallic titanium (Ti) or core-shell Ti@TiO nanoparticles (NPs). Ti@TiO NPs have been obtained using simultaneous action of hydrothermal conditions (100-214 °C, autogenic pressure P = 1.

Physical and chemical characterization of shock-induced cavitation.

A strong impact on a water surface induces a shock wave propagation with a significant pressure variation leading to cavitation bubble formation. A new shock induced cavitation reactor described in this work was characterized by physical and chemical techniques. Water hammer model verification with Joukowsky approach allowed to determine the wave speed propagation and gas fraction in water submitted to shock.

Selective radical depolymerization of cellulose to glucose induced by high frequency ultrasound.

The depolymerization of cellulose to glucose is a challenging reaction and often constitutes a scientific obstacle in the synthesis of downstream bio-based products. Here, we show that cellulose can be selectively depolymerized to glucose by ultrasonic irradiation in water at a high frequency (525 kHz). The concept of this work is based on the generation of H˙ and ˙OH radicals, formed by homolytic dissociation of water inside the cavitation bubbles, which induce the cleavage of the glycosidic bonds.

Hypothesis about electron quantum tunneling during sonochemical splitting of water molecule.

Quantum tunneling in chemistry is often attributed to the processes at low or near room temperatures when the rate of thermal reactions becomes far less than the rate of quantum tunneling. However, in some rapid processes, quantum tunneling can be observed even at high temperatures. Herein, we report the experimental evidence for anomalous H/D kinetic isotope effect (KIE) during sonochemical dissociation of water molecule driven by 20 kHz power ultrasound measured in HO/DO mixtures saturated with Ar or Xe.

Insights into the sonochemical synthesis and properties of salt-free intrinsic plutonium colloids.

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 suspensions in pure water is reported. Kinetics showed that both chemical and mechanical effects of ultrasound contribute to the mechanism of Pu colloid formation.

Ultrasound-assisted reductive dissolution of CeO2 and PuO2 in the presence of Ti particles.

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.

Sonochemical water splitting in the presence of powdered metal oxides.

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.

Effect of operational conditions on sonoluminescence and kinetics of H2O2 formation during the sonolysis of water in the presence of Ar/O2 gas mixture.

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.

Influence of ultrasonic frequency on Swan band sonoluminescence and sonochemical activity in aqueous tert-butyl alcohol solutions.

The multibubble sonoluminescence (MBSL) spectra of t-BuOH aqueous solutions submitted to power ultrasound at 20, 204, 362, and 613 kHz show emissions for the Δυ = -1 to Δυ = +2 vibrational sequences of C2* Swan system (d(3)Πg → a(3)Πu). The Δυ=+2 emission overlaps with the CH(A-X) emission band. The maximal Swan band emission is observed when the MBSL of water itself is almost completely quenched.

Activating molecules, ions, and solid particles with acoustic cavitation.

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.

Thermal and sonochemical synthesis of porous (Ce,Zr)O2 mixed oxides from metal β-diketonate precursors and their catalytic activity in wet air oxidation process of formic acid.

Porous (Ce0.5Zr0.5)O2 solid solutions were prepared by thermolysis (T=285 °C) or sonolysis (20 kHz, I=32 W cm(-2), Pac=0.

Sonochemical deposition of platinum nanoparticles on polymer beads and their transfer on the pore surface of a silica matrix.

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.

Mechanism of Pt(IV) sonochemical reduction in formic acid media and pure water.

Sonochemical synthesis of platinum nanoparticles (Pt NPs) in formic acid solutions and pure water was investigated using a 20 kHz ultrasonic irradiation. The obtained results gave new insights on the underneath Pt(IV)  reduction mechanism in formic acid media under argon and in pure water under Ar/CO atmosphere. It was shown that in pure water sonochemical reduction of platinum ions occurs by hydrogen issued from homolytic water molecule split.

Effect of ultrasonic frequency on the mechanism of formic acid sonolysis.

The kinetics and mechanism of formic acid sonochemical degradation were studied at ultrasonic frequencies of 20, 200, and 607 kHz under argon atmosphere. Total yield of HCOOH sonochemical degradation increases approximately 6-8-fold when the frequency increased from 20 to 200 or to 607 kHz. At low ultrasonic frequencies, HCOOH degradation has been attributed to oxidation with OH(•) radicals from water sonolysis and to the HCOOH decarboxylation occurring at the cavitation bubble-liquid interface.

First synthesis of uranyl aluminate nanoparticles.

This paper describes, for the first time, a simple method for the synthesis of uranyl aluminate (URAL) nanoparticles. URAL was prepared by U(VI) hydrolytic precipitation with ammonia at pH = 11 in the presence of mesoporous alumina MSU-X under 20 kHz of sonication followed by annealing of the obtained solids at 800 degrees C. TEM, XAFS, powder XRD, and (27)Al MAS NMR studies revealed that the speciation of uranium in this system strongly depends on uranium concentration.

Potential applications of sonochemistry in spent nuclear fuel reprocessing: a short review.

The industrial treatment of spent nuclear fuel is based upon a hydrometallurgical process in nitric acid medium. In order to minimize the volume of radioactive waste it seems interesting to generate the reactive species in situ in such solutions using ultrasonic irradiation without addition of salt-forming reagents. This review summarizes for the first time the versatile sonochemical processes with uranium, neptunium and plutonium in homogeneous nitric acid solutions and heterogeneous systems.

Sonochemical reactions with mesoporous alumina.

Herein, we report the sonochemical reactions with MSU-X mesoporous alumina (m-Al(2)O(3)) in aqueous solutions. Sonication (f=20 kHz, I=30 Wcm(-2), W(aq)=0.67 WmL(-1), T=36-38 degrees C, Ar) causes significant acceleration of m-Al(2)O(3) dissolution in the pH range of 4-11.