This study reports the synthesis of a Ti@TiO2/Ni nanocomposite containing 20 wt% Ni via sonohydrothermal treatment combined with ultrasonic reduction of Ni2+ using hydrazine. The composite exhibited notable photothermal activity toward hydrogen production in glycerol solution, achieving a rate of 4.41 mmol h−1 g−1 at 94 °C, which is 5.5 times higher than bare TiO2 with an activation energy of 22 ± 1.5 kJ mol−1. Interestingly, methane (CH4) formation was observed exclusively in the Ni-containing composite, attributed to a Ni-catalyzed methanation pathway. Photoelectrochemical measurements revealed that Ni incorporation does not enhance the photocurrent response, suggesting that the improved performance arises primarily from surface catalytic effects and thermally-assisted reaction pathways rather than enhanced charge separation. These findings demonstrate that Ni modifies the reaction pathway of Ti@TiO2, enabling dual H2 and CH4 production.

Hydrothermal (HT) treatment of nitinol nanoalloy (NiTi) in pure water provides a simple and environmentally friendly route for the synthesis of NiTi@TiO2/Ni core-shell nanoparticles (NPs) that are efficient for CO2 methanation. The incongruent oxidation of pristine NiTi NPs results in the formation of anatase TiO2 and metallic Ni nanocrystals on the surface of the NiTi core. The TiO2 and Ni contents increase with increasing the HT treatment temperature in the range of 160–200 °C. The resulting NiTi@TiO2/Ni particles are ferromagnetic, and their saturation magnetization increases with metallic nickel content. Unlike pristine NiTi nanoparticles, NiTi@TiO2/Ni NPs exhibit light-assisted thermal catalytic activity. Careful selection of HT conditions enables the elaboration of a NiTi@TiO2/Ni catalyst with superior activity for CO2 methanation and pronounced photo-enhancement of the reaction rate. Upon exposure to 365 nm light, the apparent activation energy decreases by approximately 20 kJ·mol−1, suggesting the dominant contribution of an electron-driven photo-enhancement into the overall reaction compared to thermalization mechanism. The selectivity of CO2 methanation was found to be close to 100% over the temperature range of 160–260 °C.

While bulk PuO2 is known to be strongly resistant to dissolution, even under ultrasonic irradiation, this study demonstrates that nanometric PuO2 samples can exhibit enhanced reactivity when sonicated under an Ar/(20 %)O2 atmosphere. Sonication of powdered PuO2 nanoparticles (∼5 nm) in pure water was found to be ineffective. In contrast, colloidal PuO2 nanoparticles (∼3 nm) prepared via hydrolysis exhibited markedly different behavior, leading to the accumulation of Pu(VI), with sonochemically-generated H2O2 playing a crucial role in the process. Further investigations identified an intermediate species implicated in the dissolution process, agreeing with a recently described Pu(IV) peroxide compound. Despite the chemical similarity of the PuO2 nanoparticles, this study highlights their dual reactivity under conditions favoring H2O2 formation highlighting an important role of the material's preparation method. Beyond underscoring the critical role of H2O2 in the reactivity of PuO2 nanoparticles, this study also evidences a potential pathway for their transformation under environmental conditions where radiolysis can generate similar chemical environments.

While recent studies have provided a wealth of information about the structure of oxide nanoparticles resulting from Pu(IV) hydrolysis, little is known about their formation mechanism. This article describes the stabilization and characterization of a reaction intermediate observed during the formation of PuO2 colloidal nanoparticles in aqueous solution. The intermediate was captured by a kinetic blocking of the started hydrolysis reaction by dilution of the reacting medium into DOTA (pH 3.5), glycine (pH 2.0), or acetic acid (pH 1.1) aqueous solutions. Such an approach stopped the hydrolysis and condensation processes by complexation and allowed for stabilization of hexameric polynuclear structures of Pu(IV) that were thoroughly characterized using laboratory and synchrotron techniques (UV-vis, small angle X-ray scattering, L3-edge X-ray absorption spectroscopy, and M4-edge high energy resolution fluorescence detected-X-ray absorption near edge structure). Beyond the new insight given about the contribution of the [Pu6O4(OH)4]12+ cluster during the aqueous formation of colloidal PuO2 nanoparticles in aqueous conditions, this study confirms the added value of synchrotron radiation for the characterization of very dilute and strongly radioactive nanostructures, paving the way for further research in the domain.

Green hydrogen is a pillar for achieving global decarbonization and the reduction of greenhouse gas emissions. Here, a new, nature-inspired process for green hydrogen production using virtually unlimited natural resources is reported. Olivine, the most abundant mineral in the Earth's upper mantle, is key to this process. It is found that 20 kHz ultrasound accelerates hydrogen production from olivine suspensions in seawater under near-ambient conditions by almost 3000 times compared to the hydrothermal process. Strong mechanical stirring does not lead to hydrogen evolution in the temperature range of 40-90 °C. The striking effect of ultrasound is attributed to acoustic cavitation, which provides depassivation of the olivine surface, fragmentation of olivine particles, and local transient heating caused by collapsing bubbles. In principle, ultrasonic activation of the olivine/seawater system enables on-demand hydrogen production.

Large number of chemical reactions can be described rigorously using classical thermodynamics and classical kinetics. However, there are an increasing number of examples of chemical reactions that deviate from "classical" behavior. Describing them requires considering quantum effects. The purpose of this review is to emphasize the importance of such "non-classical" reactions in sonochemistry. Quantum effects in sonochemistry are a direct consequence of the formation of nonequilibrium plasma inside collapsing bubbles. Spectroscopic studies of multibubble sonoluminescence revealed that intrabubble processes cannot be described by a single gas temperature. Rather, vibrational excitation and ionization must also be considered. Most clearly, quantum effects in sonochemistry, like those in "classical" chemistry, appeared for kinetic isotope effects, KIE. The anomalous H/D KIE during water sonolysis in the presence of noble gases can be understood in terms of electron quantum tunneling during the heterolytic splitting of a water molecule. In addition, the inverse 13C/12C KIE observed during water sonolysis in the presence of CO indicated a similarity with a non-equilibrium plasma generated by CO excitation in a gas phase. This KIE originated from the quantum vibration-vibration pumping mechanism. In the concluding part of the review, some perspective research directions are discussed.

Although hydrogen peroxide (H2O2) 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).

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. The conversion kinetics of the amorphous hydrogel to zeolite A and its further conversion to sodalite were studied. Syntheses were performed in the SHT reactor at 80 and 100 °C, varying the synthesis time from 15 minutes to several hours. The required time to obtain fully crystalline zeolite A under sonohydrothermal conditions was only 25 minutes, highlighting a significantly improved crystallization rate compared to silent conditions (a 9.6-fold kinetic gain). In addition, the resulting zeolite A has smaller particles and a more homogeneous particle size distribution than the zeolite synthesized by hydrothermal treatment. These results can be explained by the sonofragmentation of the amorphous gel and the concomitant enhanced mass transfer of the building units at the interface between the crystallite surface and the solution resulting from the acoustic cavitation activity under SHT conditions. Compared to classical hydrothermal heating, a drastic kinetic increase of the transformation of zeolite A into the more stable sodalite phase was also observed under sonohydrothermal conditions.

Development of efficient photothermal catalysts made of earth-abundant elements is of prime importance for heterogeneous photocatalysis driven by solar light. Herein, we report for the first time the synthesis of NiTi@TiO2/Ni core-shell-satellite nanoparticles from pristine nitinol nanopowder (NiTi) by simple and easily scalable ultrasonically assisted hydrothermal treatment in pure water (T = 200 C-degrees, P = 14 bar, f = 20 kHz, P-ac = 17 W, tau = 3 h). Prepared material exhibits unique set of properties, such as strong capability of light-to-heat conversion, good magnetization, high stability, and remarkable thermally assisted photocatalytic hydrogen production (5.5 mmol h(-1) g(-1) at T = 90 C-degrees). The core-shell-satellite morphology of NiTi@TiO2/Ni particles maximizes the contact area between the heat generating metallic core and photocatalytically active TiO2/Ni nanocrystalline shell providing the most efficient photothermal effect in the processes of H-2 production and CO2 methanation without CO emission. In addition, significant magnetic susceptibility of the NiTi@TiO2/Ni nanoparticles allows their easy recovery from solution with an external magnetic field. Noncongruent surface oxidation of nanoalloys reported in this work paves the way to the preparation of new generation of catalysts with advanced photothermal properties.

The dissolution of metals, influenced by mechanical and chemical factors, plays a crucial role in various applications. Ultrasonic irradiation has been explored for its ability to enhance dissolution rates and modify surface characteristics. In this study, we investigate the dissolution of magnesium (Mg) and magnesium alloys under high-intensity focused ultrasound (HIFU) conditions with frequency sweeping (wobbling). Our findings reveal distinct effects of cavitation and acoustic streaming on the dissolution process. For pure magnesium, ultrasonic treatment significantly increases dissolution rates compared to silent conditions. Negative frequency sweeps result in the highest dissolution rates, linked to increased cavitation activity, while positive sweeps reduce dissolution rates but maintain acoustic streaming effects. The removal of surface oxides is accelerated in all sonication conditions. Macro- and micro-roughness patterns on the surface correspond to the wobbling frequency range, with wavelengths matching the average ultrasonic frequency. However, dissolution is not uniform across the sample, and preferential attack occurs at the focal point during negative frequency sweeps. In contrast, magnesium alloys exhibit lower dissolution rates than pure Mg. The alloy's mechanical properties make it less susceptible to cavitation erosion but more sensitive to acoustic streaming-induced dissolution. Grain boundaries are preferentially attacked, revealing differences between ductile pure Mg and the harder, more cavitation-resistant, alloy. This study highlights the complex interplay between cavitation and acoustic streaming in the dissolution of magnesium and its alloys under HIFU conditions, shedding light on the limits and potential applications of this technique, particularly in microstructure analysis.

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 UO2 was investigated in dilute aqueous solutions saturated with Ar/(20 %)O2 (20 °C). Optimized parameter settings enabled the complete conversion of UO2 micrometric platelets into uranyl peroxide precipitates, referred to as (meta-)studtite [(UO2(O2)(H2O)2)xH2O] with x = 2 or 4. While the most acidic conditions yielded elongated crystal shapes in agreement with a dissolution/reprecipitation mechanism, softer conditions allowed the pseudomorphic transformation of the platelet shape oxide suggesting a complex formation mechanism. For specific conditions, this unprecedented morphology was accompanied with the formation of a hole in the platelet center. Investigations revealed that the formation of the drilled polymorphs is related to a perfect blend of H+, in-situ generation of H2O2 and high-frequency ultrasound, and is most probably related to the sono-capillary effect. These insights pave the way for new sonochemical approaches dedicated to the preparation of material polymorphs tailoring specific structural properties.

This Editorial refers to the Special Issue entitled “Photocatalysis and Sonocatalysis for Environmental Applications: Synergy or Competition [...]

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, UO2+x NPs were successfully prepared by sonochemistry from U(IV) solutions previously stabilised in a hydrochloric medium (20 kHz, 65 °C, Ar/(10%)CO). Colloidal suspensions were found to be composed of crystalline and spherical NPs showing a UO2-like structure and measuring 18.0 ± 0.1 nm (SAXS, HR-TEM and PXRD techniques). In comparison with the controlled hydrolysis approach used as a reference, sonochemistry appears to be a simple and original synthesis route providing larger, better defined and more crystalline UO2+x NPs with a narrower size distribution. These well-defined NPs offer new opportunities for the preparation of reference actinide materials devoted to fundamental, technological and environmental studies.

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.

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 αH = 14.6 ± 1.8 in a 10% H2O/D2O mixture under 20 kHz ultrasound. The anomalous H/D KIE is attributed to electron quantum tunneling in the plasma produced by cavitation. In addition, CO2 formed simultaneously with hydrogen during the sonochemical process is enriched with the 13C isotope, which indicates a V-V pumping mechanism typical for non-equilibrium plasma. Both observed KIEs unambiguously point to the contribution of quantum effects in sonochemical mechanisms.

Large H/D isotope separation coefficient and its variation with temperature indicates a hole-mediated O–H bond cleavage as the limiting stage of photothermal hydrogen production.

The study of the formation of radiolytic products, such as molecular hydrogen and nitrous acid, is of primary importance in the reprocessing of spent nuclear fuel and the storage of aqueous solutions containing radioactive materials. The radiolytic yields of molecular hydrogen, nitrous acid and nitrous oxide from alpha radiolysis of nitric acid solutions containing plutonium have been experimentally investigated. The results have shown that the yields of radiolytic products depends on the nitric acid concentration as well as the oxidation state of plutonium. However, the influence of plutonium oxidation state on radiolytic yields is less notable as the nitric acid concentration increases. Molecular hydrogen production decreases with increasing nitric acid concentration while nitrous acid and nitrous oxide productions increase. While radiolytic yields from plutonium(IV) nitric acid solutions have been previously investigated, this study provides radiolytic yields from alpha radiolysis of plutonium(III) and plutonium(VI) nitric acid solutions for molecular hydrogen, nitrous acid and nitrous oxide. These information provide insight into the role played by plutonium redox behaviour on the formation of radiolytic products.