Sonolysis of metal beta-diketonates in alkanes

Sonochemical decomposition effects of nickelocene aiming for low-temperature and dispersant-free synthesis of nickel fine particle

Sonochemical decomposition effects of nickelocene, which sublimates easily were investigated to synthesize dispersant-free nickel fine particles at low temperature. In a hydrazine monohydrate and 2-propanol mixed solvent, the reduction of nickelocene was promoted by ultrasound irradiation, and nickel fine particles were synthesized while precluding the sublimation of nickelocene. Unlike the common hydrazine reduction of nickel salts, which requires multiple-step reactions, nickelocene was reduced directly without forming intermediates. The effect of the water-bath temperature (20-60 °C) was investigated, where larger fine particles were synthesized using a higher water-bath temperature (60 °C). When irradiated at 20 °C, the reduction rate of nickelocene was low, leading to the formation of nickel fine particles and organic nanoparticles via the reduction and decomposition of nickelocene. The ultrasound frequency was also investigated, where fine nickel particles were synthesized using low-frequency ultrasound irradiation. The formation of high-temperature hotspots led to the diffusion and growth of nickel on the surface of the nickel fine particles; therefore, raspberry-like nickel fine particles were synthesized. In this study, the difficult-to-handle nature of nickelocene, owing to its sublimation properties, was easily overcome by ultrasound irradiation. Instantaneous and localized reactions at hotspots contributed to inhibiting particle growth. Furthermore, Ni fine particles were synthesized via a direct reduction pathway, which differs from previous reactions. This method represents a new, dispersant-free, low-temperature process for synthesizing Ni fine particles.

Sonochemistry of actinides: from ions to nanoparticles and beyond

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.

Mechanism study of Single-Step synthesis of Fe(core)@Pt(shell) nanoparticles by sonochemistry

Transition metal (TM) core-platinum (Pt) shell nanoparticles (TM@Pt NPs) are attracting a great deal of attention as highly active and durable oxygen reduction reaction (ORR) electrocatalysts of fuel cells and metal-air batteries. However, most of the reported synthesis methods of TM@Pt NPs are multistep in nature, a significant disadvantage for real applications. In this regard, our group has reported a single-step method to synthesize TM@Pt NPs for TM = Mn, Fe, Co, and Ni by using sonochemistry, namely the UPS (ultrasound-assisted polyol synthesis) method. Previously, we proposed the mechanism of the formation of these TM@Pt NPs by UPS method, but rather in a rough sense. Some details are missing and the optimal conditions have not been established. In the present work, we performed detailed studies on the formation mechanism of UPS reaction by using Fe@Pt NPs as the model system. Effects of synthesis parameters such as the nature of metal precursor, conditions of ultrasound, and temperature profile as a function of reaction time were assessed, along with the analyses of intermediates during the UPS reaction. As results, we verified our previously proposed mechanism that, under appropriate conditions, Fe core is formed through the cavitation and implosion of the solvent, induced by the ultrasound, and the Pt shell is formed by the chemical reaction between Fe core and Pt reagent, independent from the direct effect of ultrasound. In addition, we established the optimal conditions to obtain a high purity Fe@Pt NPs in a high yield (>90% based on Pt), which may enable the increase of synthesis scale of Fe@Pt NPs, a necessary step for the real application of TM@Pt NPs.

Sonochemical precipitation of amorphous uranium phosphates from trialkyl phosphate solutions and their thermal conversion to UP2O7

Insoluble amorphous precipitates containing uranyl and phosphate ions are obtained by sonication of solutions of three uranyl precursors, UO2(X)2, X=NO3, CH3COO, CH3C(O)CHC(O)CH3 (acetylacetonate, acac), in triesters of phosphoric acid, OP(OR)3, R=Me (trimethyl phosphate, TMP), Et (triethyl phosphate, TEP). TMP and TEP are used as high-boiling solvents and they serve also as a source of phosphate anions. Sonolysis experiments were carried out under flow of Ar at 40°C on a Sonics and Materials VXC 500W system (f=20 kHz, Pac=0.49 W cm(-3)). Powder X-ray diffraction (PXRD) reveals amorphous character of all obtained precipitates. The presence of uranyl and phosphate is evidenced by IR spectroscopy and ICP-OES analysis reveals the content of both U (38.6-43.4 wt%) and P (11.0-13.6 wt%). The thermal behavior of the substances was studied by TG/DSC analysis, which shows weight losses in the range of 19.21-24.08%. On heating the amorphous precipitates to 1000°C, crystalline uranium diphosphate UP2O7 is obtained in all cases as the only crystalline phase. Uranyl(VI) is reduced during thermolysis to U(IV) as there is no characteristic vibration of UO2(2+) in the IR spectra of solid UP2O7 products. The ICP-OES analysis of U and P content in precipitates allowed us to calculate the efficiency of precipitation of uranium from mother liquor and to compare it with the efficiency calculated from the data received by the PXRD and TG/DSC analyses. The efficiency of the uranium removal attained by our sonoprecipitation procedure was typically 30-35%. These sonochemical precipitation reactions providing insoluble uranium phosphates may be potentially interesting models for the description of behavior of uranium-containing waste or reprocessing streams.

Sonochemical synthesis of amorphous nanoscopic iron(III) oxide from Fe(acac)3

Amorphous nanoscopic iron(III) oxide with interesting magnetic properties was prepared by sonolysis of Fe(acac)(3) under Ar in tetraglyme with a small amount of added water. The organics content and the surface area of the Fe(2)O(3) nanoparticles can be controlled with an amount of water in the reaction mixture and it increases from 48 m(2)g(-1) for dry solvent up to 260 m(2)g(-1) when wet Ar is employed. For further monitoring of the particle size and morphology and for the study of the surface, magnetic and thermal properties, the sample with 2 vol.% of H(2)O was chosen. SEM showed nanoscopic composite particles of a uniform size distribution and nearly spherical shapes with an estimated diameter of 20 nm. Such composites are built from amorphous iron(III) oxide nanoparticles (3 nm) embedded in an acetate matrix as proved by TEM and IR spectroscopy. Temperature-dependent Mössbauer spectra demonstrate a very narrow magnetic transition with an unusually low transition temperature around 25K reflecting the system of magnetically non-interacting ultrasmall particles with a narrow size distribution. The in-field (5T) Mössbauer spectrum recorded at 5K shows a minimum change compared to the zero-field spectrum indicating an absence of the long-range magnetic ordering. The composite particles are thermally stable up to 150 degrees C, which is confirmed by DSC, TG, and by the constant surface area. At higher temperatures, acetate groups are removed from the particle surface, which is documented by the increased surface area and disappearance of their IR bands.

A remote valency control technique: catalytic reduction of uranium(vi) to uranium(iv) by external ultrasound irradiation

We here report the enhancement of a sonochemical effect (chemical reaction induced by ultrasound irradiation) by a Pt black catalyst; the sonochemical reduction of the highly stable U(VI) was demonstrated using this catalytic reaction.

High-frequency acoustic emissions generated by a 20 kHz sonochemical horn processor detected using a novel broadband acoustic sensor: a preliminary study

This paper describes the application of a novel broadband acoustic sensor to evaluating the acoustic emissions from cavitation produced by a typical commercial 20 kHz sonochemical horn processor. Investigations of the reproducibility of the processor, and of the variation in cavitation emissions as a function of output setting and sensor location are described, and resulting trends discussed in terms of the broadband integrated power in the megahertz frequency range. Companion studies with a conventional membrane hydrophone have illustrated for the first time that cavitation emissions produced by a sonochemical horn processor can extend to frequencies beyond 20 MHz, and the sensor shows that significant nonlinearity can be seen in measured cavitation activity with increasing nominal output power.