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 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).

The scavenging of OH(?) radicals formed during H(2)O sonolysis with nitrate-ions was studied in HNO(3)/NaNO(3) mixture at the constant NO(3)(-) ions concentration ([HNO(3)]+[NaNO(3)])=1 M in Ar atmosphere. Small amounts of N(2)H(5)NO(3) was added to solutions to avoid HNO(2) accumulation due to HNO(3) sonolysis. It was shown that the increase of [H(+)] causes the increase of H(2)O(2) formation rate (W(H(2)O(2)). (W(H(2)O(2)) values reach the plateau at [HNO(3)] approximately 1 M. The (W(H(2)O(2)) ratio in solution with [H(+)]=1 M and pure water was found to be equal to 2.4+/-0.4. It was assumed that (W(H(2)O(2)) increase in nitric acid medium is related to the changing of H(2)O(2) formation mechanism. In pure water H(2)O(2) is formed due to the OH(*) radicals recombination. In HNO(3)+NaNO(3) mixture the mechanism of H(2)O(2) formation consists in conversion of OH(*) radicals to NO(3)(*) radicals followed by NO(3)(*) radicals hydrolysis. Results obtained show that OH(*) radicals recombination mainly occurs in the liquid phase surrounding the cavitating bubble.

Air-stable Fe/Fe3C nanocrystalline particles have been prepared by sonicating Fe(CO)(5) in diphenylmethane solutions under argon and subsequently annealing the amorphous as-prepared product in an inert atmosphere. Changing the sonication conditions and annealing temperature allows control of the size of the particles, as well as their composition and magnetic properties. Material obtained under appropriate conditions possesses a high saturation magnetization close to that of bulk iron (M-s/M-o= 0.97-1.06) and good, soft magnetic properties (H-C = 0.50-0.05 A m(-1)). Nanocrystalline particles have a core-shell structure where a coating of Fe3C and carbon protects the body-centered cubic Fe in the core from oxidation.

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-beta-diketonates, AnL(4), 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 beta-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 beta-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) beta-diketonates and solvent vapours. PDP formation is attributed to the thermolysis of the complexes in a liquid reaction zone surrounding the cavitating bubble. (C) 2004 Academie des sciences. Published by Elsevier SAS. All rights reserved.

The kinetics of metal β-diketonates sonolysis was studied in hexadecane solutions using a UV/VIS spectrophotometric technique. The following complexes were prepared and studied: Cu(HFAA)2, Cu(DPM)2, Fe(ACAC)3, Ni(DPM)2, Er(DPM)3, Nd(DPM)3, Th(DPM)4, UO2(BTFA)2·TOPO, and Np(HFAA)4, where HHFAA is hexafluoroacetylacetone, HDPM is dipivaloylmethane, HACAC is acetylacetone, HBTFA is benzoyltrifluoroacetone, and TOPO is trioctylphosphine oxide. Sonolysis was performed under the following conditions: ultrasonic frequency 22 kHz, intensity of ultrasound 3–5 Wcm−2, temperature 70–92 °C, Ar atmosphere. The kinetic behavior of the studied complexes are interpreted using a two-site model of the sonochemical processes. In the case of metal β-diketonates with high vapor pressure the sonochemical reactions tend to occur in the gaseous phase of the cavitating bubbles. The sonolysis of less volatile complexes first occur in the liquid reaction zone surrounding the bubbles. Sonication of the studied complexes results in the formation of X-ray amorphous products consisted of a mixture of metal β-diketonates partial degradation products. Heating of as-prepared sonication products in air yields nanocrystalline oxides of corresponding metals.

Initial results on synthesis, magnetic properties and time stability of iron-iron carbide nanoparticles are presented. It is shown that as-prepared (after sonochemical synthesis in solution) material consists of small iron particles (d<10 nm) embedded in a polymeric matrix. It was found to be superparamagnetic. Consequent thermal annealing of as-prepared material at temperatures up to 1073 K in argon results, first, in the growth of the iron particles up to 150 nm. Second, the obtained powders become ferromagnetic. Third, such powders are air-stable due to the formation of an interfacial iron carbide layer during annealing. The air-stability of the iron-iron carbide powder was tested by time dependence measurements of its resistivity.

Sonolysis of diphenylmethane (DPhM) has been studied under the effect of 20 kHz ultrasound (absorbed acoustic power 0.45 W/ml, surface area of sonotrode 1 cm(2), volume of sonicated solution 100 ml) under argon at 60 degrees C. The solid product of the sonolysis was characterized by elemental analysis, FTIR, 13C MAS NMR, TGA/DSC, XRD and TEM techniques. It was found that the sonolysis of DPhM causes formation of the polymer with the composition similar to crosslinked polystyrene. Assumed mechanism of DPhM sonolysis consists of DPhM molecules dissociation inside the cavitating bubble. Secondary radical scavenging and radical recombination processes yields the sonopolymer in the liquid phase. The breakdown of the aromatic ring during DPhM sonolysis confirms that a very high temperature established in the cavitating bubble.

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.

Ultrasonic irradiation (22 kHz, Ar atmosphere) of Th(IV) beta-diketonates Th(HFAA)4 and Th(DBM)4, where HFAA and DBM are hexafluoroacetylacetone and dibenzoylmethane respectively, causes them to decompose in hexadecane solutions, forming solid thorium compounds. The first-order rate constants for Th(IV) beta-diketonate degradation were found to be (9.3 +/- 0.8) x 10(-3) for Th(HFAA)4 and (3.8 +/- 0.4) x 10(-3) min-1 for Th(DBM)4, (T = 92 degrees C, I = 3 W cm-2). The rate of the sonochemical reaction increased with the rising beta-diketonate volatility and decreased with the rising hydrocarbon solvent vapor pressure. Solid sonication products consisted of a mixture of thorium carbide ThC2 and Th(IV) beta-diketonate partial degradation products. The average ThC2 particle size was estimated to be about 2 nm. ThC2 formation was attributed to the high-temperature reaction occurring within the cavitating bubble. The thorium beta-diketonate partial degradation products formed in the liquid reaction zones surrounding the cavitating bubbles.

The kinetics of nitrous acid formation were investigated in two-phase tri-n-butylphosphate (TBP)-diluent/HNO3 (1.5-6.0 mol l-1) systems, where diluent is n-C16H34, n-C12H26, n-C9H20 and i-C8H18, under the effect of power ultrasound at 20 kHz frequency under Ar atmosphere. The rate of HNO2 sonochemical formation decreases with the rise in diluent vapor pressure. The HNO2 formed is distributed between the aqueous and organic phases due to its extraction with TBP. The kinetics of HNO2 sonochemical formation in the two-phase system exhibits induction periods due to NOx (NO + NO2) gas reactions in the HNO3 medium. This induction period decreases with increasing HNO3 concentration and ultrasound intensity. The HNO2 steady-state concentration was obtained under long-time sonication as the result of HNO2 sonochemical decomposition. HNO2 decomposes faster under sonication in the aqueous phase than in the organic phase.

The kinetics of hydrogen peroxide formation have been studied during H2O and D2O sonication in the presence of argon and oxygen (f = 22 kHz, I = 3.0 W cm-2, Pac = 0.52 W ml-1, V = 20 ml, T = 20 degrees C). It was found that the sonochemical reaction rate W has a zero order with respect to hydrogen peroxide (H2O, D2O or DHO2) concentration. In argon atmosphere the kinetic isotope effect was found to be equal to alpha = WH2O/WD2O = 2.2 +/- 0.3. The alpha value decreases in H2O-D2O mixtures with increasing H2O concentration. In oxygen atmosphere the isotope effect is not observed (alpha = 1.05 +/- 0.10). It is assumed that the revealed isotope effect is related to the mechanism of water sonolysis including the H2O-Ar* and D2O-Ar* energy transition, where Ar* is an argon atom in an excited state, in nonequilibrium plasma generated by the shock-wave.

The kinetics of Np(V) oxidation was studied in nitric acid solutions in the presence of argon under the effect of power ultrasound (U.S.) with a frequency of 20 kHz and intensity of 1 W.cm(-2). Np(V) sonochemical oxidation in 3-4 mol/L HNO3 solutions was only observed for short-time sonication. Long-time sonication reduces the Np(VI) formed back to Np(V). The use of "anti-nitrous" reagent, such as urea, which exerts a buffering effect related to nitrous acid concentration, helps to stabilise Np(VI) formed under sonication. Ultrasonic treatment of HNO3 solutions does not lead to complete Np(V) oxidation. It is shown that the Np(VI)/Np(V) equilibrium ratio observed for the sonochemical process can be expressed by the same model as the one used for Np(V) oxidation in the absence of ultrasound. It was concluded that the mechanism of Np(V) sonochemical oxidation is related to HNO2 sonochemical formation due to HNO3 sonolysis, followed by Np(V) oxidation with HNO3, catalysed by HNO2.The effect of power U.S. on Np(V) oxidation was also studied in the two-phase solvent extraction system made of tri-n-butylphosphate (30 vol.%)/n-dodecane/HNO3/H2O for the following conditions: U.S. frequency: 20 kHz, I = 1.8 to 3.7 W.cm(-2), T = (32+/-2)degrees C, Ar atmosphere, [NHO3](aq) = 2.8 to 5.2 mol/L. It was shown that sonication of the two-phase mixture causes intense emulsification and Np(V) oxidation to Np(VI), which is mostly extracted into the organic phase. Np was found extracted up to 92% in a single step. For long-time sonication, neptunium concentration in the organic phase decreases due to Np(VI) reduction. The presence of TBP organic phase is sufficient here to buffer the aqueous nitrous acid concentration, so that no "anti-nitrous" reagent is required. As for single phase experiments, Np(V) sonochemical mechanism of oxidation leading to Np(VI) extraction into the organic phase is related to Np(V) oxidation in water by nitric acid, the reaction being catalysed by the nitrous acid formed during nitric acid sonolysis. Nitrogen dioxide, formed as a result of nitrous acid sonochemical decomposition, can also contribute to Np(V) oxidation. For long-time sonication, Np(VI) is reduced to Np(V) in the aqueous phase by the excess nitrous acid formed and, consequently, the neptunium is stripped from the organic phase.

Sonochemical nitrous acid formation was investigated in 0.1–4.0 mol dm−3 aqueous nitric acid solutions under the effect of power ultrasound with 20 kHz frequency. HNO2 steady-state concentration was obtained under long-time sonication; the excess HNO2 formed is decomposed and evoluted from the solution as NO and NO2 gases. The HNO2 steady-state concentration and the HNO2 initial formation rate depend linearly on the HNO3 concentration and acoustic intensity (1.8–3.5 W cm−2) and decrease with rising temperature in the range 21–50°C. The HNO2 formation rate depends on the type of saturating gas as follows: Ar>N2>He>air. NO and O2 are the major gaseous products of HNO3 sonication. The NO2 accumulation of in the gas phase is observed only when the decomposition of HNO2 formed becomes noticeable. The gaseous products formation rates depend on the HNO3 concentration, acoustic intensity and the type of saturating gas. The mechanism of HNO2 sonochemical formation is assumed to be the thermal decomposition of HNO3 in the gaseous vicinity of collapsing bubbles or in the overheated liquid reaction zone surrounding the cavitational bubbles.

The dissolution of pure plutonium metal reference material (99.977%) in a HNO3-HCOOH mixture is considerably enhanced by ultrasonic irradiation with intensity 1 W/cm(2) and frequency 20 kHz under an argon atmosphere. The tested medium is potentially suitable for preparing standard plutonium solution. At [HNO3] = 0.5-1.0 M and [HCOOH] = 1.0-2.0 M the rate of sonochemical dissolution is as much as 17 times higher than that for the unsonicated process. The dissolution of plutonium metal without sonication leads to Pu(III) accumulation in solution. Under sonication at [HNO3] greater than or equal to 1 M Pu(III) is oxidized to Pu(IV) due to HNO2 accumulation as a result of HNO3 sonolysis. It is assumed that ultrasound removes the passivating layer from the metal surface and accelerates of the mass-transfer processes near the extended liquid-solid interface. The formation of CO2 under sonication of HNO3-HCOOH mixtures shows that slow sonochemical denitration also occurs in the system investigated.

The kinetic isotope effect has been observed for gamma-radiolytic reduction of Pb(II) in aqueous formate solutions and the values of the isotope separation coefficient (alpha) for Pb-208/207, Pb-208/206 and Pb-208/204 have been determined.