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Oxidation of Np(IV) with nitric acid in the presence of Ru/SiO catalysts was studied by spectrophotometry. The catalytic oxidation of Np(IV) in nitric acid solutions occurs even in the presence of hydrazine. The mechanism of Ru-catalyzed oxidation of Np(IV) with nitric acid was suggested on the basis of the kinetic data. The effect of the Ru nanoparticle size on the activation energy of the catalytic oxidation of Np(IV) was revealed. It shows that the heterogeneous-catalytic reaction is structure-sensitive (positive size effect). [ABSTRACT FROM AUTHOR]

The reduction of Np(V) with hydrazine in HNO solution in the presence of Ru/SiO catalysts was studied by spectrophotometry. The back oxidation of Np(IV) with nitric acid, also catalyzed by ruthenium, occurs concurrently with the Np(V) reduction with hydrazine. The contribution of each process is determined by the HNO concentration. The mechanism of the ruthenium-catalyzed reduction of Np(V) with hydrazine was suggested on the basis of the kinetic data. The effect of the size of Ru nanoparticles on the activation energy of the catalytic reduction of Np(V), characterizing the structural sensitivity of the heterogeneous-catalytic reaction (positive size effect), was revealed. [ABSTRACT FROM AUTHOR]

The behavior of Pu(IV–VI) in CH3COOH-CH3COOLi solutions was studied by spectrophotometry. The Pu(VI) absorption spectrum changes essentially with an increase in the CH3COOLi concentration. Owing to formation of Pu(VI) acetate complexes, the maximum of the main absorption band is shifted from 830.6 (in HClO4 solution) to 845 nm, with the band intensity decreasing by a factor of approximately 8. The Pu(V) and Pu(IV) absorption spectra at low concentrations of acetate ions vary insignificantly relative to the spectra in noncomplexing media. With an increase in the acetate concentration in the system to 1–3 mM, the effect of Pu(V) complexation on its absorption spectrum becomes noticeable (the absorption intensity considerably decreases), whereas the Pu(IV) absorption spectra remain essentially unchanged. Solutions containing 1–2 mM Pu(V) and 0.2–0.5 M CH3COOLi remain unchanged at 18–25°C for 2 days. In solutions with [CH3COOLi] = 1–3 M, Pu(V) disproportionates with the formation of soluble Pu(VI) complexes and a suspension of Pu(IV) hydroxide. Introduction of CH3COOH to a concentration of 0.1–1.0 M prevents the formation of a suspension of Pu(IV) hydroxide, but only up to a temperature of 45°C. The Pu(V) loss follows a second-order rate law, with the reaction products, Pu(IV) and Pu(VI), accelerating the Pu(V) consumption. The reaction rate at a constant concentration of acetate ions is proportional to [H+]. The reaction order with respect to Ac− ions is close to 1.6. The activation energy of the Pu(V) disproportionation in the range 19–45°C is estimated at 74.5 kJ mol−1. It is assumed that the disproportionation mechanism involves the formation of dimers from Pu(V) acetate complexes and aqua ions, their protonation, and decomposition with the transformation into Pu(IV) and Pu(VI). [ABSTRACT FROM AUTHOR]

Deep eutectic solvents (DESs) were investigated as extracting solvent for headspace single-drop microextraction (HS-SDME). The extraction efficiency of 10 DESs mainly composed of tetrabutylammonium bromide (N 4444 Br) and long-chain alcohols was evaluated for the extraction of terpenes from six spices (cinnamon, cumin, fennel, clove, thyme, and nutmeg). The DES composed of N 4444 Br and dodecanol at a molar ratio of 1:2 showed the highest extraction efficiency and was selected to conduct the extractions of terpenes in the rest of the study. HS-SDME was optimized by design of experiments. Only two parameters from the four studied showed a significant influence on the efficiency of the method: the extraction time and the extraction temperature. The optimal extraction conditions were determined by response surface methodology. All extracts were analyzed by gas chromatography coupled to mass spectrometry (GC-MS). More than 40 terpenes were extracted and identified in nutmeg, the richest extract in terpenes in this study. Quantitative analysis based on 29 standards was conducted for each extract. Good linearity was obtained for all standards (R 2  > 0.99) in the interval of 1 to 500 μg/g. Limits of quantification ranged from 0.47 μg/g (borneol) to 86.40 μg/g (α-farnesene) with more than half of the values under 2 μg/g. HS-SDME is simple, rapid, and cheap compared with conventional extraction methods. The use of DESs makes this extraction method "greener" and it was shown that DESs can be suitable solvents for the extraction of bioactive compounds from plants.

The solubilities of C1C4im(+) and Tf2N(-) in nitric aqueous phases have been measured for several ligand types and concentrations (0.04 M tributylphosphine oxide, 0.05 M N,N'-dimethyl-N,N'-dibutylmalonamide, 0.10 M 1-methyl-3-[4-(dibutylphosphinoyl)butyl]-3H-imidazol-1-ium bis(trifluoromethylsulphonyl)imidate, and 1.1 M N,N-dihexyloctanamide). The data evidence a significant difference between the solubilities of the cations and anions of the ionic liquid as a consequence of several ion-exchange and/or ion-pairing mechanisms involving all ions present in the system as well as the protonation/nitric-extraction ability of the ligand.

The complex formation of nitrate ions with nickel(II) in dry [C4mim][Tf2N] ionic liquid (IL) was investigated by means of UV-visible spectrophotometry, isothermal titration calorimetry (ITC), extended X-ray absorption fine structure spectroscopy (EXAFS), and molecular dynamics (MD) simulations. EXAFS spectroscopy and MD simulations show that the solvated Ni(II) cation is initially coordinated by the oxygens of the [Tf2N](-) anion of IL, which can behave either as mono- or bidentate. Spectroscopic and thermodynamic data show that Ni(II) is able to form up to three stable mononuclear complexes with nitrate in this solvent. The stability constants for Ni(NO3)j complexes (j = 1-3) calculated from spectrophotometry and ITC experiments decrease in the order log K1 > log K2 > log K3. The formation of the first two species is enthalpy-driven, while the third species is entropy-stabilized. The UV-vis spectra of solutions containing different nitrate/Ni(II) ratios show that the metal ion retains the six-coordinate geometry. Furthermore, the EXAFS evidences that nitrate is always bidentate. Molecular dynamics simulations show that the [Tf2N](-) anions bind Ni(II) through the sulfonyl oxygen atoms and can coordinate either as monodentate or chelate. The analysis of the MD data shows that introduction of nitrates in the first coordination sphere of the metal ion results in remarkable structural rearrangement of the ionic liquid.

We present new results on the liquid-liquid extraction of uranium (VI) from a nitric acid aqueous phase into a tri-n-butyl phosphate/1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (TBP/[C4 mim][Tf2 N]) phase. The individual solubilities of the ionic-liquid ions in the upper part of the biphasic system are measured over the whole acidic range and as a function of the TBP concentration. New insights into the extraction mechanism are obtained through the in situ characterization of the extracted uranyl complexes by coupling UV/Vis and extended X-ray absorption fine structure (EXAFS) spectroscopy. We propose a chemical model to explain uranium (VI) extraction that describes the data through a fit of the uranyl distribution ratio DU . In this model, at low acid concentrations uranium (VI) is extracted as the cationic complex [UO2 (TBP)2 ](2+) , by an exchange with one proton and one C4 mim(+) . At high acid concentrations, the extraction proceeds through a cationic exchange between [UO2 (NO3 )(HNO3 )(TBP)2 ](+) and one C4 mim(+) . As a consequence of this mechanism, the variation of DU as a function of TBP concentration depends on the C4 mim(+) concentration in the aqueous phase. This explains why noninteger values are often derived by analysis of DU versus [TBP] plots to determine the number of TBP molecules involved in the extraction of uranyl in an ionic-liquid phase., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)