Zenko Yoshida

Determination of the Hydration Number of Cm(III) in Various Aqueous Solutions

The fluorescence lifetimes of Eu(III) and Cm(III) doped into crystalline lanthanum hydrate compounds were measured to obtain the calibration between the decay constant kobi (the reciprocal of the excited-state lifetime) and the number of water molecules «H2o in the first coordination sphere. The nHl0 of Cm(III) in various aqueous solutions were calculated using the calibration relation obtained and the lifetime in the literature. All of the nH2o values so calculated were chemically reasonable.

The electron transfer at a liquid/liquid interface studied by current-scan polarography at the electrolyte dropping electrode

Abstract Some novel systems are introduced as suitable for observing the electron transfer voltammograms and/or polarograms at the aqueous (W)/nitrobenzene (NB) interface. Among them, the polarographic processes with systems composed of hexacyanoferrate(II), hydroquinone or hydroxyl ion in W/7,7,8,8-tetracyanoquinodimethane (TCNQ) in NB, hexacyanoferrate(III) or Ce4+ in W/ferrocene (FC) or tetrathiafulvalene (TTF) in NB and permanganate in W/tetraphenylborate ion in NB were found to be reversible under appropriate conditions. The relation between the limiting currents in polarograms and the concentration of reactants either in W or NB is presented. On the basis of analysis of reversible polarograms at the W/NB interface and a comparison with voltammograms at a platinum electrode in W or in NB, the half-wave potentials are connected to the oxidation-reduction potentials of the reactants in each individual solution, W or NB.

Luminescence study on solvation of americium(III), curium(III) and several lanthanide(III) ions in nonaqueous and binary mixed solvents

The luminescence lifetimes of An(III) and Ln(III) ions [An=Am and Cm; Ln=Nd, Sm, Eu, Tb and Dy] were measured in dimethyl sulfoxide(DMSO), N,N-dimethylformamide(DMF), methanol(MeOH), water and their perdeuterated solvents. Nonradiative decay rates of the ions were in the order of H2O > MeOH > DMF > DMSO, indicating that O-H vibration is more effective quencher than C-H, C=O, and S=O vibrations in the solvent molecules. Maximal lifetime ratios τD/τH were observed for Eu(III) in H2O, for Sm(III) in MeOH and DMF, and for Sm(III) and Dy(III) in DMSO. The solvent composition in the first coordination sphere of Cm(III) and Ln(III) in binary mixed solvents was also studied by measuring the luminescence lifetime. Cm(III) and Ln(III) were preferentially solvated by DMSO in DMSO-H2O, by DMF in DMF-H2O, and by H2O in MeOH-H2O over the whole range of the solvent composition. The order of the preferential solvation, i.e., DMSO > DMF > H2O > MeOH, correlates with the relative basicity of these solvents. The Gibbs free energy of transfer of ions from water to nonaqueous solvents was further estimated from the degree of the preferential solvation.

The role of non-ionic polyoxyethylene ether surfactants on ion transfer across aqueous/organic solution interfaces studied by polarography with the electrolyte dropping electrode

Abstract The transfer of Li+, Na+, K+, NH+4, Mg2+, Sr2+, and Ba2+ from aqueous solution to 1,2-dichloroethane or nitrobenzene facilitated by polyoxyethylene ethers, Triton X, was studied by current-scan polarography using the aqueous electrolyte dropping electrode. The facilitated ion transfer is attributable to the formation of a hydrophobic complex of metal ion with Triton X adsorbed at the aqueous/organic solution interface, followed by the transfer of the complex from the interface into the organic solution. The stability and the composition of the metal-Triton X complexes were investigated by changing the length of the oxyethylene chain of the Triton X, taking into account the iondipolar bond formation between metal ions and the oxyethylene chain. The adsorption-desorption behavior of the Triton X and metal-Triton X complex was elucidated by referring to drop time curves.

Dissolution Behavior of Uranium Oxides with Supercritical CO2 Using HNO3-TBP Complex as a Reactant

Dissolution behavior of U3O8 and UO2 using supercritical CO2 medium containing HNO3-TBP complex as a reactant was studied. The dissolution rate of the oxides increased with increasing the HNO3/TBP ratio of the HNO3-TBP complex and the concentration of the HNO3-TBP complex in the supercritical CO2 phase. A remarkable increase of the dissolution rate was observed in the dissolution of U3O8 when the HNO3/TBP ratio of the reactant was higher than ca. 1, which indicates that the 2:1 complex, (HNO3)2TBP, plays a role in facilitating the dissolution of the oxides. Half-dissolution time (t½ ) as an indication of the dissolution kinetic was determined from the relationship between the amount of uranium dissolved and the dissolution time (dissolution curve). A logarithmic value of a reciprocal of the t½ was proportional to the logarithmic concentration of HNO3, CHNO3, in the supercritical CO2. The slopes of the (l/t½ ) vs. ln CHNO3 plots for U3O8 and UO2 were different from each other, indicating that the reaction mechanisms or the rate-determining steps for the dissolution of U3O8 and UO2 are different. A principle of the dissolution of uranium oxides with the supercritical CO2 medium is applicable to a method for the removal of uranium from solid matrices.

Correlation between Extraction Equilibrium of Uranium(VI) and Density of CO2 Medium in a HNO3/Supercritical CO2−Tributyl Phosphate System

The extraction equilibrium of U(VI) between a nitric acid solution and a supercritical CO(2) phase containing tributyl phosphate (TBP) is formulated taking into account that (i) a distribution ratio of a metal extracted is a function of a distribution constant of each component involved in the extraction reaction, (ii) the distribution constant is defined as a ratio of solubilities of the component in both phases, and (iii) the solubility in the CO(2) phase is correlated with density of CO(2). A simple linear relationship between the distribution ratio, D(U), of U(VI) and density, ρ, of CO(2) is derived; log D(U) = a log ρ + A + B, in which a is a proportional constant implying the solvation characteristic of the solute in supercritical CO(2), A is a pressure-independent constant, and B is a variable determined by the distribution equilibrium of HNO(3). The equation derived was verified experimentally by the measurement of the distribution ratio of U(VI) and HNO(3) under various conditions of pressure and temperature. A novel concept of selective supercritical fluid extraction of metals by means of pressure-tuning or CO(2) density-tuning was proposed.

Synergistic ion-pair extraction of lanthanide(III) with thenoyltrifluoroacetone and crown ether into 1,2-dichloroethane

ABSTRACT Synergistic extraction of trivalent lanthanides(Ln) was investigated using thenoyltrifluoroacetone(HTTA) and crown ether(CE). Characteristic ion-pair extraction of the lighter Ln(III) was observed with 1,2-dichloroethane containing HTTA and 18-crown-6 or dicychlohexano-18-crown-6, in which the cationic complex, Ln(TTA)2CE+, was formed and extracted. Remarkable increases of an extractability and a selectivity were attained in the synergistic ion-pair extraction of the lighter Ln ions, which could be elucidated on the basis of size-fitting effect in the complex formation of the lighter Ln ions with CE.

Voltammetric interpretation of the potential at an ion-selective electrode, based on current-scan polarograms observed at the aqueous/organic solution interface

The potential-generating process at ion-selective electrodes (ISE) of liquid-membrane types has been interpreted by comparing the ISE potential with the current-scan polarogram which indicates the transfer of a particular ion i(z+) at the aqueous/organic solution (w/o) interface. The potential at zero current, DeltaV(l = 0), in the composite polarogram observed with i(z+) in both w and o, corresponds to the ISE potential. A stable potential giving Nernstian response to the concentration of i(z+) in w is obtained at the ISE only when the w/o interface is depolarized byi(z+). The detection limits are controlled by the final rise and final descent of the residual current in the polarogram. The interference of a second ion,j(z+), in the ISE measurement of i(z+), and the role of an ionophore in the membrane of the ISE can be explained by considering the shift of DeltaV(l = 0) in the composite polarogram ofi(z+) in the presence of j(z+) in w or the ionophore in o. Equations which express the ISE potential, the interference at the ISE, and the effect of an ionophore on the ISE potential have been derived, connected with the polarographic equations for ion-transfer at the w/o interface.

Spectroscopic study of the uranyl hydrolysis species (UO2)2 (OH)22

The behavior of (UO2)2(OH)22+ has been investigated in solid-liquid equilibria under 100%, 8%, 1%, 0.3% and 0.03% CO2 partial pressure as well as in undersaturated systems in equilibrium with air at 24±2°C in 0.1M NaClO4 solutions. From spectroscopic investigations by UV-Vis-and time-resolved laser-induced fluorescence (TRLF) spectroscopies, single component absorption and emission spectra are suggested for the (UO2)2 (OH)22+ species. The lifetime τ22 of the fluorescence emitting electronically excited state of (UO2)2(OH)22+ was determined as τ22 = 2.9 ± 0.9 μs. The formation constant of (UO2)2(OH)22+ was found to be log K22=−5.97 ± 0.06. Interpretation of the experimental data was also made assuming the species (UO2)2(OH)22+, but unsatisfactory results have been obtained.

Luminescence study on preferential solvation of Europium(III) in water/non-aqueous solvent mixtures

Abstract The solvent composition in the first coordination sphere of Eu(III) in water/non-aqueous solvent mixtures was investigated by measuring the luminescence lifetime. The inner-sphere hydration numbers of Eu(III) calculated from the lifetimes gave reasonable values in N , N -dimethylacetamide, N , N -dimethylformamide, dimethyl sulfoxide, formamide, hexamethyl phosphoramide, or N -methylformamide with water system. Eu(III) was preferentially solvated by the non-aqueous solvent in those systems, over the whole range of the non-aqueous solvent mole fraction in the bulk mixtures, X s . The degree of the preferential solvation K PS , defined as the solvent/water mole ratio in the first coordination sphere to that in the bulk solution, varied considerably with the X s in all the systems. The order of the K PS for Eu(III) was hexamethyl phosphoramide>dimethyl sulfoxide> N -methylformamide> N , N -dimethylformamide>formamide> N , N -dimethylacetamide>water>pyridine>methanol>ethanol>acetone>tetrahydrofuran>acetonitrile at X s =0.5. The Gibbs free energy of transfer of Eu(III) from water to non-aqueous solvent was also estimated from the K PS .