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Ouchi, Kazuki; Tsukahara, Takehiko*; Brandt, A.*; Muto, Yuki*; Nabatame, Nozomi*; Kitatsuji, Yoshihiro
Analytical Sciences, 37(12), p.1789 - 1794, 2021/12
We attempted to scale down a separation process of uranium (U) using the microchip column loaded with anion exchange resin to develop safety and waste-reducing separation technique. The ideal separation performance of U was obtained by the properly design of a microchannel. The concentration of U in seawater as a real-world sample could be quantified with the prepared microchip column. It indicates that the microchip column is sufficiently practical. Compared to separation of U with a general column, the column size was successfully scaled down to 
1/5000.
Ouchi, Kazuki; Komatsu, Atsushi; Takao, Koichiro*; Kitatsuji, Yoshihiro; Watanabe, Masayuki
Chemistry Letters, 50(6), p.1169 - 1172, 2021/06
Times Cited Count：0 Percentile：0(Chemistry, Multidisciplinary)The electrochemical behavior of uranium (IV) tetrachloride in ionic liquid-DMF mixture was studied for first time in order to build a redox flow battery (RFB) using U as an electrode active material. We found a quasi-reversible U
/U
couple that could be applied to the anode reaction of the RFB.
Haraga, Tomoko; Ouchi, Kazuki; Sato, Yoshiyuki; Hoshino, Hitoshi*; Tanana, Rei*; Fujihara, Takashi*; Kurokawa, Hideki*; Shibukawa, Masami*; Ishimori, Kenichiro; Kameo, Yutaka; et al.
Analytica Chimica Acta, 1032, p.188 - 196, 2018/11
Times Cited Count：6 Percentile：33.4(Chemistry, Analytical)The development of safe, rapid and highly sensitive analytical methods for radioactive samples, especially actinide (An) ions, represents an important challenge. Here we propose a methodology for selecting appropriate emissive probes for An ions with very low consumption and emission of radioactivity by capillary electrophoresis-laser-induced fluorescence detection (CE-LIF), using a small chemical library of probes with eight different chelating moieties. It was found that the emissive probe, which possesses the tetradentate chelating moiety, was suitable for detecting uranyl ions. The detection limit for the uranyl-probe complex using CE-LIF combined with dynamic ternary complexation and on-capillary concentration techniques was determined to be 0.7 ppt. This method was successfully applied to real radioactive liquid samples collected from nuclear facilities.
Ouchi, Kazuki; Otobe, Haruyoshi; Kitatsuji, Yoshihiro; Yamamoto, Masahiro
ECS Transactions, 75(27), p.51 - 57, 2017/01
Times Cited Count：0 Percentile：0.59We investigated the deposition of U(IV) following a valence change of U as electrodeposition using an electrochemical quartz crystal microbalance (EQCM). When measurements of the reduction of U(VI) in a weak acid solution were performed, deposits of U(IV) were observed on the electrode surface. From deposition rates, pH dependence of them, and oxidation potentials of deposits, we proposed the following deposition mechanism. The deposition is divided into the three phases; First, in the induction phase, U(IV) produced by the disproportionation forms U(IV) hydroxide nucleus. Next, in the growth phase, U(IV) deposits begin to grow. In this phase, the deposits catalyze the reduction of U(V) to U(IV), resulting an increase of the reduction current. Finally, in the transformation phase, U(IV) hydroxide species transform into U dioxide having more stable state.
Sato, Takahiro*; Iwasaki, Atsushi*; Ishibashi, Kazuki*; Okino, Tomoya*; Yamanouchi, Kaoru*; Adachi, Junichi*; Yagishita, Akira*; Yazawa, Hiroki*; Kannari, Fumihiko*; Aoyama, Makoto; et al.
Europhysics News, 42(5), P. 10, 2011/09
The resonant and non-resonant two-photon single ionization processes of He were investigated using intense free electron laser light in the extreme ultraviolet (XUV) region (53.4-61.4 nm) covering the 1s-2p and 1s-3p resonant transitions of He. On the basis of the dependences of the yield of He
on the XUV light-field intensity at 53.4, 58.4, 56.0 and 61.4 nm, the absolute values of the two-photon ionization cross sections of He at the four different wavelengths and their dependence on the light-field intensity were determined for the first time.
Sato, Takahiro*; Iwasaki, Atsushi*; Ishibashi, Kazuki*; Okino, Tomoya*; Yamanouchi, Kaoru*; Adachi, Junichi*; Yagishita, Akira*; Yazawa, Hiroki*; Kannari, Fumihiko*; Aoyama, Makoto; et al.
Journal of Physics B; Atomic, Molecular and Optical Physics, 44(16), p.161001_1 - 161001_5, 2011/08
Times Cited Count：33 Percentile：84.31(Optics)The resonant and non-resonant two-photon single ionization processes of He were investigated using intense free electron laser light in the extreme ultraviolet (XUV) region (53.4-61.4 nm) covering the 1s-2p and 1s-3p resonant transitions of He. On the basis of the dependences of the yield of He on the XUV light-field intensity at 53.4, 58.4, 56.0 and 61.4 nm, the absolute values of the two-photon ionization cross sections of He at the four different wavelengths and their dependence on the light-field intensity were determined for the first time.
Iijima, Kazuki; Kurosawa, Seiichi*; Tobita, Minoru*; Kibe, Satoshi*; Ouchi, Yuji*
no journal, ,
Diffusion behavior of humic acid in compacted bentonite was investigated by through-diffusion method. Concentration profile and molecular weight distribution of humic acid in the compacted bentonite indicate that only low molecular weight fraction of humic acid is likely to diffuses. Difference of diffusion behavior arising from difference of molecular weight is considered to be taken into account in evaluation of diffusion parameters.
Iijima, Kazuki; Kurosawa, Seiichi*; Kibe, Satoshi*; Tobita, Minoru*; Ouchi, Yuji*
no journal, ,
Diffusion behavior of humic acid and Nd in the presence of humic acid was investigated and modeled. Breakthrough of humic acid is observed in 0.1 and 1M NaCl with 1.2-1.6 Mg/m
dry density of compacted bentonite. The presence of humic acid facilitates the migration of Nd. Diffusion Parameters were evaluated from experimental results using the one dimensional diffusion model in which migration of several Nd species with different diffusion behaviors keeping equilibrium in parallel was taken into account. Obtained diffusion parameters for humic acid and Nd will be used for prediction of diffusion behavior of radionuclides in the presence of humic acid under various conditions.
Sato, Yoshiyuki; Haraga, Tomoko; Nakano, Yuta*; Ouchi, Kazuki; Ito, Yuki*; Ishimori, Kenichiro; Takahashi, Kuniaki; Saito, Shingo*
no journal, ,
For the development of a simple and rapid analytical method for actinides (Thorium, Uranium, Neptunium, Plutonium, Americium and Curium) in radioactive wastes, capillary electrophoresis-laser -induced fluorescence detecting method (CE-LIF) was studied. In this research, newly synthesized eight probes whose chelating group were acyclic or macrocyclic were applied to the detection of actinides using CE-LIF. As a result, Thorium and Uranium were successfully detected and separated from other actinide ions applied to octadenate acyclic probe and tetradenate planer probe, respectively. Neptunium was detected using hexadenate or heptadenate probes whose chelating groups were acyclic or macrocyclic. Plutonium was detected applied to hexadenate or octadenate acyclic probes. Americium and Curium were detected applied to seven probes except for tetradenate planer probe.
Haraga, Tomoko; Sato, Yoshiyuki; Ouchi, Kazuki*; Shibukawa, Masami*; Ishimori, Kenichiro; Kameo, Yutaka; Saito, Shingo*
no journal, ,
Uranium is an important nuclide for the analysis of radioactive wastes from nuclear fuel cycle facilities. In order to achieve simple and rapid analysis of uranium, capillary electrophoresis-laser-induced fluorescent detection method (CE-LIF) is one of the potential candidates. In this study, a highly emissive probe of uranyl ion suitable for CE-LIF was developed. The detection and separation of uranyl ion were examined using several new emissive complexing probes, each of which possessed a fluorophore and a different chelating moiety. Using a tetradentate probe, phenanthroline dicarboxylic acid chelating moiety, the highly sensitive fluorescent detection of uranium was successfully achieved. The detection limit of mid-ppt levels was determined, and coexisting matrix metal ions, such as Ca
, Co, Cs, Sr, lanthanide ions and others, do not disturb the detection of uranium. This method has a great potential to be applied to analysis of radioactive waste samples.
Haraga, Tomoko; Nakano, Yuta*; Sato, Yoshiyuki; Ouchi, Kazuki*; Hirose, Kazuki*; Shibukawa, Masami*; Ishimori, Kenichiro; Kameo, Yutaka; Saito, Shingo*
no journal, ,
no abstracts in English
Kitatsuji, Yoshihiro; Ouchi, Kazuki; Otobe, Haruyoshi
no journal, ,
Electrolytic reactions of Neptunium ions in a weakly acid solution were investigated by using gold electrode. It was reported previously that electrolytic reduction of Neptunium (V) ion based on mediator reaction with Np(III)/Np(IV) couple was observed in the acidic solution when bulk electrolysis was carried out at the potential around -0.2 V versus Ag/AgCl reference electrode. The reduction of Np(V), however, was not observed at the pH higher than 2. This is attributable to low reaction rate of electron exchange reaction between Np(V) and Np(III). Electrode reaction of Np(V) at more negative potential was investigated by cyclic voltammetry. The current peak due to reduction of Np(V) was observed at ca. -0.75 V, and oxidation current was appeared at +0.5 V. The reactions was determined to be reduction of Np(V) and oxidation of deposited species of reduction product of Np on the electrode. It was found that stripping current due to oxidation of deposit was saturated in spite of longer preelectrolysis time. This phenomenon is different from uranium.
Ouchi, Kazuki; Otobe, Haruyoshi; Kitatsuji, Yoshihiro
no journal, ,
In this study, we investigated the relationship between reduction process and formation of aggregates by measuring electrochemical quartz crystal microbalance (EQCM). When EQCM measurements of the reduction of U(V) to U(IV) in weakly acid solution were performed, the frequency was changed negatively. This indicates that aggregates of U(IV) were formed on the electrode. We consider that aggregates form in the three steps from the deposition rate; the induction step (
start deposition), early stage aggregation step (deposition amount 4 nmol) and secondary stage aggregation step (deposition amount 
4 nmol). The pH dependence of the reduction and deposition rate was investigated. The U(IV) aggregates formed at more than pH3.1. When pH was higher, the induction time was fast, and aggregation rates at early and secondary stage were high. This suggests that a U hydroxide relates to the formation of aggregates.
Kitatsuji, Yoshihiro; Ouchi, Kazuki; Otobe, Haruyoshi; Kihara, Sorin*
no journal, ,
Electrolytic reduction of neptunium ion in the weak acidic solution was investigated. On the cyclic voltammogram of Np(V) in the solution of pH 3.8, reduction and deposition of Np was observed. Stripping current due to oxidation of deposited Np was also appeared. Stripping voltammetry after preelectrolysis at definite potential was carried out. Stripping currents were almost constant despite variation of preelectrolysis time and concentration of Np(V). Difference of reduction-deposition behavior between U and Np was discussed.
Ouchi, Kazuki; Kitatsuji, Yoshihiro; Otobe, Haruyoshi; Kihara, Sorin*
no journal, ,
In this study, we investigated the relationship between reduction process and aggregation of uranium by measuring electrochemical quartz crystal microbalance (EQCM). When EQCM measurements of the reduction of U(V) to U(IV) in weakly acid solution were performed, the frequency was changed negatively. This indicates that aggregates of U(IV) were formed on the electrode. We consider that aggregates form in the three steps from the deposition rate; the induction step ( start deposition), metastable stage aggregation step and stable stage aggregation step. The pH dependence of the reduction and deposition rate was investigated. The U(IV) aggregates formed at more than pH 3.1. When pH was higher, the induction time was fast, and aggregation rates at early and secondary stage were high. This suggests that a U hydroxide relates to the formation of aggregates.
Ouchi, Kazuki; Otobe, Haruyoshi; Kitatsuji, Yoshihiro
no journal, ,
In previous study, it was found that microparticles of U(IV) formed in reduction process of U(V) enhanced the rate of the disproportionation and the electrolytic reduction of U(V). In this study, we investigated the relationship between reduction process and formation of microparticles by measuring electrochemical quartz crystal microbalance (EQCM). When EQCM measurements of the reduction of U(VI) in a weakly acid solution were performed, the frequency was changed negatively. This indicates that aggregates of U(IV) were formed on the electrode surface. We consider that aggregates form in the three steps from deposition rates; the induction step (start deposition), metastable aggregation step (temporary fast rate) and stable aggregation step (constant rate). The pH dependence of the deposition rate was investigated. When pH was higher, the deposition rates at metastability and stability step were high. This suggests that a U hydroxide relates to the formation of aggregates.
Kitatsuji, Yoshihiro; Ouchi, Kazuki; Otobe, Haruyoshi
no journal, ,
Electrolytic reduction of actinide ions in the weak acidic solution was investigated by focusing the relation between redox and aggregation of the ions. Constant potential electrolysis of uranium (VI) ion was carried out using Au electrode. It was found that U(VI) was rapidly reduced to U(V) and further reduction to U(IV) was not observed at the beginning of electrolysis when acidity of the solution was lower than pH 2. However, the reduction of U(V) to U(IV) is catalyzed by the reduction product which is U(IV) deposited on the electrode. Unlike uranium, the electrodeposition occurred quickly with electrode reduction of Np(V). Then the reduction of Np(V) was inhibited by formation of deposit layer on the electrode.
Kitatsuji, Yoshihiro; Ouchi, Kazuki; Otobe, Haruyoshi
no journal, ,
Redox behaviors of actinide ions in a low-acid solution are complicated and have been unclear, because they tend to form hydroxide complexes, colloids and precipitates. Recently, autocatalysis of the reduction of U(V) to U(IV) in the solution where U(IV) forms hydroxide colloid was reported; U(IV) colloid formed as reduction product catalyzes the electrolytic reduction of U(V). In this study, possibility of catalysis of Zr(IV) colloid which was analogous of U(IV) colloid on the reduction of U(V) was investigated. When U(VI) was electrolyzed at a constant potential in order to reduce to U(V) in the solution of pH 3.0 containing 10 mM Zr(IV), the increase of the reduction current was observed in initial stage of electrolysis. This results indicates that U(VI) was reduced further to U(IV) without catalysis of U(IV) colloid, and that Zr(IV) colloid also acts as catalyst. Intensity of catalysis depends on concentration of Zr(IV), condition of preparing colloid and acidity of the solution.
Hattori, Takanori; Sano, Asami; Arima, Hiroshi*; Komatsu, Kazuki*; Funakoshi, Kenichi*; Abe, Jun*; Machida, Shinichi*; Ouchi, Keiichi*; Okazaki, Nobuo*
no journal, ,
PLANET is a high-pressure neutron beamline recently constructed at MLF in J-PARC. Most characteristic feature of the beamline is to possess the large six-axis multi-anvil high-pressure ATSUHIME press, which enables in-situ neutron diffraction under high pressure and high temperature condition up to 10 GPa and 2000 K. Smaller presses, a Paris-Edinburgh press and Mito cell, are also available and the accessible PT conditions with each device are 20 GPa at room temperature and 5 GPa at 77 K, respectively. The beamline is equipped with incident slits and receiving collimators that eliminates parasitic scattering from the high-pressure cell assembly to obtain clean data. The high performance of the diffractometer and low-parasitic scattering characteristics enables precise structure determination of crystals and liquids under high pressure and temperature conditions. In this presentation, the specification of the PLANET and recent results obtained at PLANET are introduced.
Ouchi, Kazuki; Kitatsuji, Yoshihiro; Otobe, Haruyoshi; Kihara, Sorin*
no journal, ,
In this study, we investigated the change of the deposition amount on standing to obtain knowledge of the chemical state change of electrodeposited U(IV). After electrolysis was stopped, the U deposits on the electrode surface decreased regardless of the presence or absence of U(VI) ion. When the oxidation potential (+0.2 V) was applied, the decrease of the deposits was faster than that of stopping electrolysis. On the other hand, when the reduction potential (-0.35 V) was applied, the decrease of the deposits was not observed. The decrease rate of deposits applied oxidation potential was very fast soon after the start of electrolysis and turned to be slow subsequently. This suggests that U deposition species transform into U oxide having more stable state electrochemically.
