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Journal Articles

Securing reversibility of U$$^{V}$$O$$_{2}$$$$^{+}$$/U$$^{VI}$$O$$_{2}$$$$^{2+}$$redox equilibrium in [emim]Tf$$_{2}$$N-based liquid electrolytes towards uranium redox-flow battery

Takao, Koichiro*; Ouchi, Kazuki; Komatsu, Atsushi; Kitatsuji, Yoshihiro; Watanabe, Masayuki

European Journal of Inorganic Chemistry, 27(14), p.e202300787_1 - e202300787_7, 2024/05

https://doi.org/10.1002/ejic.202300787
 Times Cited Count：0 Percentile：0.00(Chemistry, Inorganic & Nuclear)

Electrochemical behavior of U$$^{rm V}$$O$$_{2}$$$$^{+}$$/U$$^{rm VI}$$O$$_{2}$$$$^{2+}$$ in 1-ethyl-3-methylimidazolium bis(trifluoromethyl)sulfonylamide ([emim]Tf$$_{2}$$N) ionic liquid was studied to clarify what are required to attain its redox reversibility for utilizing depleted U as an electrode active material in a redox flow battery. As a result, reversibility of the U$$^{rm V}$$O$$_{2}$$$$^{+}$$/U$$^{rm VI}$$O$$_{2}$$$$^{2+}$$ redox reaction was successfully achieved in use of a glassy carbon working electrode under presence of Cl$$^{-}$$ in [emim]Tf$$_{2}$$N. To improve diffusivity of solutes, [emim]Tf$$_{2}$$N diluted with an auxiliary molecular solvent, N,N-dimethylformamide (DMF). We have succeeded in demonstrating a reversible redox reaction of [U$$^{rm VI}$$O$$_{2}$$Cl$$^{4}$$]$$^{2-}$$ + e$$^{-}$$ = [U$$^{rm V}$$O$$_{2}$$Cl$$^{4}$$]$$^{3-}$$ in the 50:50 v/v [emim]Tf$$_{2}$$N-DMF liquid electrolyte containing Cl$$^{-}$$.

Journal Articles

Fully chelating N$$_{3}$$O$$_{2}$$-pentadentate planar ligands designed for the strongest and selective capture of uranium from seawater

Mizumachi, Takumi*; Sato, Minami*; Kaneko, Masashi; Takeyama, Tomoyuki*; Tsushima, Satoru*; Takao, Koichiro*

Inorganic Chemistry, 61(16), p.6175 - 6181, 2022/04

https://doi.org/10.1021/acs.inorgchem.2c00306
 Times Cited Count：5 Percentile：56.21(Chemistry, Inorganic & Nuclear)

Based on unique 5-fold equatorial coordination of UO$$_{2}$$$$^{2+}$$, water-compatible pentadentate planar ligands, H$$_{2}$$saldian and its derivatives, were designed as strong and selective capture of UO$$_{2}$$$$^{2+}$$ in seawater. In the simulated seawater condition (0.5 M NaCl + 2.3 mM HCO$$_{3}$$$$^{-}$$/CO$$_{3}$$$$^{2-}$$, pH 8), saldian$$^{2-}$$ shows the strongest complexation with UO$$_{2}$$$$^{2+}$$ to form UO$$_{2}$$(saldian) (log$$beta$$$$_{11}$$ = 28.05 $$pm$$ 0.07), which is more than 10 order of magnitude greater than amidoxime-based or -inspired ligand systems most commonly employed for U capture from seawater. Good selectivity for UO$$_{2}$$$$^{2+}$$ from other metal ions coexisting in seawater was also demonstrated.

Journal Articles

Electrochemical studies of uranium (IV) in an ionic liquid-DMF mixture to build a redox flow battery using uranium as an electrode active material

Ouchi, Kazuki; Komatsu, Atsushi; Takao, Koichiro*; Kitatsuji, Yoshihiro; Watanabe, Masayuki

Chemistry Letters, 50(6), p.1169 - 1172, 2021/06

https://doi.org/10.1246/cl.210060
 Times Cited Count：2 Percentile：11.15(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$$^{III}$$/U$$^{IV}$$ couple that could be applied to the anode reaction of the RFB.

Journal Articles

Correlation between intermolecular hydrogen bonds and melting points of uranyl nitrate complexes with cyclic urea derivatives

Suzuki, Tomoya; Takao, Koichiro*; Kawasaki, Takeshi*; Harada, Masayuki*; Nogami, Masanobu*; Ikeda, Yasuhisa*

Polyhedron, 96, p.102 - 106, 2015/08

https://doi.org/10.1016/j.poly.2015.04.034
 Times Cited Count：7 Percentile：49.76(Chemistry, Inorganic & Nuclear)

We have determined crystal structures of UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$(${bf 0a}$)$$_{2}$$ (${bf 0a}$: 2-imidazolidone), UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$(${bf 0b}$)$$_{2}$$ (${bf 0b}$: tetrahydro-2-pyrimidone) and UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$(${bf 1a}$)$$_{2}$$ (${bf 1a}$: 1-methyl-2-imidazolidone) by using single crystal X-ray analysis, and examined correlations between melting points (mps) and intermolecular hydrogen bonds (HBs) of UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$(CU)$$_{2}$$ (CU: cyclic urea derivatives) and UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$(NRP)$$_{2}$$ (NRP: pyrrolidone derivative).

Journal Articles

Precise determination of precipitation yield of uranyl nitrate with $$N$$-alkylated 2-pyrrolidone derivatives

Takao, Koichiro*; Kawata, Yoshihisa*; Nogami, Masanobu*; Harada, Masayuki*; Morita, Yasuji; Nishimura, Kenji*; Ikeda, Yasuhisa*

Journal of Nuclear Science and Technology, 52(2), p.294 - 298, 2015/02

https://doi.org/10.1080/00223131.2014.937782
 Times Cited Count：2 Percentile：16.69(Nuclear Science & Technology)

Yields of precipitated UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$(NRP)$$_{2}$$ (NRP = $$N$$-alkylated 2-pyrrolidone) were precisely determined by considering reduction of the solution volume through the precipitation, which can be estimated from difference in acid concentrations of the liquid phases before and after the precipitation. The studied NRPs were $$N$$-$$n$$-butyl (NBP) and $$N$$-$$n$$-propyl (NProP) derivatives. In both systems, the precipitation yields precisely determined were always higher than those simply calculated from the ratio of uranium concentrations before and after the precipitation. However, the differences between them are in the range of 0.6% - 2.6%. If such a difference is practically negligible, the volume reduction through the precipitation does not have to be taken into account for simplicity of the analytical manipulation.

Journal Articles

Uranyl species in 1-Ethyl-3-methylimidazolium nitrate ([EMI][NO$$_{3}$$]) solution of [EMI]$$_{2}$$[UO$$_{2}$$(NO$$_{3}$$)$$_{4}$$]; First spectrophotometric evidence for existence of [UO$$_{2}$$(NO$$_{3}$$)$$_{4}$$]$$^{2-}$$

Sasaki, Kotoe*; Suzuki, Tomoya*; Arai, Tsuyoshi*; Takao, Koichiro*; Suzuki, Shinichi; Yaita, Tsuyoshi; Ikeda, Yasuhisa*

Chemistry Letters, 43(5), p.670 - 672, 2014/05

https://doi.org/10.1246/cl.131183
 Times Cited Count：7 Percentile：25.32(Chemistry, Multidisciplinary)

no abstracts in English

Journal Articles

Molecular and crystal structures of plutonyl(VI) nitrate complexes with N-alkylated 2-pyrrolidone derivatives; Cocrystallization potentiality of U$$^{VI}$$ and Pu$$^{VI}$$

Kim, S.-Y.; Takao, Koichiro*; Haga, Yoshinori; Yamamoto, Etsuji; Kawata, Yoshihisa; Morita, Yasuji; Nishimura, Kenji*; Ikeda, Yasuhisa*

Crystal Growth & Design, 10(5), p.2033 - 2036, 2010/04

https://doi.org/10.1021/cg100015t
 Times Cited Count：15 Percentile：77.26(Chemistry, Multidisciplinary)

Plutonyl(VI) nitrate complexes with N-cyclohexyl-2-pyrrolidone (NCP) and N-neopentyl-2-pyrrolidone (NNpP) were prepared, and their molecular and crystal structures were determined by single crystal X-ray analysis. The obtained compounds have the similar composition, PuO$$_{2}$$(NO$$_{3}$$)$$_{2}$$(NRP)$$_{2}$$ (NRP = NCP, NNpP), which are analogous to the corresponding U(VI) complexes. Both PuO$$_{2}$$(NO$$_{3}$$)$$_{2}$$(NRP)$$_{2}$$ complexes show typical structural properties of actinyl(VI) nitrates, i.e., hexagonal-bipyramidal geometry consisting of two NRP molecules and two NO$$_{3}$$$$^{-}$$ ions located in trans positions in the equatorial plane of PuO$$_{2}$$$$^{2+}$$ moiety. These findings provide one of criteria in selection of suitable NRP as a precipitation agent for the spent nuclear fuel reprocessing based on the precipitation method.

Journal Articles

Neptunium carbonato complexes in aqueous solution; An Electrochemical, spectroscopic, and quantum chemical study

Ikeda, Atsushi; Tsushima, Satoru*; Takao, Koichiro*; Rossberg, A.*; Funke, H.*; Scheinost, A. C.*; Bernhard, G.*; Yaita, Tsuyoshi; Hennig, C.*

Inorganic Chemistry, 48(24), p.11779 - 11787, 2009/12

https://doi.org/10.1021/ic901838r
 Times Cited Count：35 Percentile：80.02(Chemistry, Inorganic & Nuclear)

The electrochemical behavior and complex structure of Np carbonato complexes have been investigated in aqueous Na$$_{2}$$CO$$_{3}$$ and Na$$_{2}$$CO$$_{3}$$/NaOH solutions at different oxidation states by using cyclic voltammetry, X-ray absorption spectroscopy, and density functional theory calculations. The end-member complexes of penta- and hexavalent Np in 1.5 M Na$$_{2}$$CO$$_{3}$$ with pH = 11.7 have been determined as a transdioxo neptunyl tricarbonato complex, [NpO$$_{2}$$(CO$$_{3}$$)$$_{3}$$]$$^{n-}$$ ($$n$$ = 5 for Np$$^{rm V}$$, and 4 for Np$$^{rm VI}$$). In contrast, the electrochemical oxidation of Np$$^{rm V}$$ in a highly basic carbonate solution of 2.0M Na$$_{2}$$CO$$_{3}$$/1.0M NaOH (pH $$>$$ 13) yielded a stable heptavalent Np complex of [Np$$^{rm VII}$$ O$$_{4}$$(OH)$$_{2}$$]$$^{3-}$$, indicating that the oxidation reaction from Np$$^{rm V}$$ to Np$$^{rm VII}$$ in the carbonate solution involves a drastic structural rearrangement from the transdioxo configuration to a square-planar-tetraoxo configuration, as well as exchanging the coordinating anions from carbonate ions (CO$$_{3}$$$$^{2-}$$) to hydroxide ions (OH$$^{-}$$).

Journal Articles

Development of advanced reprocessing system based on precipitation method using pyrrolidone derivatives as precipitants; Precipitation behavior of U(VI), Pu(IV), and Pu(VI) by pyrrolidone derivatives with low hydrophobicity

Morita, Yasuji; Takao, Koichiro*; Kim, S.-Y.; Kawata, Yoshihisa; Harada, Masayuki*; Nogami, Masanobu*; Nishimura, Kenji*; Ikeda, Yasuhisa*

Journal of Nuclear Science and Technology, 46(12), p.1129 - 1136, 2009/12

https://doi.org/10.3327/jnst.46.1129
 Times Cited Count：18 Percentile：73.96(Nuclear Science & Technology)

A reprocessing system for spent FBR fuels consisting of two precipitation processes has been proposed. In this system, first only U(IV) species are precipitated using pyrrolidone derivative with low hydrophobicity and donicity, and secondly residual U(VI) and Pu(IV, VI) are precipitated simultaneously using pyrrolidone derivative with high precipitation ability. In this study, we have examined precipitation behavior of U(VI), Pu(IV), and Pu(VI) species in nitric acid solutions by using $$N$$-$$n$$-propyl-2-pyrrolidone (NProP), $$N$$-butyl-2-pyrrolidone (NBP), $$N$$-$$iso$$-butyl-2-pyrrolidone (NiBP), or $$N$$-cyclohexyl-2-pyrrolidone (NCP) to select the precipitants for the first precipitation process. As a result, NBP were found to be the most promising precipitant for the first precipitation process.

Journal Articles

Solubility of uranyl nitrate precipitates with $$N$$-Alkyl-2-pyrrolidone derivatives (Alkyl = $$n$$-propyl, $$n$$-butyl, $$iso$$-butyl, and cyclohexyl)

Takao, Koichiro*; Noda, Kyoko*; Nogami, Masanobu*; Sugiyama, Yuichi*; Harada, Masayuki*; Morita, Yasuji; Nishimura, Kenji*; Ikeda, Yasuhisa*

Journal of Nuclear Science and Technology, 46(10), p.995 - 999, 2009/10

https://doi.org/10.3327/jnst.46.995
 Times Cited Count：14 Percentile：66.12(Nuclear Science & Technology)

We have been developing an advanced reprocessing system for spent FBR fuels based on precipitation method using pyrrolidone derivatives. In the present study, the solubility of UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$(NRP)$$_{2}$$ (NRP = $$N$$-alkyl-2-pyrrolidone, alkyl = $$n$$-propyl, $$n$$-butyl, $$iso$$-butyl and cyclohexyl) in aqueous solutions with HNO$$_{3}$$ has been examined. As a result, the solubility of each species of UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$(NRP)$$_{2}$$ generally decreases with increasing concentrations of HNO$$_{3}$$ and NRP ($$C$$(HNO$$_{3}$$) and $$C$$(NRP), respectively). The solubility of UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$(NRP)$$_{2}$$ also depends on the type of NRP; a higher hydrophobicity of NRP generally leads to a lower solubility of UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$(NRP)$$_{2}$$. The logarithms of effective solubility products ($$K$$$$_{rm eff}$$) of UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$(NRP)$$_{2}$$ at different $$C$$(HNO$$_{3}$$) values and 293 K were evaluated.

Journal Articles

Molecular and crystal structures of uranyl nitrate complexes with $$N$$-alkylated 2-pyrrolidone derivatives; Design and optimization of promising precipitant for uranyl ion

Takao, Koichiro*; Noda, Kyoko*; Morita, Yasuji; Nishimura, Kenji*; Ikeda, Yasuhisa*

Crystal Growth & Design, 8(7), p.2364 - 2376, 2008/07

https://doi.org/10.1021/cg7012254
 Times Cited Count：35 Percentile：89.58(Chemistry, Multidisciplinary)

Molecular and crystal structures of UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$(NRP)$$_{2}$$ (NRP = N-alkylated 2-pyrrolidone derivative) have been investigated by using single crystal X-ray analysis, IR and Raman spectroscopies. All UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$(NRP)$$_{2}$$ complexes have typical structural properties of UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$(L)$$_{2}$$ (L = unidentate ligand), i.e., hexagonal-bipyramidal geometry, two NRP and two NO$$_{3}$$$$^{-}$$ located in trans positions in an equatorial plane of the uranyl ion. Observation of the crystals of the uranyl nitrate complexes with N-n-propyl-2-pyrrolidone and N-iso-propyl-2-pyrrolidone indicate the presence of significant voids in the crystal lattices of these compounds. From this result, an approach for construction of efficient packing of UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$(NRP)$$_{2}$$ was proposed. Consequently, it was found that N-iso-butyl-2-pyrrolidone completely satisfies with the requirement for the efficient packing by filling the voids with the alkyl chain.

Journal Articles

Development of advanced reprocessing system based on use of pyrrolidone derivatives as novel precipitants with high selectivity and control ability, 1; Concept of advanced reprocessing system and precipitation behavior of U(VI)

Ikeda, Yasuhisa*; Takao, Koichiro*; Harada, Masayuki*; Morita, Yasuji; Nogami, Masanobu*; Nishimura, Kenji*

Proceedings of International Conference on Advanced Nuclear Fuel Cycles and Systems (Global 2007) (CD-ROM), p.1503 - 1507, 2007/09

We have developed a reprocessing process for spent FBR fuels based on the precipitation method using pyrrolidone derivatives. In previous investigation, N-cyclohexyl-2-pyrrolidone (NCP) is used as a precipitant and a process consisting of selective U precipitation step and U-Pu co-precipitation step was developed. In the present study, in order to examine the applicability of precipitants with lower hydrophobicity than NCP to the selective U precipitation step, we have carried out precipitation experiments of U(VI) by N-butyl-2-pyrrolidone (NBP) and N-propyl-2-pyrrolidone (NProP) and measured decontamination factors of some fission products.

Oral presentation

Development of advanced adsorbent for uranium recovery from seawater based on uranyl coordination chemistry, 1; Molecular design of planar pentadentate ligand and synthesis of its uranyl complex

Takao, Koichiro*; Kaneko, Masashi; Tsushima, Satoru*

no journal, , 

Based on a unique structural character of uranyl ion which favors planar penta-dentate coordination style, we aim to develop advanced absorbent for uranium recovery from seawater. In this study, we designed penta-dentate ligands as the absorber moiety and performed the synthesis and characterization of the uranyl complexes with their ligands.

Oral presentation

Electrode reaction of Ferrocene in ionic liquid-organic solvent mixtures for application to redox flow batteries

Yokota, Yu*; Ouchi, Kazuki; Ueno, Katsuhiro; Takao, Koichiro*; Watanabe, Masayuki

no journal, , 

The electrode reaction of ferrocene/ferrocenium ion in ionic liquid-organic solvent mixtures was investigated for the application of non-aqueous solvents to redox flow batteries. The reversibility of the electrode reaction and the diffusion coefficient of ferrocene were measured to evaluate the mixing ratio of ionic liquids and organic solvents. As a result, the ionic liquid concentration suitable for the redox flow battery was found to be about 0.5 M (Volume ratio: 13%).

Oral presentation

Development of advanced reprocessing system based on precipitation method using high performance pyrrolidone derivatives, 3; Performance evaluation of pyrrolidone derivatives as UO$$_{2}$$$$^{2+}$$ -precipitant from a viewpoint of crystallography

Takao, Koichiro*; Noda, Kyoko*; Nogami, Masanobu*; Sugiyama, Yuichi*; Harada, Masayuki*; Ikeda, Yasuhisa*; Morita, Yasuji; Nishimura, Kenji*

no journal, , 

We have been developing an advanced reprocessing system for spent FBR fuels based on precipitation method using pyrrolidone derivatives. Structural analyses of UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$L$$_{2}$$ (L=11 kinds of pyrrolidone derivatives) have been carried out using X-ray diffraction method to obtain some useful data for the selection of the optimum precipitant. It was found that the U(VI) complex with N-iso-butyl-2-pyrrolidone makes the most compact crystal.

Oral presentation

Development of advanced reprocessing system using high selective and controllable precipitants, 1; Overview of system and recent advances on precipitation behavior of uranyl ions

Nogami, Masanobu*; Kawasaki, Takeshi*; Takao, Koichiro*; Noda, Kyoko*; Sugiyama, Yuichi*; Harada, Masayuki*; Ikeda, Yasuhisa*; Morita, Yasuji; Chikazawa, Takahiro*; Kikuchi, Toshiaki*; et al.

no journal, , 

A reprocessing system for spent FBR fuels based on the two precipitation processes has been proposed. In this system, first only U(VI) species are precipitated using pyrrolidone derivatives (NRP) with low hydrophobicity and donicity, and secondly residual U(VI) and Pu(IV, VI) are precipitated simultaneously using pyrrolidone derivative with high precipitation ability. In order to develop such a reprocessing method, behavior of uranyl ions in HNO$$_{3}$$ has been studied using various novel NRP. In this presentation, recent advances on precipitation behavior and of uranyl ions and calcination of U(VI)-NRP will be introduced.

Oral presentation

XAFS study on effect of molybdenum addition on photo-induced particle formation of palladium

Saeki, Morihisa; Matsumura, Daiju; Yomogida, Takumi; Taguchi, Tomitsugu; Tsuji, Takuya; Kusano, Shogo*; Miyazaki, Tatsuya*; Takao, Koichiro*; Oba, Hironori; Nakashima, Nobuaki*

no journal, , 

no abstracts in English

Oral presentation

Development of advanced reprocessing system using high selective and controllable precipitants, 9; Investigation of stability of novel pyrrolidone precipitants against radiation and heat

Nogami, Masanobu*; Noda, Kyoko*; Takao, Koichiro*; Sugiyama, Yuichi*; Harada, Masayuki*; Ikeda, Yasuhisa*; Kawata, Yoshihisa; Morita, Yasuji; Nishimura, Kenji*

no journal, , 

We have been developing an advanced reprocessing system for spent FBR fuels based on precipitation method using pyrrolidone derivatives. The present study deals with durability of new precipitants with low and high hydrophobicity against $$gamma$$-irradiation and heating. Results showed that the precipitants with low hydrophobicity, N-n-butyl-2-pyrrolidone, N-propyl-2-pyrrolidone and N-iso-butyl-2-pyrrolidone, have enough durability against $$gamma$$-irradiation. The precipitants with high hydrophobicity, N-cyclohexyl-2-pyrrolidone, N-(1,2-dimethyl)propyl-2-pyrrolidone and N-neopenthyl-2-pyrrolidone, also have enough durability but gave lower precipitation yield when they irradiated with higher dose rate. The precipitation ability of all the precipitants did not changed by the heating at 50$$^{circ}$$C for three days.

Oral presentation

Electrochemical reaction of Uranium(IV) chloride in an ionic liquid-DMF mixture

Ouchi, Kazuki; Komatsu, Atsushi; Takao, Koichiro*; Kitatsuji, Yoshihiro; Watanabe, Masayuki

no journal, , 

The electrode reaction of uranium (IV) tetrachloride in an ionic liquid-DMF mixture was studied in order to build a redox flow battery (RFB) using U as an electrode active material. We found the quasi-reversible U(III)/U(IV) reaction that the formal potential is almost constant at -1.559 $$pm$$ 0.003 V. This reaction could be applied to the negative electrode reaction of the RFB.

Oral presentation

Relationship between melting points and crystal structures of uranyl nitrate complexes bearing cyclic urea precipitants

Suzuki, Tomoya; Takao, Koichiro*; Kawasaki, Takeshi*; Sasaki, Yuji; Harada, Masayuki*; Nogami, Masanobu*; Ikeda, Yasuhisa*

no journal, , 

An advanced reprocessing system for spent FBR fuels has been proposed on the basis of selective precipitation ability of pyrrolidone or cyclic urea derivatives. In this process, U and Pu are recovered through two precipitation process after dissolution of spent FBR fuels in HNO$$_{3}$$ solution. In our previous study, it was found that hydrophilic compounds which can form uranyl nitrate complexes with high melting points have high selective precipitation ability to U(VI). In this study, molecular and crystal structures of uranyl nitrate complexes bearing cyclic urea ligands were examined to clarify requirements for forming the U(VI) complexes with high melting points.

26 (Records 1-20 displayed on this page)