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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：2 Percentile：36.89(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 $_{11}$ = 28.05 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

Dinuclear complexes of tetravalent cerium in an aqueous perchloric acid solution

Ikeda, Atsushi*; Tsushima, Satoru*; Hennig, C.*; Yaita, Tsuyoshi; Bernhard, G.*

Dalton Transactions, 41(24), p.7190 - 7192, 2012/06

https://doi.org/10.1039/c2dt12406h

Times Cited Count：46 Percentile：88.91(Chemistry, Inorganic & Nuclear)

Journal Articles

Redox-dependant sulphate coordination of neptunium in aqueous solutions

Hennig, C.*; Ikeda, Atsushi; Tsushima, Satoru*; Scheinost, A. C.*

ESRF Highlights 2009, p.84 - 85, 2010/02

The sulphate coordination to neptunium ion has been investigated in aqueous solution by X-ray absorption spectroscopy. The results suggest that the coordination mode of sulphate ion strongly depends the oxidation state of neptunium, and changes from uni- to bidentate modes.

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：34 Percentile：79.72(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 $_{3}$ ) $_{3}$ ] $^{n-}$ ( = 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

Speciation and structural study of U(IV) and -(VI) in perchloric and nitric acid solutions

Ikeda, Atsushi; Hennig, C.*; Tsushima, Satoru*; Scheinost, A. C.*; Bernhard, G.*; Yaita, Tsuyoshi

Inorganic Chemistry, 48(15), p.7201 - 7210, 2009/07

https://doi.org/10.1021/ic9004467

Times Cited Count：73 Percentile：94.89(Chemistry, Inorganic & Nuclear)

Speciation and complex structure of U(IV) and U(VI) are studied in aqueous acidic solutions of HClO $_{4}$ and HNO $_{3}$ by means of UV-visible-NIR and X-ray absorption spectroscopies, and density functional theory (DFT) calculations. A spherical coordinating tetravalent cation of U $^{4+}$ is surrounded by 9-10 water molecules in the primary coordination sphere in 1.0 M HClO $_{4}$ , while it forms a not-well-ordered colloidal compound of UO $_{rm 2+x}$ (x = 0.2) mixture in a lower acidic concentration of 0.1 M HClO $_{4}$ . U(VI) exists as a transdioxo uranyl cation, UO $_{2}$ $^{2+}$ , and forms a 5-fold pure hydrate complex of [UO $_{2}$ (H $_{2}$ O) $_{5}$ ] $^{2+}$ in 1.0 M HClO $_{4}$ . The water molecules in the pure hydrate complexes of U(IV) and U(VI) are successively replaced by planar bidentate coordinate nitrate ions (NO $_{3}$ $^{-}$ ) as a function of increasing HNO $_{3}$ concentration. The presence of unidentate coordinate nitrate complexes or tetranitrato U(VI) complexes is less probable in the present HNO $_{3}$ system.

Journal Articles

The Sulfate coordination of Np(IV), Np(V), and Np(VI) in aqueous solution

Hennig, C.*; Ikeda, Atsushi; Tsushima, Satoru*; Scheinost, A. C.*

Inorganic Chemistry, 48(12), p.5350 - 5360, 2009/06

https://doi.org/10.1021/ic9003005

Times Cited Count：42 Percentile：85.14(Chemistry, Inorganic & Nuclear)

Coordination and redox behavior of Np(IV), Np(V) and Np(VI) sulfate in aqueous solution has been investigated by Np L3-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, cyclic voltammetry and density functional theory (DFT) calculations. TNp(VI) is coordinated by sulfate in bidentate (RNp-S = 3.12 A) and monodentate (RNp-S = 3.61 A) modes at a low sulfate concentration of [SO $_{4}$ $^{2-}$ ]/[NpO $_{2}$ $^{2+}$ ] = 1. At higher [SO $_{4}$ $^{2-}$ ]/[NpO $_{2}$ $^{2+}$ ] ratios bidentate coordination prevails. Approximately two bidentate sulfate groups are coordinated to Np(VI) at 2.0 M SO $_{4}$ $^{2-}$ and pH 1.1. Np(V) is coordinated by sulfate in bidentate (RNp-S = 3.16 A) and monodentate (RNp-S = 3.67 A) modes. However, sulfate coordination is less pronounced here and does not exceed in total one SO $_{4}$ $^{2-}$ ligand in a solution of 2.0 M SO $_{4}$ $^{2-}$ . The redox couple Np(VI)/Np(V) is reversible at low [SO $_{4}$ $^{2-}$ ]/[NpO $_{2}$ $^{2+}$ ] ratio and becomes irreversible at high sulfate concentration due to structural rearrangement of the sulfate ligands.

Journal Articles

Structural determination of individual chemical species in a mixed system by iterative transformation factor analysis-based X-ray absorption spectroscopy combined with UV-visible absorption and quantum chemical calculation

Ikeda, Atsushi; Hennig, C.*; Rossberg, A.*; Tsushima, Satoru*; Scheinost, A. C.*; Bernhard, G.*

Analytical Chemistry, 80(4), p.1102 - 1110, 2008/01

https://doi.org/10.1021/ac7021579

Times Cited Count：25 Percentile：60.21(Chemistry, Analytical)

A multitechnique approach using extended X-ray absorption fine structure spectroscopy based on iterative transformation factor analysis, UV-visible absorption spectroscopy, and quantum chemical calculations has been performed for identifying the complex structure of individual U(VI) nitrate species.

Journal Articles

Reduction behavior of uranium in the presence of citric acid

Suzuki, Yoshinori; Nankawa, Takuya; Yoshida, Takahiro*; Ozaki, Takuo; Onuki, Toshihiko; Francis, A. J.; Tsushima, Satoru*; Enokida, Yoichi*; Yamamoto, Ichiro*

Radiochimica Acta, 94(9-11), p.579 - 583, 2006/11

https://doi.org/10.1524/ract.2006.94.9-11.579

Times Cited Count：20 Percentile：78.89(Chemistry, Inorganic & Nuclear)

We examined the reduction behavior of UO $_{2}$ $^{2+}$ in citrate media at pH 2.0-7.0 by column electrodes. At pH 2.0, UO $_{2}$ $^{2+}$ was reduced to U(IV) through a one-step reduction process, while it was reduced to U(IV) through a two-step reduction process at pH 3.0-5.0. The reduction potential of UO $_{2}$ $^{2+}$ shifted to lower values with an increase in pH from 2.0 to 7.0. At pH 6.0 and 7.0, UO $_{2}$ $^{2+}$ was not reduced to U(IV) completely at the electrode potential above -0.8 V. Ultraviolet-visible spectroscopy and speciation calculation of UO $_{2}$ $^{2+}$ in citrate media indicated that uranium existed as a mainly UO $_{2}$ $^{2+}$ at pH 2-3, and a predominant species at pH 3-5 was [(UO $_{2}$ ) $_{2}$ Cit $_{2}$ ] $^{2-}$ . At pH 5-7, polymeric complexes were present. These findings suggest that the reduction of UO $_{2}$ $^{2+}$ is more difficult by polymerization of UO $_{2}$ $^{2+}$ with citric acid at higher pHs.

Journal Articles

Sorption of Eu(III) on in the presence of citric acid

Suzuki, Yoshinori; Nankawa, Takuya; Yoshida, Takahiro*; Ozaki, Takuo; Onuki, Toshihiko; Francis, A. J.*; Tsushima, Satoru*; Enokida, Yoichi*; Yamamoto, Ichiro*

Journal of Nuclear and Radiochemical Sciences, 6(1), p.91 - 93, 2005/07

https://doi.org/10.14494/jnrs2000.6.91

We studied the sorption of Eu(III) on Pseudomonas fluorescens in the absence and presence of citric acid by a batch method. The cells were placed in a solution containing 0.002 mM of Eu(III) and 0, 0.1, or 1 mM of citric acid at pH 3-9 for 5 hours. In the absence of citric acid, almost 100 % of Eu(III) was sorbed on P. fluorescens at pHs below 7; above 7, sorption decreased with an increase in pH. The time course of Eu(III) sorption on P. fluorescens showed that a fraction of it was desorbed into the solution at alkaline pHs, suggesting that the bacterium may release some exudates. With citric acid present, we found that at higher concentrations there was lower sorption of Eu(III), reflecting the formation of Eu(III)-citrate complexes competes with the Eu(III)-cell-surface complexes. This decrease in Eu(III) sorption was significant in alkaline pHs.

Journal Articles

Removal and recovery of uranium from solid wastes by supercritical carbon dioxide fluid leaching method

Meguro, Yoshihiro; Tomioka, Osamu; Imai, Tomoki*; Fujimoto, Shigeyuki*; Nakashima, Mikio; Yoshida, Zenko; Honda, Tadashi*; Koya, Fumio*; Kitamura, Nobu*; Wada, Ryutaro*; et al.

Proceedings of International Waste Management Symposium 2004 (WM '04) (CD-ROM), 8 Pages, 2004/03

Supercritical CO $_{2}$ fluid leaching (SFL) method using supercritical CO $_{2}$ fluid containing a complex of HNO $_{3}$ - tri-n-butyl phosphate (TBP) was applied to removal of uranium from radioactive solid wastes. Sea sands, incineration ashes and porous alumina bricks were employed as matrixes of simulated solid wastes. Real radioactive incineration ash wastes and firebrick wastes were also subjected to the SFL treatment. It was found that uranium could be efficiently removed from both of the simulated wastes and real wastes by the SFL method. The removal efficiency of uranium from the real waste was lower than that from the corresponding artificial waste. About 1 g and 35 mg of uranium were recovered from 10 g of the real ash waste and 37 g of the real firebrick waste, respectively.

Journal Articles

Recovery of alkali salt by supercritical fluid leaching method using carbon dioxide

Watanabe, Takeshi*; Tsushima, Satoru*; Yamamoto, Ichiro*; Tomioka, Osamu; Meguro, Yoshihiro; Nakashima, Mikio; Wada, Ryutaro*; Nagase, Yoshiyuki*; Fukuzato, Ryuichi*

Proceedings of 2nd International Symposium on Supercritical Fluid Technology for Energy and Environment Applications (Super Green 2003), p.363 - 366, 2004/00

Recovery of salts by supercritical fluid leaching (SFL) method using carbon dioxide was experimentally studied. It was confirmed that LiCl was recovered with a mixed fluid of carbon dioxide and methanol, and KCl and SrCl were recovered with a mixed fluid of carbon dioxide, methanol and crown ether. The influence of crown ether for KCl and SrCl extraction were found to increase in the order of 15-crown-5 (15C5) 18-crown-6 (18C6) dicychlohexyl-18-crown-6 (DC18C6). It is expected that other salts can be recovered selectively with a mixed fluid of carbon dioxide, methanol and suitable crown ether.

Journal Articles

Theoretical study of hydrolysis reactions of tetravalent thorium ion

Okamoto, Yasuharu*; Mochizuki, Yuji*; Tsushima, Satoru*

Chemical Physics Letters, 373(1-2), p.213 - 217, 2003/05

https://doi.org/10.1016/S0009-2614(03)00592-X

Times Cited Count：8 Percentile：24.96(Chemistry, Physical)

no abstracts in English

Journal Articles

On the electronic structures of Th $^{4+}$ and Ac $^{3+}$ hydrate models

Mochizuki, Yuji*; Tsushima, Satoru*

Chemical Physics Letters, 372(1-2), p.114 - 120, 2003/04

https://doi.org/10.1016/S0009-2614(03)00373-7

Times Cited Count：13 Percentile：39.19(Chemistry, Physical)

no abstracts in English

Oral presentation

Structural determination of neptunium species in aqueous solutions by EXAFS and quantum chemical calculations

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

no journal, ,

Neptunium (93Np) is one of the most problematic nuclides in the nuclear fuel reprocessing process and the following radioactive waste disposal because of its chemical similarity to the fissile nuclides of uranium (U) and plutonium (Pu). Proper understanding of the behavior of Np in the reprocessing process or in the migration process on the geological disposal of radioactive wastes requires vast fundamental information about the chemical properties of Np in solutions. In the present study, Np solution samples with different oxidation states are electrochemically prepared in aqueous perchlorate, nitrate, and carbonate solutions, and the complex structure of Np species in the sample solutions are determined by EXAFS spectroscopy and DFT calculations. The obtained results reveal the structural difference between different Np oxidation states, as well as the different coordination behavior in each solution system.

Oral presentation

Structural determination of neptunium species in aqueous solutions by EXAFS and quantum chemical calculations

Ikeda, Atsushi; Yaita, Tsuyoshi; Okamoto, Yoshihiro; Shiwaku, Hideaki; Tsushima, Satoru*; Hennig, C.*

no journal, ,

Neptunium (93Np) is one of the most problematic nuclides in the nuclear fuel reprocessing process and the following radioactive waste disposal. Proper understanding of the Np behavior in the reprocessing process or in the migration process on the geological disposal of radioactive wastes requires vast fundamental information about the chemical properties of Np in solutions. In the present study, Np solution samples with different oxidation states are electrochemically prepared in various aqueous solutions, and the complex structure of Np species in the sample solutions are determined by EXAFS spectroscopy, partly with the help of DFT calculations.

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.