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Journal Articles

High spectral resolution of diode laser absorption spectroscopy for isotope analysis using a supersonic plasma jet

Kuwahara, Akira; Aiba, Yasuaki*; Yamasaki, Shinya*; Nankawa, Takuya; Matsui, Makoto*

Journal of Analytical Atomic Spectrometry, 33(7), p.1150 - 1153, 2018/07

 Percentile:100(Chemistry, Analytical)

Although high-temperature plasma sources have been used for direct isotope analysis of solid samples, the spectral resolution of diode laser absorption spectroscopy in high-temperature plasma is limited by the Doppler broadening of atomic absorption lines. Thus, a decrease in translational temperature is necessary to enhance the spectral resolution and distinguish isotope shifts due to mass number. In this study, a supersonic plasma wind tunnel, also called an arc-jet plasma wind tunnel, was used to enhance spectral resolution drastically, and a demonstration was carried out using natural stable xenon isotopes. As a result, the temperature was found to be about 180 K and the spectral resolution was about one order of magnitude higher than that of the conventional high-temperature source. Additionally, the method proposed herein was verified by using two xenon isotopes.

Journal Articles

Development of an isotope analysis method based on diode laser absorption spectroscopy using an arc-jet plasma wind tunnel

Kuwahara, Akira; Aiba, Yasuaki*; Nankawa, Takuya; Matsui, Makoto*

Journal of Analytical Atomic Spectrometry, 33(5), p.893 - 896, 2018/05

 Times Cited Count:1 Percentile:47.42(Chemistry, Analytical)

no abstracts in English

Journal Articles

Redox behavior of uranium(VI) adsorbed onto a phosphate-modified indium tin oxide electrode

Suzuki, Yoshinori*; Nankawa, Takuya; Onuki, Toshihiko

Chemistry Letters, 42(8), p.888 - 890, 2013/08

 Percentile:100(Chemistry, Multidisciplinary)

no abstracts in English

Journal Articles

Selective removal of cesium ions from wastewater using copper hexacyanoferrate nanofilms in an electrochemical system

Chen, R.*; Tanaka, Hisashi*; Kawamoto, Toru*; Asai, Miyuki*; Fukushima, Chikako*; Na, H.*; Kurihara, Masato*; Watanabe, Masayuki; Arisaka, Makoto; Nankawa, Takuya

Electrochimica Acta, 87, p.119 - 125, 2013/01

 Times Cited Count:62 Percentile:5.36(Electrochemistry)

A novel electrochemical adsorption system using a nanoparticle film of copper (II) hexacyanoferrate (III) was proposed for selectively removing cesium from wastewater. This system can be used for cesium separation without extra chemical reagents or any filtration treatment. Cesium uptake and elution can be simply controlled by switching the applied potentials between anodes and cathodes. Data from batch kinetic studies well fitted the intraparticle diffusion equation, reflecting a two-step process: a steepest ascent portion followed by a plateau extending to the equilibrium. The effective cesium removal with a high distribution coefficient ($$K$$$$_{d}$$ $$>$$ 5$$times$$10$$^{5}$$ mL/g) can be adopted in a large pH range from 0.3 to 9.2, and in the presence of several diverse coexisting alkaline cations, suggesting it can be taken as a promising technology for actual nuclear wastewater treatment.

Journal Articles

Preparation of a film of copper hexacyanoferrate nanoparticles for electrochemical removal of cesium from radioactive wastewater

Chen, R.*; Tanaka, Hisashi*; Kawamoto, Toru*; Asai, Miyuki*; Fukushima, Chikako*; Kurihara, Masato*; Watanabe, Masayuki; Arisaka, Makoto; Nankawa, Takuya

Electrochemistry Communications, 25, p.23 - 25, 2012/11

 Times Cited Count:34 Percentile:18.11(Electrochemistry)

We first synthesized water-dispersed nanoparticle copper hexacyanoferrate (CuHCF) ink and then coated its nanoparticles on electrodes to electrochemically remove cesium from wastewater. Cesium uptake and elution can be controlled by switching the potentials between anodes and cathodes. Effective cesium removal can be adopted in a large pH range from 0.2 to 8.9, and in the presence of several diverse coexisting alkaline cations, suggesting that it can be taken as a promising technology for actual radioactive wastewater treatment. The prepared CuHCF nanoparticles can be simply and uniformly coated on electrodes by wet process like conventional printing methods, so any sizes or patterns are feasible at low cost, which indicated the potential as a promising sorption electrode of large size in the columns for sequential removal and recycle of Cs from wastewater.

Journal Articles

Yeast genes involved in uranium tolerance and uranium accumulation; A Functional screening using the nonessential gene deletion collection

Sakamoto, Fuminori; Nankawa, Takuya; Onuki, Toshihiko; Fujii, Tsutomu*; Iefuji, Haruyuki*

Geomicrobiology Journal, 29(5), p.470 - 476, 2012/05

 Times Cited Count:5 Percentile:76.11(Environmental Sciences)

We screened 4908 non-essential gene deletion mutant yeast strains for uranium sensitivity and low accumulation by growth in agar medium containing uranium. All mutant strains grew successfully on agar media containing 0 or 0.5 mM uranium for one week at 30 centigrade. Thirteen strains with single gene deletions showed reduced growth in the agar medium containing 0.5 mM uranium and were identified as uranium-sensitive mutant strains. The phosphate transporter genes of PHO86, PHO84, PHO2, and PHO87 were among the deleted genes in the uranium-sensitive mutant strains, suggesting that genes concerned with phosphate transport contribute to uranium tolerance. Seventeen single-deletion strains showed lower uranium accumulation than the wild-type after exposure to agar medium containing 0.5 mM uranium, and were identified as mutant strains with low uranium accumulation.

Journal Articles

Redox behavior of Ce(IV)/Ce(III) in the presence of nitrilotriacetic acid; A Surrogate study for An(IV)/An(III) redox behavior

Suzuki, Yoshinori*; Nankawa, Takuya; Francis, A. J.*; Onuki, Toshihiko

Radiochimica Acta, 98(7), p.397 - 402, 2010/07

 Times Cited Count:12 Percentile:26.04(Chemistry, Inorganic & Nuclear)

no abstracts in English

Journal Articles

Association of actinides with microorganisms and clay; Implications for radionuclide migration from waste-repository sites

Onuki, Toshihiko; Kozai, Naofumi; Sakamoto, Fuminori; Ozaki, Takuo; Nankawa, Takuya; Suzuki, Yoshinori; Francis, A. J.*

Geomicrobiology Journal, 27(3), p.225 - 230, 2010/04

 Times Cited Count:13 Percentile:76.04(Environmental Sciences)

The recent research results on the interation of heavy-elements and microorganisms are shown. (1) Adsorption of Pu(IV), Th(IV) and Eu(III)-DFO complexes on bacteria, (2) Biodegradation of Eu(III) in the presence of malic acids.

Journal Articles

In situ observation of reductive deposition of uranium on an electrode/electrolyte interface by optical waveguide spectroscopy

Nankawa, Takuya; Suzuki, Yoshinori; Onuki, Toshihiko

Chemistry Letters, 38(11), p.1090 - 1091, 2009/11

 Times Cited Count:1 Percentile:90.61(Chemistry, Multidisciplinary)

We report the first in situ and real-time observation of UV-vis absorption spectra of uranium electrodeposited on indium-tin-oxide electrodes by slab optical waveguide spectroscopy. An absorption peak around 670 nm was distinguished after a 30-min holding period at -0.2 V (vs. Ag/AgCl). X-ray absorption near edge structure spectroscopy confirmed the presence of uranium(IV) in the uranium electrodeposited on the ITO electrode.

Journal Articles

Modeling of the interaction of Pu(VI) with the mixture of microorganism and clay

Onuki, Toshihiko; Yoshida, Takahiro*; Ozaki, Takuo; Kozai, Naofumi; Sakamoto, Fuminori; Nankawa, Takuya; Suzuki, Yoshinori; Francis, A. J.*

Journal of Nuclear Science and Technology, 46(1), p.55 - 59, 2009/01

Model analysis of the transformation of Pu(VI) in a mixture of a common soil bacterium, Bacillus subtilis, and kaolinite clay was carried out. When we assumed in the model analysis that reduction rate of Pu(V) to Pu(IV) was higher on B. subtilis than on kaolinite, the estimated fractions of Pu in the solution and in the mixture, oxidation states of Pu in the solution and in the mixture were in good agreement with the measured ones. On the contrary, assumption that reduction rate of Pu(V) to Pu(IV) was the same on kaolinite as on ${it B. subtilis}$ gave wrong prediction of Pu association with the mixture. These results strongly suggested the electron transfer from the bacteria to Pu(V) on the bacterial cell to be reduced to Pu(IV) during the accumulation of Pu(VI) to the mixture.

Journal Articles

Concurrent transformation of Ce(III) and formation of biogenic manganese oxides

Onuki, Toshihiko; Ozaki, Takuo; Kozai, Naofumi; Nankawa, Takuya; Sakamoto, Fuminori; Sakai, Takuro; Suzuki, Yoshinori; Francis, A. J.*

Chemical Geology, 253(1-2), p.23 - 29, 2008/07

 Times Cited Count:20 Percentile:43.93(Geochemistry & Geophysics)

We examined the changes in the chemical states of Ce(III) during the formation of manganese oxide occasioned by Mn(II)-oxidizing bacteria. The oxidation states of Ce and Mn then were measured by X-ray Absorption Near Edge Structure (XANES). We also determined the elemental distributions in the bacteria and precipitates by Scanning-Proton Induced X-ray Emission (S-PIXE). We found that the precipitation of Ce is preceded by its accumulation by the bacterium, followed by its oxidization to Ce(IV) by the Mn(III, IV)-containing precipitates that the bacteria generate.

Journal Articles

Sorption of U(VI) on the 4-mercaptopyridine self-assembled monolayer

Nankawa, Takuya; Suzuki, Yoshinori; Ozaki, Takuo; Francis, A. J.; Onuki, Toshihiko

Journal of Nuclear Science and Technology, 45(3), p.251 - 256, 2008/03

 Times Cited Count:3 Percentile:70.64(Nuclear Science & Technology)

Sorption of U(VI) on the 4-mercaptopyridine self-assembled-monolayer (4-PyS-SAM) on Au(111) was studied by cyclic voltammetry. Cyclic voltammograms (CV) of the 4-PyS-SAM working electrode was obtained by contact with 1 mM UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$ solution, 1 mM UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$ and 50 mM acetic acid solution, or 1 mM UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$ and 50 mM oxalic acid solution for 6 h at pH 4. Reduction current of uranium(VI) to U(V) was detected in the CV. The CV of the U(VI) associated 4-PyS-SAM after transporting to U(VI) free 0.1 M NaClO4 solution showed that the reduction current was detected in the cases of UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$ and U(VI)-acetate, but not in the case of U(VI)-oxalate solutions, indicating that U(VI) was adsorbed on the 4-PyS-SAM from the UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$ and U(VI)-acetate solutions, but not from U(VI)-oxalate solution. These results suggests that stability of U(VI)-4-PyS-SAM is not so high that U(VI)-4-PyS-SAM cannot be formed in the presence of 50 mM oxalate.

Journal Articles

Protein expression of ${it Saccharomyces cerevisiae}$ in response to uranium exposure

Sakamoto, Fuminori; Nankawa, Takuya; Kozai, Naofumi; Fujii, Tsutomu*; Iefuji, Haruyuki*; Francis, A. J.; Onuki, Toshihiko

Journal of Nuclear and Radiochemical Sciences, 8(2), p.133 - 136, 2007/10

Protein expression of ${it Saccharomyces cerevisiae}$ grown in the medium containing $$^{238}$$U(VI) and $$^{233}$$U(VI) was examined by two-dimensional gel electrophoresis. ${it S. cerevisiae}$ of BY4743 was grown in medium containing $$^{238}$$U of 0, 2.0, and 5.0 $$times$$ 10$$^{-4}$$ M or $$^{233}$$U of 2.5 $$times$$ 10$$^{-6}$$ (radioactivity was higher by 350 times than 2.0 $$times$$ 10$$^{-4}$$ M $$^{238}$$U) and 5.0 $$times$$ 10$$^{-6}$$ M for 112 h at 30$$^{circ}$$C. The growths of the yeast grown in the above media were in the following order: control $$>$$ 2.5 $$times$$ 10$$^{-6}$$ M $$^{233}$$U $$>$$ 2.0 $$times$$ 10$$^{-4}$$ M $$^{238}$$U $$>$$ 5.0 $$times$$ 10$$^{-6}$$ M $$^{233}$$U $$>$$ 5.0 $$times$$ 10$$^{-4}$$ M $$^{238}$$U. This result indicated that not only radiological but also chemical effect of U reduced the growth of the yeast. The concentrations of U in the medium containing $$^{238}$$U or $$^{233}$$U decreased, suggesting U accumulation by the yeast cells. The 2-D gel electrophoresis analysis showed the appearance of several spots after exposure to $$^{238}$$U or to $$^{233}$$U but not in the control containing no uranium. These results show that the yeast cells exposed to U express several specific proteins.

Journal Articles

Electrochemical studies on uranium in the presence of organic acids

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

Journal of Nuclear Science and Technology, 44(9), p.1227 - 1232, 2007/09

 Times Cited Count:9 Percentile:37.95(Nuclear Science & Technology)

We examined electrochemical redox reactions of UO$$_{2}$$$$^{2+}$$ in organic acid (oxalic, malonic, succinic, adipic, L-malic, and L-tartaric acids) solutions using cyclic voltammetry. A redox reaction of UO$$_{2}$$$$^{2+}$$/UO$$_{2}$$$$^{+}$$ and an oxidation reaction of U(IV) were observed. The peak potentials of the UO$$_{2}$$$$^{2+}$$ reduction showed a good linear relationship with the log of the stability constants of 1:1 UO$$_{2}$$$$^{2+}$$-organic complexes. We also revealed the redox reactions of UO$$_{2}$$$$^{2+}$$ in the presence of malonic or oxalic acids between pH 1 and 6.

Journal Articles

Chemical speciation and association of plutonium with bacteria, kaolinite clay, and their mixture

Onuki, Toshihiko; Yoshida, Takahiro*; Ozaki, Takuo; Kozai, Naofumi; Sakamoto, Fuminori; Nankawa, Takuya; Suzuki, Yoshinori*; Francis, A. J.

Environmental Science & Technology, 41(9), p.3134 - 3139, 2007/05

 Times Cited Count:27 Percentile:38.21(Engineering, Environmental)

We investigated the interactions of Pu(VI) with Bacillus subtilis, kaolinite clay, and a mixture of the two to determine and delineate the role of the microbes in regulating the environmental mobility of Pu. The amount of Pu sorbed by B. subtilis increased with time, but had not reached equilibrium in 48 h, whereas equilibrium was attained in kaolinite within 8 h. After 48 h, the oxidation state of Pu in the solutions exposed to B. subtilis and the mixture had changed to Pu(V), whereas the oxidation state of Pu associated with B. subtilis and the mixture was Pu(IV). In contrast, there was no change in the oxidation state of Pu in the solution or on kaolinite after exposure to Pu(VI). SEM-EDS analysis indicated that most of the Pu in the mixture was associated with B. subtilis. These results suggest that Pu(IV) is preferably sorbed to bacterial cells in the mixture, and that Pu(VI) is reduced to Pu(V) and Pu(IV).

Journal Articles

Control of coordination and luminescence properties of lanthanide complexes using octadentate oligopyridine-amine ligands

Wada, Atsushi*; Watanabe, Masayuki; Yamanoi, Yoshinori*; Nankawa, Takuya; Namiki, Kosuke*; Yamasaki, Mikio*; Murata, Masaki*; Nishihara, Hiroshi*

Bulletin of the Chemical Society of Japan, 80(2), p.335 - 345, 2007/02

 Times Cited Count:18 Percentile:43.6(Chemistry, Multidisciplinary)

Lanthanide complexes with linear and cyclic octadentate oligopyridine-amine ligands were synthesized, and their molecular structures were determined by single-crystal X-ray crystallography. All of the complexes had a distorted capped square antiprism (CSAP) geometry, and the coordination environments of lanthanide complexes were more distortedfor the complexes with the linear ligand than those with the cyclic ligand. The Eu$$^{3+}$$ complexes with the linear ligand showed more intense emissions, which were attributed to the $$^{5}$$D$$_{0}$$ $$rightarrow$$ $$^{7}$$F$$_{2}$$ transition, than the complex withthe cyclic ligand in acetonitrile, which can be attributed to the distortion in the coordination environments. These results indicate that the coordination environments of lanthanide complexes, and thus the luminescence properties, can be controlled by tuning the geometrical structures of polydentate ligands.

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

 Times Cited Count:15 Percentile:22.32(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

Degradation of Eu(III)-malic acid complexes by $$Pseudomonas fluorescens$$

Nankawa, Takuya; Suzuki, Yoshinori*; Ozaki, Takuo; Onuki, Toshihiko; Francis, A. J.*

Journal of Alloys and Compounds, 408-412, p.1329 - 1333, 2006/02

 Times Cited Count:1 Percentile:84.44(Chemistry, Physical)

We studied the biodegradation of Eu(III)-malic acid complexes by $$Pseudomonas fluorescens$$. Ten milimolar Malic acid was degraded in the absence and in the presence of Eu(III) of 0.05, 0.1, and 0.2 mM. The degradation rate of malic acid increased with decreasing the ratios of Eu(III) to malic acid. These results suggest that the toxicity of Eu(III) can be masked through its complexation with malic acid. The degradation of malic acid was followed by the production of unidentified metabolites which were associated with Eu(III). One of the unidentified organic acids was analysed to be pyruvic acid. Our findings suggest that metabolites can influence the environmental behavior of Eu(III) by biologically transformed through subsequent complexation with Eu(III).

Journal Articles

Interactions of rare earth elements with bacteria and organic ligands

Ozaki, Takuo; Suzuki, Yoshinori*; Nankawa, Takuya; Yoshida, Takahiro; Onuki, Toshihiko; Kimura, Takaumi; Francis, A. J.*

Journal of Alloys and Compounds, 408-412, p.1334 - 1338, 2006/02

 Times Cited Count:33 Percentile:12.43(Chemistry, Physical)

We investigated the interactions of Eu(III) with the common soil bacterium Pseudomonas fluorescens and organic ligands, such as malic acid, citric acid, and a siderophore (DFO). Malic acid formed complexes with Eu(III), but degradation of malic acid was observed when the ratio of malic acid to Eu(III) was high. Citric acid formed a stoichiometric complex with Eu(III) that was not degraded by P. fluorescens. Adsorption of Eu(III) from the DFO complex occurred as a free ion dissociated from DFO and not as the Eu(III)-DFO complex. Time-resolved laser-induced fluorescence spectroscopy analysis showed that adsorption of Eu(III) on P. fluorescens was through a multidentate and predominantly inner-spherical coordination.

Journal Articles

A Continuous flow system for in-situ XANES measurements of change in oxidation state of Ce(III) to Ce(IV)

Onuki, Toshihiko; Yoshida, Takahiro*; Nankawa, Takuya; Ozaki, Takuo; Kozai, Naofumi; Sakamoto, Fuminori; Suzuki, Yoshinori*; Francis, A. J.*

Journal of Nuclear and Radiochemical Sciences, 6(1), p.65 - 67, 2005/07

no abstracts in English

77 (Records 1-20 displayed on this page)