Katsuya Teshima

Shinshu University, Shonai, Nagano, Japan

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Publications (91)190.47 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Graphene monoliths made from graphene oxide colloids by unidirectional freeze-drying method were activated by typical activation processes of CO2 activation, chemical activation using ZnCl2 or H3PO4, and KOH activation. The porosity development of graphene monolith markedly depends on the activation method. The monoliths with highest surface area are obtained by the KOH activation method; only the KOH activation is effective for production of the graphene monolith of which surface area is in the range of 1760–2150 m2 g−1. The mechanism of the porosity development by KOH activation method is proposed. This work provides a promising route for the bottom-up design of pore width-tunable nanoporous carbons.
    Carbon 09/2014; 76:220–231. · 6.16 Impact Factor
  • Kunio Yubuta, Katsuya Teshima, Shuji Oishi
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    ABSTRACT: The structure of Nb2O5 nanotubes was studied by electron diffraction and high-resolution transmission electron microscopy (HRTEM). The nanotubes were prepared from highly crystalline-layered K4Nb6O17 crystals grown from a KCl flux using the intercalating and exfoliating techniques. Nanotubes have a length of about 200 nm and a diameter of 20 nm. The observed electron diffraction patterns revealed that the nanotubes have a helical structure with the basal plane of (010) and the tube-axis parallel to the [201] direction. Their basal plane corresponds to the (010) plane of the layered K4Nb6O17 crystals. The helical lattice plane was directly observed by a Fourier filtered HRTEM image. Copyright © 2014 John Wiley & Sons, Ltd.
    Surface and Interface Analysis 04/2014; · 1.39 Impact Factor
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    ABSTRACT: Higher performance active materials containing cathodes have been strongly required for the achievement of advanced lithium-ion rechargeable batteries. We report the formation of a densely packed and idiomorphic LiCoO2 crystal layer directly on a substrate surface using flux coating with a LiNO3–LiOH mixed flux and their applications as an additive-free cathode to enhance gravimetric energy density per single cell as well as durability. The formation mechanism of LiCoO2 nanocrystals from high temperature melt of the mixed flux was controlled under evolution selection growth, driven by supersaturation. The as-grown crystals formed a petal-shape with well-developed {001} faces. After annealing treatment, the crystal shape transformed into hexagonal plates with vertical orientation. The hexagonal plate-shaped crystal arrays were identified to be homogeneous LiCoO2 having a rhombohedral crystal system. Their lattice parameters were a = 0.2784 and c = 1.4248 nm, and the Li/Co ratio in the crystals was 1.00. Furthermore, transmission electron microscopic images and selected area electron diffraction patterns revealed that the interface between the crystal layer and the substrate was smoothly connected and free of impurities. In fact, the LiCoO2 nanoplate layer exhibited desirable properties such as a large discharge capacity close to its theoretical value, higher rate performance, and high cyclability over 500 cycles with no assistance of additional electroconductive materials and binders, meaning that the interfaces provide seamless charge transportation pathways.
    Crystal Growth & Design 03/2014; 14(4):1882–1887. · 4.69 Impact Factor
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    ABSTRACT: Fluorescein-dispersing titania gel films were prepared by the acid-catalyzed sol-gel reaction using a titanium alkoxide solution containing fluorescein. The molecular forms of fluorescein in the films, depending on its acid-base equilibria, and the complex formation and photoinduced electron transfer process between the dye and titania surface were investigated by fluorescence and photoelectric measurements. The titanium species were coordinated to the carboxylate and phenolate-like groups of the fluorescein species. The quantum efficiencies of the fluorescence quenching and photoelectric conversion were higher upon excitation of the dianion species interacting with the titania, i.e., the dye-titania complex. This result indicated that the dianion form was the most favorable for formation of the dye-titania complex exhibiting the highest electron transfer efficiency. Using nitric acid as the catalyst, the titania surface bonded to the fluorescein instead of the adsorbed nitrate ion during the steam treatment. The dye-titania complex formation played an important role in the electron injection from the dye to the titania conduction band. This article is protected by copyright. All rights reserved.
    Photochemistry and Photobiology 02/2014; · 2.29 Impact Factor
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    ABSTRACT: Photocatalytic Nb2O5 nanocrystal layers were successfully synthesized using NbOx nanosheets obtained from layered K4Nb6O17 crystals. First, idiomorphic K4Nb6O17 crystals were grown using the KCl flux method, and then a two-step process involving proton exchange and exfoliation was carried out in order to make the nanosheets. Next, the rectangular nanosheets were mixed with polyethylene glycol, water and ethanol to prepare a nanosheet paste, and the paste was then evenly spin-cast on silica glass. Upon heating, decomposition and evaporation of the solvents yielded transparent, colorless nanocrystal layers with good adhesion. During the heating process, some nanosheets rolled up into nanotubes; therefore, nanocrystal layers consisting of both nanosheets and nanotubes were fabricated. The nanocrystal layers exhibited photocatalytic activity for the photodegradation of organosilane thin films under UV light irradiation. The organosilane thin films were photocatalytically decomposed and that the surfaces were converted from hydrophobic to ultrahydrophilic. Furthermore, micropatterned nanocrystal layer was readily fabricated using hydrophobic/hydrophilic template.
    Applied Surface Science 09/2013; · 2.54 Impact Factor
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    ABSTRACT: Well-aligned honeycomb-designed layers of potassium tungstate (K0.33WO3.165) were successfully fabricated by spray deposition and microsphere lithography using polystyrene (PS) colloidal crystals as templates. A densely packed monolayer of monodisperse PS microspheres was formed on a silica glass surface, using the Langmuir–Blodgett thin film technique. Subsequently, a (NH4)10W12O41·5H2O-KCl aqueous solution was sprayed as a micromist on the PS templates. While the K0.33WO3.165 crystal layers were synthesized by chemical reaction between W and K sources during the heating, the PS templates were thermally decomposed, generating an inverse opal surface structure where the interstitial space of the densely hexagonal packed PS microspheres had been. Numerous hexagonal rodlike crystals were grown on the honeycomb-designed layer of K0.33WO3.165. X-ray diffraction analysis, energy-dispersive X-ray spectroscopy analyses, and X-ray photoelectron spectroscopy were performed to analyze the combined one-dimensional and three-dimensional honeycomb-designed structure.
    Crystal Growth & Design 07/2013; 13(8):3294–3298. · 4.69 Impact Factor
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    ABSTRACT: Dye-dispersing titania electrodes were prepared from the dye-containing titanium alkoxide sols by a room temperature sol–gel process and steam treatment at 110 °C. The spectroscopic and photoelectric conversion properties of the electrodes were investigated in order to clarify the influences of the dye dispersion and the co-dispersion of the two dyes on the electron transfer process. The fluorescein and eosin Y molecules were dispersed into the titania as their monomers. The shapes of the photocurrent action spectra of the fluorescein and/or eosin Y-dispersing titania electrodes corresponded well to those of their absorption spectra because the excited electrons in the dyes were directly injected into the titania conduction band without any interaction between the dye molecules, such as energy transfer. This result indicated that the dye molecules were separately encapsulated in the pores between the titania nanoparticles and tightly adsorbed or bonded to the titania particle surface. The internal quantum efficiency of the photoelectric conversion was higher than that of the conventional dye-adsorbing titania electrodes in which the dye molecules were easily aggregated and thus deactivated by the energy transfer. The co-dispersion of the two dyes on the titania surface allowed effective extension of the visible light region for the photoelectric conversion.
    Catal. Sci. Technol. 05/2013; 3(6):1512-1519.
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    ABSTRACT: The growth of NaTaO3 crystals through the reaction between NaNO3 and a Ta substrate was directly observed using in-situ laser microscopy and in-situ X-ray diffraction. Voids and creases were first produced at 430 °C and then NaTaO3 crystals grew at 440 °C in a moment. Because the NaTaO3 crystals had formed during heating, the driving force for crystal growth was concluded to be the evaporation of NaNO3.
    CrystEngComm 04/2013; 15(20):4058-4061. · 3.88 Impact Factor
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    ABSTRACT: The International Conference on Thin Films is the most established conference for all researchers and persons interested in thin films and coatings. It is one of the tri-annual conference series endorsed and co-organized by the Thin Film Division of the International Union for Vacuum Science, Technique and Applications (IUVSTA), a union of national member societies whose role is to stimulate international collaboration in the fields of vacuum science, techniques and applications and related multi-disciplinary topics including solid-vacuum and other interfaces. The 15th International Conference on Thin Films (ICTF-15) is organized by The Vacuum Society of Japan (VSJ) and held at Kyoto TERRSA in Kyoto, Japan on 8-11 November 2011, following the 14th International Conference on Thin Films (ICTF-14), which was held in Ghent, Belgium in 2008. Thin films and coatings are daily becoming increasingly important in the fields of various industries. This International Conference provides a multi-disciplinary forum for recent advances in basic research, development and applications of thin films and coatings. This conference will present a unique opportunity for researchers, engineers and managers to acquire new knowledge of thin films and coatings. We hope that our understanding on thin films and coatings will be deepened through this conference. The conference site, 'Kyoto TERRSA' is located in the historical heart of the old capital Kyoto. Kyoto is an ancient city with a 1200-year history. It was established as Japan's capital under the name 'Heian-kyo' in the year 794. Although many transformations have taken place over the years, Kyoto has always embraced the most advanced standards of the times. It has greatly contributed to the nation's industrial, economic and cultural development. The dauntless spirit of leadership of Kyoto's past as a capital city is still felt here today. Kyoto also preserves the beloved examples of its culture as testimonials of time. This is shown in the ancient temples and shrines, as well as private houses, which are built in styles unique to Kyoto. Furthermore, many festivals, ceremonies and traditional activities reveal the will of this city to convey and develop its 1200-year-old culture. Participants of the conference will also be able to see many world heritage sites in the city. Moreover, November is the best time of year to visit Kyoto. We hope you will enjoy Kyoto very much. We would like to offer our thanks for all the contributions from the members of the International Advisory Committee and Organizing Committee, Symposium Chairs, the Secretary General, the Thin Film Division of IUVSTA (chair: Professor Dr Alberto Tagliaferro), IUVSTA, VSJ and other cooperating societies, and to all of the supporting organizations and enterprises. We would also like to express our thanks to all of the participants, secretariat members and members of the supporting staff. I am very pleased to welcome you to ICTF-15 and Kyoto! Director Professor Dr Osamu Takai Chairperson of ICTF-15 EcoTopia Science Institute, and Department of Materials, Physics and Energy Engineering Graduate School of Engineering Nagoya University Japan
    Journal of Physics Conference Series 03/2013; 417(1):1001-.
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    ABSTRACT: High-quality upconversion YO1–xF1+2x:Ln (Ln = Yb, Er, Ho, and Tm) layers with good adhesion, comprising densely packed, plate-shaped idiomorphic crystals, were directly grown on stainless steel (SUS) substrates by flux coating. The LiNO3–KNO3 flux effectively promoted crystal growth. Additionally, the near-infrared-to-visible (NIR-vis) upconversion fluorescence properties of the YO1–xF1+2x:Ln crystal layers could be tuned by varying the type of dopant (Ln element). YO1–xF1+2x:Yb,Er, YO1–xF1+2x:Yb,Ho, and YO1–xF1+2x:Yb,Tm crystal layers showed red, green, and blue fluorescence, respectively, under 980 nm laser irradiation.
    Crystal Growth & Design 02/2013; 13(3):1187–1192. · 4.69 Impact Factor
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    ABSTRACT: High-quality, idiomorphic, single-phase Li5La3Nb2O12 crystals were successfully grown using a LiOH flux cooling method at the relatively low temperature of 500 °C at a solute concentration of 5 mol %. The grown Li5La3Nb2O12 crystals had polyhedral shapes with well-developed, flat {211} and {110} faces. Their shapes were relatively uniform, and the average crystal size was approximately 59.2 μm. No aggregation was observed in scanning electron microscopy images. The high crystallinity of the Li5La3Nb2O12 crystals was confirmed by transmission electron microscopy images. Their lattice parameter was determined from the X-ray diffraction pattern to be a = 1.281 nm, which is consistent with the literature value (a = 1.282 nm). Furthermore, the crystal phase, form, size, and crystallinity of the flux-grown Li5La3Nb2O12 crystals were obviously dependent on the growth conditions including the solute concentration and holding temperature.
    Crystal Growth & Design 01/2013; 13(2):479–484. · 4.69 Impact Factor
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    ABSTRACT: High-quality nano-/microtextured NaTaO3 crystal layers were successfully fabricated on Ta substrates at a relatively low temperature using molten NaNO3 as the starting material. Ta substrates coated with an aqueous NaNO3 solution were heated at 500 °C in an infrared heating furnace, whereupon Ta reacted with NaNO3 (which acted as both the Na source and the flux) to afford a layer of densely packed cubic NaTaO3 crystals that adhered readily onto the substrate. Nitridation of the NaTaO3 crystal layer by heating at 850 °C under an NH3 flow yielded a Ta3N5 crystal layer. The crystals retained their original size and shape but became highly porous after nitridation. TEM observations clearly indicated that the porous cubic crystals consisted of highly crystalline nanoparticles.
    CrystEngComm 10/2012; 14(21):7178-7183. · 3.88 Impact Factor
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    ABSTRACT: Decrease of electric resistance during light-illumination was observed in ZnO films prepared by a low-temperature (< 100 °C) wet-chemical process. The electric resistance was measured by 2-terminal method, and decreased from 2 M to 200 by UV illumination for 12 h. The decrease of the resistance was strongly affected by the light wavelength, showing that the ZnO film illuminated by the light with shorter wavelength (365 nm) had lower electric resistance compared to the others (380, and 420 nm). In contrast, light with wavelength of 365 nm were more effective to maintain the resistance compared to that with wavelength of 325 nm. It indicated that the penetration depth of the light in the films were also important to decrease the resistance of the films.
    Journal of Flux Growth. 09/2012; 7:55-59.
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    ABSTRACT: Idiomorphic, one-dimensional (1-D), and high-quality hydroxyapatite (HAp) nanocrystals were successfully, directly, and densely grown on a Ti substrate at the relatively low temperature of 300 °C using a KNO3–LiNO3 flux coating method. The grown HAp crystals have a 1-D shape with a very high aspect ratio (much larger than 100) and an average size of 3250 × 25 nm (length × width). The ultralong 1-D crystals grown at 300 °C were identified as highly crystalline HAp by their X-ray diffraction (XRD) patterns, which clearly displayed the four characteristic lines of HAp between 31.5° and 34.5°. Additionally, high-resolution transmission electron microscopy (HRTEM) images demonstrated that these ultralong whiskers were high-quality because point and line defects were not observed. From the energy-dispersive X-ray spectroscopy (EDS) analysis, major components were homogeneously distributed in the HAp whiskers. In addition, the effects of holding temperature and starting composition on the forms and average sizes of the grown HAp whiskers were investigated.
    Crystal Growth & Design 08/2012; 12(10):4890–4896. · 4.69 Impact Factor
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    ABSTRACT: Well-formed, highly crystalline potassium titanate whiskers were successfully grown by the KCl flux cooling method at a holding temperature of 800 °C using metallic titanium materials. Of primary importance were the metallic Ti spheres and potassium chloride powders that were used as the starting materials for growth of the titanate whiskers. Ultralong K2Ti6O13 whiskers grew radially from the center of the Ti spheres by our flux technique. Cross-sectional SEM images demonstrate that the ultralong whiskers were grown on the TiO2 crystal layer, and the whisker spheres had a bilayer structure that was hollow in the center. When Ti powders were used as the starting material, spherical aggregation of K2Ti6O13 and K2Ti4O9 whiskers occurred. The product structures were different from those obtained from metallic Ti spheres. Based on SEM, EDS and XRD, the formation mechanism of the ultralong whiskers was also discussed. Furthermore, the photocatalytic activity of the whiskers was confirmed by trichloroethylene degradation under ultraviolet light irradiation.
    CrystEngComm 05/2012; 14(12):4176-4180. · 3.88 Impact Factor
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    ABSTRACT: Amorphous dye-containing titania gel films were prepared on ITO electrodes coated with a crystalline titania foundation from titanium alkoxide sols containing a dye at room temperature. Photoinduced electron transport in the amorphous titania gel film was investigated by spectroscopic and photovoltaic measurements. Influences of the structure and morphology of the multilayered film on the photoelectron transport and electrically conductive properties were discussed. The photocurrent was observed from only the layer contacting the crystalline titania foundation. The electron transport from the amorphous upper layers was limited. Steam treatment of the electrodes improved the electron transport due to crystallization of the amorphous titania to anatase accompanied by enhancement of its electrical conductivity. The efficiency of the dye-sensitized electron transport in the steam-treated titania film was close to that of the anatase film prepared by heating at 773 K. The dye-containing titania layers functioned as efficient sensitizers.
    RSC Advances 05/2012; 2(10):4258-4267. · 3.71 Impact Factor
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    ABSTRACT: Highly efficient water oxidation utilizing visible photons of up to 600 nm is a crucial step in artificial photosynthesis. Here we present a highly active photocatalyst for visible-light-driven water oxidation, consisting of single-crystalline meso- and macroporous LaTiO(2)N (LTON) with a band gap of 2.1 eV, and earth-abundasnt cobalt oxide (CoO(x)) as a cocatalyst. The optimized CoO(x)/LTON had a high quantum efficiency of 27.1 ± 2.6% at 440 nm, which substantially exceeds the values reported for previous particulate photocatalysts with a 600-nm absorption edge.
    Journal of the American Chemical Society 05/2012; 134(20):8348-51. · 10.68 Impact Factor
  • Hiromasa Nishikiori, Katsuya Teshima, Tsuneo Fujii
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    ABSTRACT: Spironaphthoxazine (SNO) and three metal ions, Mg(2+), Zn(2+), and Al(3+), were dispersed in silica gels by the sol-gel method. The chelation ability of SNO with the metal ions in silica gels was investigated by measuring the fluorescence spectra and was compared to that of 8-hydroxyquinoline (8-HQ) in ethanol and silica gels. A merocyanine-type isomer photoderived from SNO as well as 8-HQ easily formed complexes of the metal ions in the order of Al(3+), Zn(2+), and Mg(2+) because the coordination ability of the metal ions to such ligands depended on their electron affinity. The changes in the fluorescence spectra of the silica gel samples during light irradiation were also investigated. The relative band intensity due to the intermediate species between the original SNO and the merocyanine species decreased and that of the complex increased with the UV irradiation time. The reverse process was observed during visible irradiation. The UV irradiation effects on the chelation of SNO and its photochromic property also depended on the electron affinity of the metal ions.
    Photochemical and Photobiological Sciences 03/2012; 11(7):1164-73. · 2.92 Impact Factor
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    ABSTRACT: Unique Ni compound nanocrystals were successfully grown on carbon nanotubes (CNTs) by cooling a mixed chloride flux. Cup-stacked CNTs (CSCNTs) were used as the nanocarbon materials because of their structural features. The grown nanocrystals had a nanosheet structure, which was densely assembled and had a ribbon-like morphology. Therefore, the nanocrystal/CSCNT composites were expected to have a highly active surface area for the catalyst composites. The selected area electron diffraction pattern and the related radial intensity profiles indicated that the grown nanocrystals were Ni(OH)2. When the pristine CSCNTs were used as a starting material, the formation efficiency of the nanocrystal/CSCNT composites decreased because the pristine CSCNTs were not dispersed in the KCl-LiCl flux. Therefore, functionalization of the CSCNTs was carried out with VUV light irradiation. The dispersibility of the VUV light-treated CSCNTs increased in the KCl-LiCl flux in comparison with the pristine CSCNTs because oxygen-containing functional groups, such as -COOH and -CO, were introduced onto the surfaces of the CSCNTs.
    Journal of Nanoscience and Nanotechnology 02/2012; 12(2):1530-4. · 1.15 Impact Factor
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    ABSTRACT: Potassium triniobate (KNb3O8), which is an oxide semiconductor photocatalyst, has a layered structure consisting of negatively charged sheets of linked NbO6 octahedral units and K+ ions between the sheets. We report the flux growth of KNb3O8 crystals and their application for the photocatalytic decomposition of organic thin films. First, high quality, idiomorphic KNb3O8 crystals were successfully grown by cooling a KCl flux. Transparent-colorless KNb3O8 crystals had relatively uniform sizes and shapes. The size, morphology and phase of the grown crystals were dependent on the holding temperature and solute concentration. Next, highly crystalline NbOxnanosheets were successfully prepared via a two-step process, that is, proton exchange and subsequent exfoliation of the KNb3O8 crystals. Finally, the nanosheet layer spin-coated on a silica glass was used for photodegradation of hydrophobic organosilane thin films. The fabricated layer was colorless and transparent, and it absorbed ultraviolet (UV) light with a wavelength less than 350 nm. When organosilane thin films were placed in contact with the nanosheet layer and UV light was irradiated to the organosilane thin films through the transparent nanosheet layer, the wettability of organosilane layers was drastically converted from hydrophobic to ultrahydrophilic. The highly crystalline nanosheet layer was found to exhibit excellent photocatalytic properties.
    CrystEngComm 01/2012; 14(3):987-992. · 3.88 Impact Factor

Publication Stats

210 Citations
190.47 Total Impact Points

Institutions

  • 2006–2014
    • Shinshu University
      • • Department of Environmental Science and Technology
      • • Department of Materials Science and Engineering
      • • Faculty of Engineering
      Shonai, Nagano, Japan
  • 2011
    • National Institute of Advanced Industrial Science and Technology
      • Materials Research Institute for Sustainable Development
      Nagoya-shi, Aichi-ken, Japan
  • 2001–2005
    • Nagoya University
      • Graduate School of Engineering
      Nagoya, Aichi, Japan