Faculty Profiles - KOBAYASHI Makoto

Papers - KOBAYASHI Makoto

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Hierarchical structures of rutile exposing high-index facets Reviewed International journal

Quang Duc Truong, Hideki Kato, Makoto Kobayashi, Masato Kakihana

JOURNAL OF CRYSTAL GROWTH Vol. 418 page： 86 - 91 2015.5

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Recently, shape-controlled synthesis of crystals exposing high-index facets has attracted much research interest due to their importance for both fundamental studies and technological applications. Herein, crystals of rutile-type TiO2 with hierarchical structures exposing high-index facets have been synthesized by a facile hydrothermal method using water-soluble titanium complex as a precursor and picolinic acid as structure-directing and shape-controlling agents. The synthesized particles were composed of several branches of pyramidal crystals with relatively smooth surface. On the basis of investigation results, it was speculated that the mutual pi-stacking and selective adsorption of picolinic acid on specific {111} facets resulted in the formation of rutile crystals bound by high-index surfaces such as {331}. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2015.02.056

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Syntheses of silicate phosphors by aqueous solution techniques using water-dispersible inorganic Si cluster Reviewed International journal

Yasushi Sato, Hideki Kato, Makoto Kobayashi, Jihae Kim, Masato Kakihana

Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy Vol. 62 ( 4 ) page： 127 - 133 2015.4

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Journal of the Japan Society of Powder and Powder Metallurgy

In this paper, we demonstrated the synthesis of silicate-based phosphors by solution techniques using glycolmodified silane (GMS) as a Si source. GMS is a water-dispersible inorganic Si cluster, which is vitally involatile and nonflammable compounds, compared to volatile and flammable Si-alkoxides such as tetraethoxysilane (TEOS). Therefore, GMS has allowed the silicon containing compounds to be synthesized through various solution processes for ceramic compounds such as polymerizable complex (PC) and amorphous metal complex (AMC) methods. This paper provides examples of synthesis of new silicate-based phosphors such as NaAlSiO4:Eu2+, BaZrSi3O9:Eu2+, and CaSrSiO4:Eu2+. In addition, other examples of improvement of emission for conventional silicate-based phosphors, Y2SiO5:Ce3+-Tb3+ and Zn2SiO4:Mn2+, prepared by the above solution techniques including homogeneous precipitation using GMS are also given in this paper.

DOI： 10.2497/jjspm.62.127

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Design of crystal structures, morphologies and functionalities of titanium oxide using water-soluble complexes and molecular control agents Invited Reviewed International journal

Makoto Kobayashi, Minoru Osada, Hideki Kato, Masato Kakihana

Polymer Journal Vol. 47 ( 2 ) page： 78 - 83 2015.2

Language：English Publishing type：Research paper (scientific journal) Publisher：NATURE PUBLISHING GROUP

Nature produces materials with excellent physical and chemical properties using water as a medium under ambient temperature and pressure. The current need for more highly functional and compact materials makes the mimicking of natural processes to produce these materials a very interesting approach, not only to obtain highly functionalized materials but also to reduce the environmental impact. Our research group is engaged in the development of new stable water-soluble compounds that follow natural processes for the synthesis of materials using water as a medium. This paper summarizes a hydrothermal synthesis of rutile-type titanium oxide using water-soluble titanium complexes, controlling the crystal morphology by utilizing organic molecules as shape-control agents as well as their speculative formation mechanism and superior dielectric properties of unusually shaped titanium oxide crystals. By recapitulating our results, we indicate that control of the nano-and macro-structures and functional improvement are accomplished through the development of new precursor compounds.

DOI： 10.1038/pj.2014.89

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Crystal structures and luminescence properties of Eu²⁺-activated new NaBa_0.5Ca_0.5PO₄ and Na₃Ba₂Ca(PO₄)₃. Reviewed International journal

Minsung Kim, Makoto Kobayashi, Hideki Kato, Hisanori Yamane, Yasushi Sato, Masato Kakihana

Dalton transactions Vol. 44 ( 4 ) page： 1900 - 4 2015.1

Language：English Publishing type：Research paper (scientific journal)

NaBa(1-x)Ca(x)PO4:Eu(2+) were synthesized using polymerizable complex method. New phases were observed at x = 1/3 and 0.5, which were identified by single-crystal XRD analysis as Na3Ba2Ca(PO4)3 and NaBa0.5Ca0.5PO4 with a trigonal system. Though both phases pretend to be solid solutions between NaBaPO4 and NaCaPO4, they have different coordination environments and PO4 orderings. 1 mol% Eu(2+)-activated NaBaPO4, Na3Ba2Ca(PO4)3, and NaBa0.5Ca0.5PO4 exhibited an emission maximum at 435 nm, 458 nm, and 460 nm, respectively. The shift of the emission maximum might be due to a change in the Eu-O bond length.

DOI： 10.1039/c4dt03024a

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Controlled radical polymerization of styrene with magnetic iron oxides prepared through hydrothermal, bioinspired, and bacterial processes Reviewed International journal

Arihiro Kanazawa, Kotaro Satoh, Shokyoku Kanaoka, Masato Kakihana, Makoto Kobayashi, Junki Sato, Hiroaki Imai, Yuya Oaki, Atsushi Arakaki, Kiyofumi Katagiri, Masami Kamigaito, Sadahito Aoshima

RSC ADVANCES Vol. 5 ( 63 ) page： 51122 - 51129 2015

Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

Controlled/living radical polymerization was examined with the use of magnetic iron oxide (Fe3O4) prepared through various processes, including hydrothermal synthesis, a bioinspired process, and magnetotactic bacteria. Prior to the use of various types of Fe3O4, commercially available Fe3O4 was employed as a heterogeneous catalyst for styrene polymerization in conjunction with an alkyl halide as an initiator. Under appropriately optimized conditions, with the addition of Ph3P in a solvent mixture of toluene and DMF, the polymerization proceeded in a well-controlled manner. In addition, solid Fe3O4 was recovered using a magnetic approach and was reused for a polymerization reaction. The effects of stirring on the polymerization rate suggest that the surface of Fe3O4 is responsible for the catalysis in polymerization. Fe3O4 samples prepared through various processes were then used for styrene polymerization and showed different activities depending on the preparation process. In particular, Fe3O4 prepared through hydrothermal synthesis exhibited a much higher activity compared with commercial Fe3O4.

DOI： 10.1039/c5ra09149g

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Improvement of hydrogen evolution under visible light over Zn_1-2x(CuGa)_xGa₂S₄ photocatalysts by synthesis utilizing a polymerizable complex method Reviewed International journal

Ciro Scheremeta Quintans, Hideki Kato, Makoto Kobayashi, Hiroshi Kaga, Akihide Iwase, Akihiko Kudo, Masato Kakihana

Journal of Materials Chemistry A Vol. 3 ( 27 ) page： 14239 - 14244 2015

Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

Single phase Zn1-2x(CuGa)(x)Ga2S4 was successfully synthesized by a two-step route: synthesis of an oxide precursor by a polymerizable complex (PC) method followed by sulfurization under a H2S-Ar flow. The samples thus obtained were porous aggregates consisting of fine crystals with 50 nm size. Among the examined compositions, Zn-0.4(CuGa)(0.3)Ga2S4 (x = 0.3) showed the highest activity for H-2 evolution from an aqueous solution containing S2- and SO32- as electron donors under visible light irradiation. The apparent quantum yield of the optimized sample with deposition of 2 wt% of Rh was 19% at 420 nm. This value is higher than that of the sample synthesized by a solid state reaction (15%). Therefore, improvement of the photocatalytic performance of Zn-0.4(CuGa)(0.3)Ga2S4 for H-2 evolution has been achieved by using the two-step synthesis method including the preparation of an oxide precursor by the PC method.

DOI： 10.1039/c5ta02114f

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Photocatalytic water oxidation under visible light by valence band controlled oxynitride solid solutions LaTaON₂-SrTiO₃ Reviewed International journal

Hideki Kato, Koichiro Ueda, Makoto Kobayashi, Masato Kakihana Masato

Journal of Materials Chemistry A Vol. 3 ( 22 ) page： 11824-11829 - 11829 2015

A carbon modified NaTaO₃ mesocrystal nanoparticle with excellent efficiency of visible light induced photocatalysis Reviewed International journal

Xiaoyong Wu, Shu Yin, Bin Liu, Makoto Kobayashi, Masato Kakihana, Tsugio Sato

Journal of Materials Chemistry A Vol. 2 ( 48 ) page： 20832 - 20840 2014.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Royal Society of Chemistry

A carbon modified NaTaO&lt
inf&gt
3&lt
/inf&gt
mesocrystal nanoparticle (ca. 20 nm) was successfully synthesized by a one-pot solvothermal method, employing TaCl&lt
inf&gt
5&lt
/inf&gt
and NaOH as the starting materials and distilled water/EG mixed solution as a reaction solvent in the presence of appropriate amounts of glucose. The mesocrystal sample presented a high specific surface area 90.8 m&lt
sup&gt
2&lt
/sup&gt
g&lt
sup&gt
-1&lt
/sup&gt
with large amounts of well-dispersed mesopores in the particle, owing to the co-effect of EG and glucose during the reaction process. A non-classic mechanism of formation was proposed for the growth of the NaTaO&lt
inf&gt
3&lt
/inf&gt
mesocrystal. Furthermore, the NaTaO&lt
inf&gt
3&lt
/inf&gt
mesocrystal exhibited considerably improved visible light absorption in addition to the intrinsic UV light absorption as a result of carbon modification originated from glucose. On the basis of the large specific surface area, high crystallinity and optical property, the carbon modified NaTaO&lt
inf&gt
3&lt
/inf&gt
mesocrystal demonstrated excellent efficiency for continuous NO gas destruction under irradiation of UV, short wavelength visible lights (&gt
400 m) and even long wavelength visible light (&gt
510 nm), considerably superior to those of the unmodified NaTaO&lt
inf&gt
3&lt
/inf&gt
specimen and commercial titania, P25. The carbon modified NaTaO&lt
inf&gt
3&lt
/inf&gt
mesocrystal nanoparticles prepared in this work would probably have potential utilization in environmental purification and energy conversion.

DOI： 10.1039/c4ta04132a

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Development of two novel Eu²⁺-activated phosphors in the Na-Sc-Si-O system and their photoluminescence properties Reviewed International journal

Jihong Min, Taichi Yamaguchi, Hideki Kato, Makoto Kobayashi, Hisanori Yamane, Masato Kakihana

Journal of Luminescence Vol. 154 page： 285 - 289 2014.10

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Two novel Eu2+-activated phosphors in the Na-Sc-Si-O system were developed in this study, NaScSi2O6:Eu and Na3ScSi3O9:Eu. NaScSi2O6:Eu2+ showed yellow emission with a peak at 555 nm under excitation at 220-430 nm. When flux-treatment was performed for NaScSi2O6:Eu2+, we found the existence of a new phase. We then succeeded in synthesis of a high-purity sample of this new compound by a parallel solution synthesis method. It was revealed that the new phase was Na3ScSi3O9 with isostructure to Na3YSi3O9, and Eu2+-activated Na3ScSi3O9 exhibited photoluminescence. Na3ScSi3O9:Eu showed green emission with a peak at 530 nm and a corresponding broad excitation band up to 500 nm. However, photoluminescence of Eu2+ was negligible for Na3YSi3O9:Eu because of the stabilization of Eu3+ at the Y3+ site. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jlumin.2014.05.006

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Synthesis of (Ca1-xSrx)(4)Si2O7F2 oxyfluoride solid solutions and their photoluminescence properties activated by Eu2+ ions Reviewed International journal

Jihong Min, Hideki Kato, Makoto Kobayashi, Yasushi Sato, Masato Kakihana

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN Vol. 122 ( 1428 ) page： 630 - 633 2014.8

Language：English Publishing type：Research paper (scientific journal) Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI

The synthesis of oxyfluoride solid solutions with the composition (Ca1-xSrx)(4)Si2O7F2 is reported in this study. (Ca1-xSrx)(4)Si2O7F2 is found to form a solid solution within the entire composition range. Synthesis of Sr4Si2O7F2, which is the first compound in the Sr-Si-O-F system, can be regarded as one of the interesting results of this study. The Eu2+-activated (Ca1-xSrx)(4)Si2O7F2 solid solutions, except for Sr4Si2O7F2 exhibited photoluminescence under excitation at 300-450nm at room temperature. The samples with x = 0.25-0.75 showed a broad red emission band with a peak around 630 nm, whereas the Ca4Si2O7F2:Eu2+ (x = 0) showed blue emission with a peak at 470 nm. Thus, the substitution of Sr for Ca in Ca4SiO7F2:Eu2+ changed the photoluminescence properties remarkably. (C) 2014 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.122.630

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The significance of phosphate source in the preparation of functional luminescent phosphate materials Reviewed International journal

Minsung Kim, Makoto Kobayashi, Hideki Kato, Masato Kakihana

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN Vol. 122 ( 1428 ) page： 626 - 629 2014.8

Language：English Publishing type：Research paper (scientific journal) Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI

The stability and reactivity of phosphate raw materials, including two water-soluble phosphates, ethylene glycol-conjugated phosphate (EG-P), and polyethylene glycol-conjugated phosphate (PEG-P) developed by our group, were examined with the aim of synthesizing phosphates with high functionalities. EG-P was found to gradually hydrolyze in an aqueous solution, resulting in the formation of H3PO4, while PEG-P was stable for more than two months. EG-P and PEG-P did not form insoluble materials in aqueous solution in the presence of many other cations, while precipitates were often observed using conventional phosphate raw materials. In particular, there were no precipitates in an aqueous solution of PEG-P in the presence of Ca2+ and Li+ ions, which easily formed insoluble phosphates in a given aqueous condition. Consequently, single-phase LiCaPO4 with high luminescence properties could be obtained by a polymerizable complex method employing PEG-P, while impurity phases were formed using other P sources, and KSrPO4 was formed as a single phase using EG-P and PEG-P. (C) 2014 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.122.626

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Tailoring of deep-red luminescence in Ca₂SiO₄:Eu²⁺ Reviewed International journal

Yasushi Sato, Hideki Kato, Makoto Kobayashi, Takaki Masaki, Dae-Ho Yoon, Masato Kakihana

Angewandte Chemie (International ed. in English) Vol. 53 ( 30 ) page： 7756 - 9 2014.7

Language：English Publishing type：Research paper (scientific journal)

We report a new dicalcium silicate phosphor, Ca(2-x)Eu(x)SiO4, which emits red light in response to blue-light excitation. When excited at 450 nm, deep-red emission at 650 nm was clearly observed in Ca1.2Eu0.8SiO4, the external and internal quantum efficiencies of which were 44 % and 50 %, respectively. The red emission from Ca(2-x)Eu(x)SiO4 was strongly related to the peculiar coordination environments of Eu(2+) in two types of Ca sites. The red-emitting Ca2SiO4:Eu(2+) phosphors are promising materials for next-generation, white-light-emitting diode applications.

DOI： 10.1002/anie.201402520

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Photoluminescence properties of deep-red emitting Ca₂SiO₄:Eu²⁺ International journal

Y. Sato, H. Kato, M. Kobayashi, M. Kakihana

Rare Earths Vol. 64 page： 122 - 123 2014.5

Insights into a selective synthesis of anatase, rutile, and brookite-type titanium dioxides by a hydrothermal treatment of titanium complexes Reviewed International journal

Mitsuru Yoshizawa, Makoto Kobayashi, Valery Petrykin, Hideki Kato, Masato Kakihana

JOURNAL OF MATERIALS RESEARCH Vol. 29 ( 1 ) page： 90 - 97 2014.1

Language：English Publishing type：Research paper (scientific journal) Publisher：CAMBRIDGE UNIV PRESS

Novel water-soluble titanium complexes coordinated by hydroxycarboxylic acids or amines were developed, and the hydrothermal treatment of the new complexes was carried out to elucidate the formation mechanism of the titania polymorphs including rutile, anatase, and brookite. An empirical relationship among the crystal structure of TiO2, the ligand, and the complex structure was found. Anatase, rutile, or a mixture of both was obtained by the hydrothermal treatment of the complexes coordinated by hydroxycarboxylic acids. The structure of complexes prepared using hydroxycarboxylic acids, which have one hydroxyl and one carboxylic groups, seems to be preferable for the formation of rutile. It was also found that the hydrothermal treatment of titanium complexes coordinated by amine with NAc2 structure resulted in the formation of brookite. Thus, the effect of ligand and complex structure on the crystal structure of TiO2 synthesized by the hydrothermal treatment of the complexes was proposed.

DOI： 10.1557/jmr.2013.229

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Hydrothermal synthesis of magnetite particles with uncommon crystal facets Reviewed International journal

Junki Sato, Makoto Kobayashi, Hideki Kato, Takamichi Miyazaki, Masato Kakihana

Journal of Asian Ceramic Societies Vol. 2 ( 3 ) page： 258 - 262 2014

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier B.V.

Hydrothermal synthesis of Fe3O4 (magnetite) particles was carried out using organic compounds as morphology control agents to obtain magnetite crystals with uncommon facets. It was established that the morphology of Fe3O4 crystals obtained by hydrothermal treatment of an aqueous solution containing Fe2+ and organic compounds depended on the organic compound used. The shape of the Fe3O4 particles obtained when no additives were used was quasi-octahedral. In contrast, the addition of picolinic acid, citric acid or pyridine resulted in the formation of polyhedral crystals, indicating the presence of not only {111}, {100} and {110} facets but also high-index facets including at least {311} and {331}. When citric acid was used as an additive, octahedral crystals with {111} facets also appeared, and their size decreased as the amount of citric acid was increased. Thus, control of Fe3O4 particle morphology was achieved by a simple hydrothermal treatment using additives. © 2014 The Ceramic Society of Japan and the Korean Ceramic Society.

DOI： 10.1016/j.jascer.2014.05.008

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Synthesis of Titanium Dioxide Nanocrystals with Controlled Crystal- and Micro-structures from Titanium Complexes Invited Reviewed

Makoto Kobayashi, Hideki Kato, Masato Kakihana

Nanomaterials and Nanotechnology Vol. 3 ( 23 ) page： 1-10 2013.12

水溶性チタン錯体を用いたbrookite型酸化チタン粒子の調製 Invited Reviewed

小林亮

Colloid and Interface Communication Vol. 38 ( 4 ) page： 7-8 2013.12

水を反応場として用いた機能性無機材料の合成～環境調和型プロセスの設計と新規水溶性金属錯体の開発～ Invited Reviewed

小林亮, 垣花眞人

分離技術 Vol. 41 ( 6 ) page： 32(368)-36(372) 2013.12

A Highly Luminous LiCaPOCa₄:Eu#U2+ Phosphor Synthesized by a Solution Method Employing a Water-Soluble Phosphate Ester Reviewed International journal

Minsung Kim, Makoto Kobayashi, Hideki Kato, Masato Kakihana

Optics and Photonics Journal Vol. 3 ( 6A ) page： 13-18 2013.10

Exploration of New Phosphors Using a Mineral-Inspired Approach in Combination with Solution Parallel Synthesis Invited Reviewed International journal

Masato Kakihana, Jihae Kim, Tetsufumi Komukai, Hideki Kato, Yasushi Sato, Makoto Kobayashi, Yuji Takatsuka

Optics and Photonics Journal Vol. 3 ( 6A ) page： 5-12 2013.10

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Papers - KOBAYASHI Makoto