Papers - KOBAYASHI Makoto

Z-scheme water splitting utilizing CuLi_1/3Ti_2/3O₂ as a hydrogen-evolving photocatalyst with response up to 600 nm Invited Reviewed

Shunya Yoshino, Tanya Kurutach, Qingshan Liu, Toshiki Yamanaka, Shunsuke Nozawa, Makoto Kobayashi, Hiromu Kumagai, Hideki Kato

Sustainable Energy & Fuels   Vol. 8 ( 6 ) page： 1260 - 1268   2024.2

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DOI： 10.1039/D3SE01622F

Multiemission of Ce³⁺ from Single Crystallographic Site Induced by Disordering of Ions Reviewed

Takuya Yasunaga, Makoto Kobayashi, Kenji Oqmhula, Huan Qi, Tom Ichibha, Kenta Hongo, Shunsuke Yamamoto, Ryo Maezono, Masaya Mitsuishi, Minoru Osada, Hideki Kato, Masato Kakihana

Inorganic Chemistry   Vol. 63 ( 2 ) page： 1288 - 1295   2024.1

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DOI： 10.1021/acs.inorgchem.3c03789

Hetero-assembly design of 2D oxide nanosheets for tailored thermal shielding materials Reviewed

Hirofumi Tsunematsu, Keita Nishibashi, Eisuke Yamamoto, Makoto Kobayashi, Tomohiro Yoshida, Minoru Osada

Applied Physics Express   Vol. 17   page： 015002   2024.1

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DOI： 10.35848/1882-0786/ad13ce

Facile Synthesis of Pd Nanosheets and Implications for Superior Catalytic Activity Reviewed

Sumiya Ando, Eisuke Yamamoto, Makoto Kobayashi, Akichika Kumatani, Minoru Osada

ACS Nano   Vol. 18 ( 1 ) page： 461 - 469   2023.11

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DOI： 10.1021/acsnano.3c07861

Gigantic Thermal Shielding in 2D Oxide Nanosheets Reviewed

Hirofumi Tsunematsu, Yue Shi, Eisuke Yamamoto, Makoto Kobayashi, Tomohiro Yoshida, Minoru Osada

ACS Nano   Vol. 17 ( 2 ) page： 11396 - 11405   2023.5

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DOI： 10.1021/acsnano.3c00815

Ultrahigh Energy Storage in 2D High-κ Perovskites Reviewed

Hyung-Jun Kim, Shu Morita, Ki-Nam Byun, Yue Shi, Takaaki Taniguchi, Eisuke Yamamoto, Makoto Kobayashi, Yasuo Ebina, Takayoshi Sasaki, Minoru Osada

Nano Letters   Vol. 23 ( 9 ) page： 3788 - 3795   2023.5

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

DOI： 10.1021/acs.nanolett.3c00079

2D Bismuth Oxyfluorides: A New Member of Cationic Nanosheets Reviewed

Makoto Kobayashi, Tsubasa Tasaka, Eisuke Yamamoto, Minoru Osada

Chemistry Letters   Vol. 52 ( 6 ) page： 449 - 451   2023.4

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DOI： 10.1246/cl.230136

Pseudo-Topotactic Transformation from Oxide Nanosheets to Amorphous Nanosheets Reviewed

Hikaru Sugimoto, Makoto Kobayashi, Eisuke Yamamoto, Minoru Osada

Chemistry Letters   Vol. 52 ( 5 ) page： 322 - 324   2023.4

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DOI： 10.1246/cl.230073

Composite design of 2D inorganic nanosheets for flexible energy storage capacitors Reviewed

Ki Nam Byun, Shi Yue, Eisuke Yamamoto, Makoto Kobayashi, Minoru Osada

Journal of the Ceramic Society of Japan   Vol. 131 ( 4 ) page： 77 - 82   2023.4

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DOI： 10.2109/jcersj2.22150

Automated One-Drop Assembly for Facile 2D Film Deposition Reviewed

Yue Shi, Eisuke Yamamoto, Makoto Kobayashi, Minoru Osada

ACS Applied Materials & Interfaces   Vol. 15 ( 18 ) page： 22737 - 22743   2023.3

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DOI： 10.1021/acsami.3c02250

Free-standing Molecularly Thin Amorphous Silica Nanosheets Reviewed

Eisuke Yamamoto, Kosuke Fujihara, Yuma Takezaki, Kentaro Ito, Yue Shi, Makoto Kobayashi, Minoru Osada

Small   Vol. 19 ( 22 ) page： 2300022   2023.2

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DOI： 10.1002/smll.202300022

Molecularly Thin BaTiO₃ Nanosheets with Stable Ferroelectric Response Reviewed International coauthorship

Kazuki Hagiwara, Ki Nam Byun, Shu Morita, Eisuke Yamamoto, Makoto Kobayashi, Xioyang Liu, Minoru Osada

Advanced Electronic Materials   Vol. 9 ( 3 ) page： 2291239   2023.2

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DOI： 10.1002/aelm.202201239

Damage-free LED lithography for atomically thin 2D material devices Reviewed

Yue Shi, Takaaki Taniguchi, Ki-Nam Byun, Daiki Kurimoto, Eisuke Yamamoto, Makoto Kobayashi, Kazuhito Tsukagoshi, Minoru Osada

Scientific Reports   Vol. 13 ( 1 ) page： 2583   2023.2

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DOI： 10.1038/s41598-023-29281-w

Improved energy storage performance of PVDF nanocapacitors by utilizing 2D inorganic barrier Reviewed International coauthorship

Byun Ki-Nam, Eisuke Yamamoto, Makoto Kobayashi, Minoru Osada

Chemistry Letters   Vol. 52 ( 1 ) page： 51 - 54   2022.11

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DOI： 10.1246/cl.220466

Tailored synthesis of molecularly thin platinum nanosheets using designed 2D surfactant solids Invited Reviewed

Eisuke Yamamoto, Akiko Suzuki, Makoto Kobayashi, Minoru Osada

Nanoscale   Vol. 14 ( 32 ) page： 11561 - 11567   2022.6

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DOI： 10.1039/D2NR01807A

Influences of pulverization and annealing treatment on photocatalytic activity of BiVO₄ for oxygen evolution Reviewed

Kazuya Okuno, Hiromu Kumagai, Junie Jhon M. Vequizo, Kosaku Kato, Makoto Kobayashi, Akira Yamakata, Masato Kakihana, Hideki Kato

Sustainable Energy Fuels   Vol. 6 ( 7 ) page： 1698 - 1707   2022.2

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

DOI： 10.1039/D2SE00065B

Synthesis of brookite-type TiO₂ nanoparticles by emulsion assisted hydrothermal method using titanium glycolate complex Reviewed

Kohei Kasuya, Md. Shahiduzzaman, Makoto Kobayashi, Shu Yin, Masato Kakihana, Koji Tomita

Journal of the Ceramic Society of Japan   Vol. 129 ( 12 ) page： 720 - 724   2021.12

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DOI： 10.2109/jcersj2.21127

Facile titania nanocoating using single droplet assembly of 2D nanosheets Reviewed International journal

Yue Shi, Eisuke Yamamoto, Makoto Kobayashi, Minoru Osada

Journal of the Ceramic Society of Japan     2021.4

Synthesis of NaMoO₃F and Na₅W₃O₉F₅ with Morphological Controllability in Non-Aqueous Solvents Reviewed International journal

Yusuke Asakura, Tomoyo Akahira, Makoto Kobayashi, Minoru Osada, Shu Yin

Inorganic Chemistry   Vol. 59 ( 15 ) page： 10707 - 10716   2020.8

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DOI： 10.1021/acs.inorgchem.0c01175

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Z-scheme water splitting by microspherical Rh-doped SrTiO₃ photocatalysts prepared by a spray drying method Reviewed International journal

Hong Phong Duong, Takahiro Mashiyama, Makoto Kobayashi, Akihide Iwase, Akihiko Kudo, Yusuke Asakura, Shu Yin, Masato Kakihana, Hideki Kato

Applied Catalysis B: Environmental   Vol. 252   page： 222 - 229   2019.9

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.apcatb.2019.04.009

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Anisotropy in Stable Conformations of Hydroxylate Ions between the {001} and {110} Planes of TiO₂ Rutile Crystals for Glycolate, Lactate, and 2-Hydroxybutyrate Ions Studied by Metadynamics Method. Reviewed International journal

Hiroki Nada, Makoto Kobayashi, Masato Kakihana

ACS omega   Vol. 4 ( 6 ) page： 11014 - 11024   2019.6

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Control over TiO2 rutile crystal growth and morphology using additives is essential for the development of functional materials. Computer simulation studies on the thermodynamically stable conformations of additives at the surfaces of rutile crystals contribute to understanding the mechanisms underlying this control. In this study, a metadynamics method was combined with molecular dynamics simulations to investigate the thermodynamically stable conformations of glycolate, lactate, and 2-hydroxybutyrate ions at the {001} and {110} planes of rutile crystals. Two simple atom-atom distances were selected as collective variables for the metadynamics method. At the {001} plane, a conformation in which the COO- group was oriented toward the surface was found to be the most stable for the lactate and 2-hydroxybutyrate ions, whereas a conformation in which the COO- group was oriented toward water was the most stable for the glycolate ion. At the {110} plane, a conformation in which the COO- group was oriented toward the surface was the most stable for all three hydroxylate ions, and a second most stable conformation was also observed for the lactate ion at positions close to the {110} plane. For all three hydroxylate ions (α-hydroxycarboxylate ions), the stability of the most stable conformation was higher for the {110} plane than for the {001} plane. At both planes, the stability of the most stable conformation was highest for the 2-hydroxybutyrate ion and lowest for the glycolate ion. Supposing that all three hydroxylate ions serve to decrease the surface free energy at the rutile surface and that a more stable conformation at the rutile surface leads to a greater decrease in the surface free energy, the present results partially explain experimentally observed differences in the changes in growth rate and morphology of rutile crystals in the presence of glycolic, lactic, and 2-hydroxybutyric acids.

DOI： 10.1021/acsomega.9b01100

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Selective Synthesis and Photocatalytic Oxygen Evolution Activities of Tantalum/Nitrogen-Codoped Anatase, Brookite and Rutile Titanium Dioxide Reviewed International journal

Nishioka, Shunta, Kobayashi, Makoto, Lu, Daling, Kakihana, Masato, Maeda, Kazuhiko

Bulletin of the Chemical Society of Japan   Vol. 92 ( 6 ) page： 1032 - 1038   2019.6

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Tantalum/nitrogen codoped titanium dioxide (TiO2:Ta,N) having a rutile structure has recently been reported to be a good photocatalyst for visible-light water oxidation. In this work, three different polymorphs of TiO2:Ta,N (anatase, brookite and rutile) were synthesized by a hydrothermal method using water-soluble titanium/tantalum complexes as precursors, followed by thermal nitridation with dry ammonia gas. Effects of the physicochemical properties on photocatalytic activity for O-2 evolution from an aqueous silver nitrate solution under visible light (lambda > 400 nm) were investigated. Experimental results indicated that defect formation during the nitridation procedure was the dominant factor for photocatalytic activity. Anatase TiO2:Ta,N was the most active for O-2 evolution among the three polymorphs, and also served as an O-2 evolution photocatalyst in Z-scheme overall water splitting in combination with Rh-doped strontium titanate (SrTiO3:Rh) and an Fe3+/Fe2+ redox-shuttle mediator.

DOI： 10.1246/bcsj.20190037

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Synthesis of Ba_1-xSr_#x#IRYSi₂O₅N and Discussion Based on Structure Analysis and DFT Calculation Reviewed International journal

Takuya Yasunaga, Makoto Kobayashi, Kenta Hongo, Kotaro Fujii, Shunsuke Yamamoto, Ryo Maezono, Masatomo Yashima, Masaya Mitsuishi, Hideki Kato, Masato Kakihana

Journal of Solid State Chemistry   Vol. 276   page： 266-271   2019.5

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DOI： 10.1016/j.jssc.2019.05.012

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Crystal structures of Ca_4+xY_3-xSi₇O_15+xN_5-x (0 <= x <= 1) comprising of an isolated [Si₇(O,N)₁₉] unit Reviewed International journal

Kobayashi, Makoto, Yasunaga, Takuya, Kato, Hideki, Fujii, Kotaro, Yashima, Masatomo, Kakihana, Masato

Acta Crystallographica Section E: Crystallographic Communications   Vol. 75   page： 260 - +   2019.2

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：INT UNION CRYSTALLOGRAPHY  

Single crystals of the solid solution series Ca(4+x)Y(3-x)Si(7)O(15+x)N(5-x )were obtained by a solid-state reaction method using a flux for x = 0, 0.5 and 1, resulting in Ca4Y3Si7O15N5 (tetracalcium triyttrium heptasilicon oxynitride), Ca-4.5 Y-2.5 Si7O15.5N4.5 and Ca5Y2Si7O16N4 (pentacalcium diyttrium heptasilicon oxynitride). Single-crystal X-ray analysis revealed that the three compounds are isotypic and belong to space-group type P6(3)/m. Ca2+ and Y3+ cations are distributed over two crystallographic sites (site symmetry (3) over bar.. and 1) in a disordered manner. The corresponding (Ca,Y)-centred polyhedra are connected by edge-sharing, resulting in the formation of a layer structure extending parallel to (001). Three [Si(O,N)](4) tetrahedra (two with point group symmetry m one with 3.. and half-occupancy) are condensed into an isolated [Si-7(O,N)(19)] unit, in which an [Si(O,N)](4) tetrahedron is located at the center of a 12-membered oxynitride ring with composition [Si6O15N3]. The present compounds are the first to have such an [Si-7(O,N)(1)(9)] unit in their structures.

DOI： 10.1107/S2056989019001257

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Hydrothermal Synthesis of Pseudocubic Rutile-Type Titania Particles International journal

Makoto Kobayashi, Hideki Kato, Takamichi Miyazaki, Masato Kakihana

Ceramics   Vol. 2 ( 1 ) page： 56-63   2019.1

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DOI： 10.3390/ceramics2010005

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Sodium titanium oxide bronze nanoparticles synthesized via concurrent reduction and Na⁺-doping into TiO₂(B) Reviewed International journal

Hasegawa, George, Tanaka, Moeko, Vequizo, Junie Jhon M., Yamakata, Akira, Hojo, Hajime, Kobayashi, Makoto, Kakihana, Masato, Inada, Miki, Akamatsu, Hirofumi, Hayashi, Katsuro

Nanoscale   Vol. 11 ( 3 ) page： 1442 - 1450   2019.1

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

A mixed valence compound, sodium titanium oxide bronze (NaxTiO2-B), combines intriguing properties of high electric conductivity and good chemical stability together with a unique one-dimensional tunnel crystal structure available for cation storage. However, this compound has not been studied for a long period because of the strongly reductive condition at high temperature required for its preparation, which limits the morphological control such as the preparation of nanocrystals. For the first time in this paper, the topotactic synthesis of nano-sized NaxTiO2-B with high specific surface area (>130 m(2) g(-1)) from TiO2(B) nanoparticles has been demonstrated. The reaction of metastable TiO2(B) with NaBH4 allows carrier electrons to be doped simultaneously with incorporation of Na+ ions into the interstitial sites of the host Ti-O lattice at relatively low temperature. An electrochemical investigation of Li+- and Na+-ion storage behaviors suggests that the incorporated Na+ ions are mainly placed in the 6-fold coordination sites of bronze. In addition, optical measurements including time-resolved transient spectroscopy revealed that the doped electrons in the NaxTiO2-B nanoparticles are predominantly in the Ti3+ state and behave as a small polaron. The pelletized NaxTiO2-B nanoparticles shows a good electronic conductivity of 1.4 x 10(-2) S cm(-1) at 30 degrees C with an activation energy of 0.17 eV, which is attributable to the thermal barrier for the polaron hopping.

DOI： 10.1039/c8nr08372j

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B-site-ordered Double-perovskite Oxide Up-conversion Phosphors Doped with Yb and Ho, Er, or Tm Reviewed International journal

Kasuya, Kohei, Sato, Yasushi, Kobayashi, Makoto, Kato, Hideki, Kakihana, Masato, Tomita, Koji

Journal of Photopolymer Science and Technology   Vol. 32 ( 4 ) page： 593 - 596   2019

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TECHNICAL ASSOC PHOTOPOLYMERS,JAPAN  

B-site-ordered double-perovskite oxide up-conversion phosphors La2ZnTiO6, La2MgTiO6, and Ba2LaTaO6 doped with Yb and Ho, Er, or Tm were synthesized by a citric acid complex gelation method and a polymerizable complex method. Under 980-nm excitation, the double-perovskite oxide phosphors doped with luminescent ions at the A-site (La2ZnTiO6 and La2MgTiO6) showed stronger up-conversion emission than the phosphor doped with luminescent ions at the B-site (Ba2LaTaO6). La2ZnTiO6 and La2MgTiO6, in which dopants occupied the A-site, showed different up-conversion emission behaviors because of structural distortion resulting from the substitution of B-site cations.

DOI： 10.2494/photopolymer.32.593

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Ce⁴⁺-based Compounds Capable of Photoluminescence by Charge Transfer Excitation under Near Ultraviolet-Visible Light Reviewed International journal

Dawei Wen, Hideki Kato, Makoto Kobayashi, Shunsuke Yamamoto, Masaya Mitsuishi, Kotaro Fujii, Masatomo Yashima, Masato Kakihana

Inorganic chemistry   Vol. 57 ( 23 ) page： 14524 - 14531   2018.12

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Ce4+-based charge transfer phosphor is not common and has been reported mainly in Sr2CeO4 with an excitation band peaking at ∼290 nm, mismatching with the near-ultraviolet light emitting diodes. Herein, we report a new series of Ce4+-based compounds Sr4.4Ce2.6REZnO12 (RE = Y, La, and Eu) capable of photoluminescence induced by O2--Ce4+ charge transfer excitation under near-ultraviolet-visible light. The crystal structure of Sr4.4Ce2.6EuZnO12 was determined by single crystal X-ray diffraction. The RE = La and Y samples were confirmed to be iso-structure compounds of the RE = Eu sample by powder X-ray diffraction. By introducing highly covalent Zn2+-O2- bonds into the framework, the Ce4+-O2- bonds are lengthened due to the effect of the Ce4+-O2--Zn2+ stretch. The lengthened Ce4+-O2- bond weakens the repulsion of the electrons between Ce4+ and O2-, thereby lowering the charge transfer energy to the visible light region. Incorporation of Eu3+ into the present compounds realized red emission under near-ultraviolet-visible excitation by the O2--Ce4+ charge transfer followed by energy transfer to Eu3+.

DOI： 10.1021/acs.inorgchem.8b01900

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Expansion of Photoresponse Window of BiVO₄ Photocatalyst by Doping of Chromium(VI) Reviewed International journal

Kazuya Okuno, Hideki Kato, Junie Jhon, M. Vequizo, Yamakata Akira, Hisayoshi Kobayashi, Makoto Kobayashi, Masato Kakihana

RSC Advances   Vol. 8 ( 67 ) page： 38140-38145   2018.11

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DOI： 10.1039/C8RA07830K

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Photoluminescence Properties of Layered Perovskite-type Strontium Scandium Oxyfluoride Activated with Mn⁴⁺ Reviewed

Hideki Kato*, Yohei Takeda, Makoto Kobayashi, Hisayoshi Kobayashi, Masato Kakihana

Frontiers in Chemistry   Vol. 6   page： 467   2018.10

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DOI： 10.3389/fchem.2018.00467

Structural Change in SrSiO₃ Induced by Introduction of Nitrogen Reviewed

Makoto Kobayashi, Jihae Kim, Hironori Sato, Takuya Yasunaga, Hideki Kato*, Kotaro Fujii, Masahiro Shiraiwa, Masatomo Yashima, Masato Kakihana

Chemistry Letters   Vol. 47 ( 10 ) page： 1327-1329   2018.10

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DOI： 10.1246/cl.180620

Effects of Crystal Structure on Up-Conversion Luminescence in Er³⁺/Yb³⁺ Co-Doped SrTa₄O₁₁ Reviewed International journal

Sayaka Tamura, Michio Iwaoka, Yasushi Sato, Makoto Kobayasi, Masato Kakihana, Koji Tomita

Chemistry Letters   Vol. 47 ( 10 ) page： 1282-1284   2018.10

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DOI： 10.1246/cl.180605

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High Temperature Hydrogen Gas Sensing Property of GaN Prepared from α-GaOOH Reviewed

Angga Hermawan, Yusuke Asakura, Makoto Kobayashi, Masato Kakihana, and Shu Yin*

Sensors and Actuators B: Chemical   Vol. 276   page： 388-396   2018.8

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DOI： 10.1016/j.snb.2018.08.021

Development of Mixed Anion Phosphors Invited Reviewed

Kobayashi Makoto, Kato Hideki, Kakihana Masato

Ceramics Japan   Vol. 52 ( 12 ) page： 816-819   2017.12

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Authorship：Lead author   Language：Japanese  

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Synthesis of Rare Earth Niobate and Tantalate Powders via a Peroxo Complex Route Reviewed International journal

Hideki Kato, Katsuya Shimizu, Kiyotaka Nakajima, Makoto Kobayashi, Masato Kakihana

Chemistry Letters   Vol. 46 ( 10 ) page： 1515 - 1517   2017.10

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Powders of REMO4 (RE: rare earth, M: Nb and Ta) were synthesized by a coprecipitation method employing water-soluble peroxo Nb/Ta complexes. This peroxo-based method is an aqueous solution route free from organics and halides. REMO4 was directly crystallized by annealing the precursor under moderate conditions. It has been revealed that the precursors are also useful for synthesis of oxynitrides under mild nitriding conditions.

DOI： 10.1246/cl.170652

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Effect of hydroxy and carboxy groups on anisotropic growth of rutile-type titania under hydrothermal conditions Reviewed International journal

Makoto Kobayashi, Sungho Lee, Hideki Kato, Masato Kakihana

Journal of Asian Ceramic Societies   Vol. 5 ( 3 ) page： 320 - 325   2017.9

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

Control of crystal growth leads to highly functional materials with desired morphologies. In this study, the relationship between select additives and the crystal growth of rutile-type titania under hydrothermal conditions using α-hydroxy acids, carboxylic acids, or alcohols as additives was systematically investigated. Without additives, rod-like rutile crystals with average dimensions of 295 nm × 67 nm were formed. Acceleration of the crystal growth was observed and the aspect ratios of the resulting rod-like crystals were found to increase in the presence of the additives. Alcohols promoted crystal growth along the c-axis, but not in the direction to perpendicular to [001]. Carboxylic acids accelerated the overall crystal growth and this increase was more enhanced along the c-axis than that along others. Both effects were observed using α-hydroxy acids. In addition, the present results implied that the size of the hydrocarbon groups in alcohols and α-hydroxy acids appeared to be related to the acceleration of crystal growth along the c-axis. Hydroxy groups may reduce the surface energy of the crystal facets perpendicular to the c-axis by their adsorption on those facets, resulting in the formation of rod-like crystals with high aspect ratio.

DOI： 10.1016/j.jascer.2017.06.006

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Growth of TiO₂ microspheres with a radially oriented configuration Reviewed International journal

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

CrystEngComm   Vol. 19 ( 32 ) page： 4832 - 4837   2017.8

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Crystalline mesoporous materials with oriented configurations are promising for high-performance energy storage and conversion devices. In this work, hierarchical microspheres constructed from radially oriented single-crystalline TiO2 nanorods have been fabricated by a facile hydrothermal approach using oxalic acid as a chelating and structure-directing agent. The obtained mesoporous TiO2 microspheres have been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Brunauer-Emmett-Teller specific surface area measurement to reveal their unique properties. The growth and assembly process of the nanorod-based microspheres were elucidated in view of chelation-assisted assembly. It was found that oxalic acid played a crucial role in the oriented assembly of nanorods into well-defined microspheres.

DOI： 10.1039/c7ce01158j

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Photoluminescence Properties of Double Perovskite Tantalates Activated with Mn4+, AE₂LaTaO₆:Mn⁴⁺ (AE = Ca, Sr, and Ba) Reviewed International journal

Yohei Takeda, Hideki Kato, Makoto Kobayashi, Shunsuke Nozawa, Hisayoshi Kobayashi, Masato Kakihana

Journal of Physical Chemistry C   Vol. 121 ( 34 ) page： 18837 - 18844   2017.8

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Tetravalent manganese is known as one of the candidate luminous centers to obtain red emission. There are still unclear factors in Mn4+-activated oxide phosphors to achieve intense emission. In this paper, we studied the photoluminescence properties of double perovskite-type tantalates AE(2)LaTaO(6) (AE = Ca, Sr, and Ba) activated with Mn4+. All AE(2)LaTaO(6):Mn exhibited Mn4+-emission in the deep red region under excitation by near ultraviolet-green light (300-570 nm) at room temperature. Co-substitution of Mg2+, Al3+, and Ti4+ compensates unbalanced charge caused by oxygen defects, resulting in the enhancement of Mn4(+-)emission. The present cosubstitution effect is different from the usual cosubstitution, such as the replacement of two Al3+ by Mn4+ and Mg2+, taking into consideration the charge balance between cations. Theoretical calculation of band structures based on density functional theory suggests the presence of two kinds of quenching schemes in AE(2)LaTaO(6):Mn, photoionization and electron transfer from valence band to t(2g) orbitals of Mn.

DOI： 10.1021/acs.jpcc.7b06280

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Development of Crystal Growth Based on Aqueous Solution Processes Invited Reviewed

Makoto Kobayashi

Ceramics Japan   Vol. 52 ( 7 ) page： 502-503   2017.7

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Synthesis and photocatalytic properties of tetragonal tungsten bronze type oxynitrides Reviewed International journal

Katsuya Shimizu, Hideki Kato, Makoto Kobayashi, Masato Kakihana

Applied Catalysis B: Environmental   Vol. 206   page： 444 - 448   2017.6

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

Synthesis of a series of oxynitride Ba3-chi La chi Ta5O14-chi N1+x (x= 0-1.5) with a tetragonal tungsten bronze (TTB) structure was examined using moist-NH3 and 5% NH3-N-2 as nitriding atmosphere. The samples with x=0-1 were successfully obtained as phase pure TTB oxynitride whereas the x= 1.5 samples gave a mixture of TTB oxynitride, Ta3N5, and LaTaO4. Absorption of TTB oxynitrides in visible region was enhanced as increasing the content of nitrogen. TTB oxynitrides exhibited both of H-2 and O-2 evolution under visible light in the presence of methanol and silver ions, respectively, as sacrificial reagents. Nitrogen poor surface in the samples synthesized under moist-NH3 atmosphere was modified by annealing treatment using 5% NH3, resulting in improvement of photocatalytic activity for H2 evolution. Evaluation using monochromatic light revealed that the apparent quantum efficiency of Ba2LaTa5O13N2 was higher than that of Ba3Ta5O14N. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apcatb.2017.01.057

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Synthesis, Structure, and Photoluminescence of a Novel Oxynitride BaYSi₂O₅N Activated by Eu²⁺ and Ce³⁺ Reviewed International journal

Makoto Kobayashi, Takuya Yasunaga, Hironori Sato, Hideki Kato, Kotaro Fujii, Masatomo Yashima, Masato Kakihana

Chemistry Letters   Vol. 46 ( 6 ) page： 795 - 797   2017.6

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A novel oxynitride, BaYSi2O5N, has been synthesized by a solid-state reaction method. Its crystal structure was determined by single-crystal X-ray analysis. Eu2+- and Ce3+-doped BaYSi2O5N exhibit broad blue emission with peaks around 459 and 412 nm under excitation at 250-450 and 250-370 nm, respectively. This is the first report on the synthesis of oxynitrides in the BaO-Y2O3-SiO2-Si3N4 system.

DOI： 10.1246/cl.170144

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Site occupancy and luminescence properties of Ca₃Ln(AlO)₃(BO₃)₄:Ce³⁺,Tb³⁺,Mn²⁺ (Ln = Y, Gd) Reviewed International journal

Dawei Wen, Hideki Kato, Makoto Kobayashi, Shunsuke Yamamoto, Masaya Mitsuishi, Masato Kakihana

Journal of Materials Chemistry C   Vol. 5 ( 18 ) page： 4578 - 4583   2017.5

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

In this work, novel single-phase white emitting Ca(3)Ln(AlO)(3)(BO3)(4): Ce3+, Tb3+, Mn2+ (Ln = Y and Gd) phosphors were synthesized by a conventional solid-state reaction method. The crystal structure and photoluminescence properties were investigated for the first time. The structure of Ca(3)Ln(AlO) (3)(BO3)(4) was formed by AlO6 octahedral chains interconnected by BO3 triangles. Along the [001] direction, the Ca/Ln cations fill in the trigonal and hexagonal tunnels. For Ca(3)Ln(AlO)(3)(BO3)(4): Ce3+ and Ca(3)Ln(AlO)(3)(BO3)(4): Mn2+, large Ce3+ preferred to occupy the smaller coordination site, while small Mn2+ occupied the larger coordination site, which was explained by the space hindrance. Due to the cation disorder, the local environment of Ce3+ was complicated and the emission band was extremely broad. In Ca(3)Ln(AlO) (3)(BO3)(4), the emission color can be tuned from blue to green or red by tuning the Ce3+-Tb3+ or Ce3+-Mn2+ concentration based on energy transfer. Thus, the combination of blue, green and red emitting Ce3+, Tb3+ and Mn2+ generated white emission.

DOI： 10.1039/c7tc00941k

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Investigation of the Up-conversion Properties of Er-Yb-doped Calcium Tantalates with Various Ca/Ta Ratios Reviewed International journal

Sayaka Tamura, Michio Iwaoka, Yasushi Sato, Makoto Kobayashi, Masato Kakihana, Koji Tomita

Journal of Photopolymer Science and Technology   Vol. 30 ( 4 ) page： 507 - 512   2017

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TECHNICAL ASSOC PHOTOPOLYMERS,JAPAN  

Er3+/Yb3+ co-doped calcium tantalate up-conversion (UC) phosphors were synthesized via a parallel synthesis scheme using the gelable citrate complex method. Samples with various Ca/Ta atomic ratios were prepared, and their UC emission properties were compared. Under 980-nm near-infrared laser excitation, alpha-CazTa(2)O(7) : Er3+, Yb3+ showed an extremely weak UC emission intensity and CaTa4O11 : Er3+, Yb3+ demonstrated an excellent UC emission intensity. In addition, the local symmetry around the rare-earth dopant ions affected the UC luminescence properties.

DOI： 10.2494/photopolymer.30.507

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Exploration of New Oxynitride Phosphors Using a Vacuum-Pressure Sintering Furnace Invited

Hideki Kato, Hironori Sato, Takuya Yasunaga, Makoto Kobayashi, Masato Kakihana, Fumiyoshi Isobe

Shimadzu Review   Vol. 73 ( 3・4 ) page： 129-135   2016.12

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Language：Japanese  

Synthesis and Development of Titania with Controlled Structures Invited Reviewed

Makoto Kobayashi

Journal of the Ceramic Society of Japan   Vol. 124 ( 9 ) page： 863-869   2016.9

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Authorship：Lead author   Language：English  

DOI： 10.2109/jcersj2.16117

Screening of Er³⁺/Yb³⁺ Co-doped RE-Ta-O and RE-Nb-O (RE = Y, La, or Gd) Up-conversion Phosphors Reviewed International journal

Sayaka Tamura, Michio Iwaoka, Yasushi Sato, Makoto Kobayashi, Masato Kakihana, Koji Tomita

Chemistry Letters   Vol. 45 ( 8 ) page： 890 - 891   2016.8

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Upconversion (UC) phosphors comprising Er3+/Yb3+ co-doped rare-earth complex oxides, RExTayOz and RExNbyOz (RE = Y, La, or Gd), were synthesized via the gelable citrate complex method, and their UC emission properties were compared. This led to the discovery of an intense green-emitting UC phosphor, YTa7O19:Er3+/Yb3+, which is the first example of a YTa7O19 UC phosphor host material. Green UC emission obtained using optimum Er3+ and Yb3+ content was 20 times stronger than that obtained using a Y2O3 host.

DOI： 10.1246/cl.160413

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Anomalous Orange Light Emitting (Sr,Ba)₂SiO₄:Eu²⁺ Phosphors for Warm White LEDs Reviewed International journal

Dawei Wen, Hiroki Kuwahara, Hideki Kato, Makoto Kobayashi, Yasushi Sato, Takaki Masaki, Masato Kakihana

ACS Applied Materials & Interfaces   Vol. 8 ( 18 ) page： 11615 - 20   2016.5

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Phosphors with sufficient red emission component are necessary for warm white light-emitting diodes. In this work on (Sr,Ba)2(1-x)Eu2xSiO4 phosphors, (Sr,Ba)1.5Eu0.5SiO4 achieved 75% of an internal quantum efficiency under excitation by blue light. Surprisingly, the (Sr,Ba)1.5Eu0.5SiO4 exhibited orange emission, against the well-known traditional green-yellow emission of (Sr,Ba)2SiO4:Eu(2+). Moreover, the concentration quenching of Eu(2+) in (Sr,Ba)2SiO4 was abnormally unobvious. With the help of calculations based on the density functional theory, it was discovered that the distinct local environment of luminescence centers rather than usual explanation such as self-absorption or intensified crystal field splitting, is responsible to the interesting red shifts in excitation and emission spectra. The refinement analysis based on X-ray diffraction revealed that the unequal distribution of Eu(2+) to two crystallographic sites caused low concentration of Eu(2+) at the 9-coordination site, inhibiting the concentration quenching. The (Sr,Ba)1.5Eu0.5SiO4 phosphor has warmer emission than the commercial Y3Al5O12:Ce(3+). This study also promotes research on the effect of site occupancy and the local environment of luminescence centers.

DOI： 10.1021/acsami.6b02237

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Anisotropy in Conformation and Dynamics of a Glycolate Ion Near the Surface of a TiO₂ Rutile Crystal Between Its {001} and {110} Planes: A Molecular Dynamics Study Reviewed International journal

H. Nada, M. Kobayashi, M. Kakihana

Journal of Physical Chemistry C   Vol. 120 ( 12 ) page： 6502 - 6514   2016.3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A molecular dynamics simulation was conducted to elucidate the conformation and dynamics of a glycolate ion (CH2(OH)COO-) at the surface of a TiO2 rutile crystal. The simulation was performed for the {001} and {110} planes of the crystal. The results indicate that, for both planes, the conformation and dynamics of the ion are strongly dominated by a layered structure of water on the surface. The simulation suggests that the ion binds to the surface more stably on the {110} plane than on the {001} plane, and that the stable conformation of the ion at the surface differs between the planes: on the {110} plane the carboxyl group of the ion is preferentially oriented toward the surface, whereas on the {001} plane it is oriented toward liquid water. These simulation results are compared with the growth shapes of rutile crystals synthesized in the presence of glycolic acid, and the role of glycolate ions in controlling the morphology of rutile crystals is discussed.

DOI： 10.1021/acs.jpcc.5b11087

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Effect of Site Occupancy on Deep-red Emission from Eu²⁺-activated Ca₂SiO₄ Phosphor Reviewed International journal

Hiroki Kuwahara, Yasushi Sato, Hideki Kato, Makoto Kobayashi, Takaki Masaki, Masato Kakihana

Chemistry Letters   Vol. 45 ( 3 ) page： 321 - 323   2016.3

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Calcium silicate cosubstituted with Sr2+ and Eu2+ was studied in order to examine the relationship between emission characteristics and Eu2+ occupancy at two types of Ca sites (Ca(1n) and Ca(2n)). The results clearly indicate that red emission of the Ca2SiO4:Eu2+ phosphor is caused by Eu2+ substitution at the Ca(2n) site. In addition, red shift in emission of Eu(2n) occurs when large amounts of Eu were substituted.

DOI： 10.1246/cl.151145

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Self-assembly of polyethyleneamine-intercalated H₂Ti₂O₅ nanoparticles into spherical agglomerates Reviewed International journal

Makoto Kobayashi, Hideki Kato, Masato Kakihana

Journal of Materials Research   Vol. 31 ( 5 ) page： 564 - 572   2016.3

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

Although there are numerous reports on the synthesis of spherical materials, the development of new approaches remains important for theory construction to realize tailor-made synthesis of spherical materials. Herein, we report the synthesis of polydispersed spherical particles of H2Ti2O5 intercalated with a polyethyleneamine, such as an ethylenediamine, on the basis of a solvothermal treatment using concentrated polyethyleneamine aqueous solutions. The diameter of the micrometer-sized spheres enlarged with increasing amine concentration in the reaction solution. It was speculated that high ionic strength caused the self-assembly of polyethyleneamine-intercalated H2Ti2O5, resulting in the formation of spherical agglomerates. The spheres had a specific a surface area of 200 m(2) g(-1) and approximately 5 nm pores, and these values were controlled by amine concentration and treatment time. Conversion to single phase anatase and rutile without changes in spherical morphology was achieved by heat treatment. The present approach may assist with the design morphology of agglomerates.

DOI： 10.1557/jmr.2016.67

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Hydrothermal Synthesis of Barium Tantalate Nanosheet Photocatalyst and Its Water Splitting Activity Reviewed

Soichi Takasugi, Koji Tomita, Michio Iwaoka, Makoto Kobayashi, Hideki Kato, Masato Kakihana

Journal of the Society of Inorganic Materials, Japan   Vol. 23 ( 380 ) page： 25-29   2016

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Crystal Growth of Titania Polymorphs by Hydrothermal Method(<Special Issue>Topics of Crystal Growth Related to Water) Invited Reviewed International journal

Kobayashi Makoto, Kato Hideki, Kakihana Masato

Journal of the Japanese Association for Crystal Growth   Vol. 42 ( 4 ) page： 283-289   2016

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Control of crystal growth is rather important in the field of materials, because the shape directly affects their functional abilities. Our research group engages in hydrothermal synthesis of titanium dioxide, which is regarded as one of the representative ceramics, using water-soluble titanium complexes. The high chemical stability and peculiar molecule structures of these titanium complexes allowed us to use various compounds which play a role in control of crystal growth, resulting in the selective synthesis of four titanium dioxide polymorphs, that is, rutile, anatase, brookite and TiO_2(B), with a controlled shape. This paper summarizes our past study and reported researches on synthesis of titania polymorph crystals by classification of zero-, one-, two-, and three-dimensional structures.

DOI： 10.19009/jjacg.42.4_283

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Hydrothermal Synthesis of Barium Tantalate Nanosheet Photocatalyst and Its Water Splitting Activity Reviewed International journal

Soichi Takasugi, Koji Tomita, Michio Iwaoka, Makoto Kobayashi, Hideki Kato, Masato Kakihana

Journal of the Society of Inorganic Materials, Japan   Vol. 23 ( 380 ) page： 25-29   2016

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Graphene/M_xWO₃ (M = Na, K) nanohybrids with excellent electrical properties Reviewed International journal

Bin Liu, Shu Yin, Xiaoyong Wu, Yuhua Wang, Yunfang Huang, Jihuai Wu, Tohru Sekino, Junichi Matsushita, Soo Wohn Lee, Makoto Kobayashi, Masato Kakihana, Tsugio Sato

CARBON   Vol. 94   page： 309 - 316   2015.11

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Graphene/MxWO3 (M = Na, K) nanocomposites with different weight ratios were successfully synthesized using MBH4 as a reducing agent in aqueous solution, followed by crystallization of amorphous precursors under calcination in H-2 (5 vol.%)/N-2 atmosphere at 600 degrees C. The coupled samples showed good shielding properties in NIR wavelength range together with certain visible lights transparency. The as-prepared tungsten bronze nanoparticles are homogeneously anchored on graphene sheets, and the graphene/tungsten bronze nanocomposite showed an enhanced electrical conductivity with good shielding properties in the NIR range together with certain visible lights transparency. With the increment of graphene amount in the composites, the contact between the graphene sheets was enhanced, and the MxWO3 might enhance the charge transport properties of graphene by generating the short conductive path for electrons over the remained oxygenated functional groups. The synergistic effects could be observed in the composites. When 5 wt.% or more graphene were composed into MxWO3, the hybrid composite showed the higher electrical conductivity than those of uncoupled graphene and tungsten bronze alone. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.carbon.2015.06.072

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Large Redshifts in Emission and Excitation from Eu²⁺-Activated Sr₂SiO₄ and Ba₂SiO₄ Phosphors Induced by Controlling Eu²⁺ Occupancy on the Basis on Crystal-Site-Engineering Reviewed International journal

Yasushi Sato, Hiroki Kuwahara, Hideki Kato, Makoto Kobayashi, Takaki Masaki, Masato Kakihana

Optics and Photonics Journal   Vol. 5 ( 11 ) page： 326-333   2015.11

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8479

DOI： 10.4236/opj.2015.511031

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Photoluminescence Properties of Mn⁴+</sup>-activated Perovskite-type Titanates, La₂MTiO₆:Mn⁴⁺ (M = Mg and Zn) Reviewed International journal

Yohei Takeda, Hideki Kato, Makoto Kobayashi, Hisayoshi Kobayashi, Masato Kakihana

Chemistry Letters   Vol. 44 ( 11 ) page： 1541 - 1543   2015.11

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

It has been found that Mn4+-activated La2MTiO6 (M = Mg and Zn) functions as novel Eu-free phosphors for red emission in this work. La2MTiO6:Mn4+ exhibited emission with a peak at 710 nm under excitation by ultraviolet to blue light (300 550 nm). La2MgTiO6:Mn4+ exhibited stronger emission than La2ZnTiO6:Mn4+. The internal quantum yield of La2MgTiO6: Mn4+ was 58.7% under the excitation at 330 nm.

DOI： 10.1246/cl.150748

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A Facile One-Step Solvothermal Synthesis and Electrical Properties of Reduced Graphene Oxide/Rod-Shaped Potassium Tungsten Bronze Nanocomposite. Reviewed International journal

Bin Liu, Shu Yin, Yuhua Wang, Chongshen Guo, Xiaoyong Wu, Qiang Dong, Makoto Kobayashi, Masato Kakihana, Tsugio Sato

Journal of nanoscience and nanotechnology   Vol. 15 ( 9 ) page： 7305 - 10   2015.9

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Reduced graphene oxide (rGO)/rod-shaped potassium tungsten bronze nanocomposites with the different ratio were successfully synthesized by solvothermal reaction and followed by the reduction in H2(5 vol.%)/N2 atmosphere at 550 degrees C. The coupled samples showed excellent shielding ability of NIR light as well as certain visible lights transparency. The synergistic effects could be observed in the composites, i.e., when 15 wt% and 20 wt% of rGO which was fabricated by chemical reduction of graphene oxide, were composed into K(x)WO3, the composite showed the higher electrical conductivity than those of rGO and potassium tungsten bronze.

DOI： 10.1166/jnn.2015.10579

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Synthesis of picolinate-iron(III) compounds through an aqueous solution process Reviewed International journal

Junki Sato, Makoto Kobayashi, Hideki Kato, Eunsang Kwon, Masato Kakihana

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN   Vol. 123 ( 1441 ) page： 751 - 755   2015.9

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

A novel picolinate-iron(III) compound, Fe(C6H4NO2)(2)(OH) (1), was synthesized from an aqueous solution of a picolinate-iron(II) complex. Compound 1 was obtained by a thermal treatment of the picolinate-iron complex aqueous solution, whose pH was adjusted to 3-7, containing more than twice molar picolinic acid (Hpa) to Fe at 353K for 72 h. When the iron aqueous solution in the presence of more than six times molar Hpa to Fe at pH 2-5 was heated, Fe(C6H4NO2)(3)center dot H2O (2) appeared. Millimeter-sized yellow-green single crystals of 2 could be obtained by the heat treatment of the picolinate-iron aqueous solution, whose pH was adjusted to 3, with Fe2+:Hpa = 1: 10 at 373K for 72 h. Formation mechanism of 1 and 2 was also discussed through investigations of relationship between synthesis conditions and products. Our approach opens a promising new route for preparation of precursors for synthesis of high functional ceramics and development of new organic-inorganic hybrids. (C) 2015 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.123.751

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Novel Titanium Complexes with a Reversible Structural Change on Solvent Adsorption and Desorption Reviewed International journal

Makoto Kobayashi, Tatsuya Okuhara, Hideki Kato, Sota Sato, Masato Kakihana

Chemistry Letters   Vol. 44 ( 8 ) page： 1050 - 1052   2015.8

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Two novel pyrazine-2-carboxylate titanium complexes were synthesized from an aqueous solution (1) and 1 in N,N-dimethylformamide (DMF) (2). The structure of 2 was determined to be [Ti6O8(C4H3N2COO)(8)(C3H7NO)(4)]center dot 4C(3)H(7)NO center dot H2O by single-crystal X-ray analysis. Both complexes exhibited solvent adsorption desorption accompanying reversible structural change. 1 and 2 were compatible, and 1 was vital for the synthesis of 2. The degassed 1 showed gate adsorption property for water vapor.

DOI： 10.1246/cl.150393

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Discovery of Novel Delafossite-type Compounds Composed of Copper(I) Lithium Titanium with Photocatalytic Activity for H₂ Evolution under Visible Light Reviewed International journal

Hideki Kato, Tsuyoshi Fujisawa, Makoto Kobayashi, Masato Kakihana

CHEMISTRY LETTERS   Vol. 44 ( 7 ) page： 973 - 975   2015.7

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Novel delafossite-type compounds Cu(Li1/3Ti2/3)O-2 with 3R- and 2H-type structures have been discovered through the reaction between Li4Ti5O12 and Cu2O. Cu(Li1/3Ti2/3)O-2 is the first Cu(I)-titanate containing no d(n) (n = 1-9) metal ions. It has been found that Cu(Li1/3Ti2/3)O-2 with a band gap of 2.1 eV functions as a photocatalyst for H-2 evolution under visible light irradiation.

DOI： 10.1246/cl.150341

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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

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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

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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

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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

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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

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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

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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

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DOI： 10.1039/c5ta02482j

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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7678

DOI： 10.4236/opj.2013.36A003

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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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7677

DOI： 10.4236/opj.2013.36A002

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Development of a Novel Green Emitting Phosphate Phosphor KSrY(PO₄)₂:Eu⁺² Reviewed International journal

Akiko Saito, Hideki Kato, Makoto Kobayashi, Yasushi Sato, Masato Kakihana

Optics and Photonics Journal   Vol. 3 ( 6A ) page： 19-24   2013.10

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7679

DOI： 10.4236/opj.2013.36A004

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Synthesis of a Novel Bluish-Green Emitting Oxynitride Ca₃Al₈Si₄O₁₇N₄:Eu⁺² Phosphor in a CaAl_4-xSi_xO_7-xN_x Solid Solution Reviewed International journal

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

Optics and Photonics Journal   Vol. 3 ( 6A ) page： 29-33   2013.10

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7680

DOI： 10.4236/opj.2013.36A006

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Enhanced Dielectric Response Induced by Controlled Morphology in Rutile TiO₂ Nanocrystals Reviewed

Minoru Osada, Makoto Kobayashi, Masato Kakihana

Journal of the Ceramic Society of Japan   Vol. 121 ( 8 ) page： 593-597   2013.8

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7621

DOI： 10.2109/jcersj2.121.593

Luminescence properties of a novel green-emitting phosphate phosphor KSrY(PO₄)₂:Eu²⁺ Reviewed

Akiko Saito, Hideki Kato, Makoto Kobayashi, Masato Kakihana

IMID 2013 Digest     page： 261-261   2013.8

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Synthesis of new thiogallate phosphors (Ba_1-xSr_x)₄Ga₂S₇:Eu and their luminescence properties Reviewed

Kohei Takeuchi, Takahiko Hasegawa, Hideki Kato, Makoto Kobayashi, Masato Kakihana

IMID 2013 Digest     page： 260-260   2013.8

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Luminescence properties of a novel green-emitting phosphate phosphor KSrY(PO₄)₂:Eu²⁺ Reviewed International journal

Akiko Saito, Hideki Kato, Makoto Kobayashi, Masato Kakihana

IMID 2013 Digest     page： 261-261   2013.8

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Synthesis of new thiogallate phosphors (Ba_1-xSr_x)₄Ga₂S₇:Eu and their luminescence properties Reviewed International journal

Kohei Takeuchi, Takahiko Hasegawa, Hideki Kato, Makoto Kobayashi, Masato Kakihana

IMID 2013 Digest     page： 260-260   2013.8

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Synthesis of a LiCaPO₄:Eu²⁺ phosphor by a polymerizable complex method using a novel water-soluble phosphate precursor International journal

Minsung Kim, Makoto Kobayashi, Hideki Kato, Masato Kakihana

IMID 2013 Digest     page： 264 - 264   2013.8

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Photocatalytic Water Splitting over LaTa₇O₁₉ Composed of TaO₇ Pentagonal Bipyramids and TaO₆ Octahedra Reviewed International journal

Hideki Kato, Arisa Takeda, Makoto Kobayashi, Masato Kakihana

Chemistry Letters   Vol. 42 ( 7 ) page： 744 - 746   2013.7

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It has been found that cocatalyst-loaded LaTa7O19 with a band gap of 4.1 eV functions as a photocatalyst for water splitting under ultraviolet irradiation. The activity of Rh0.5Cr1.5O3-loaded LaTa7O19 prepared by a polymerizable complex method exhibited double of that prepared by a solid-state reaction. An apparent quantum yield of Rh0.5Cr1.5O3-loaded LaTa7O19 was determined to be 9.0% at 254 nm.

DOI： 10.1246/cl.130216

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Effect of carboxyl group on the visible-light photocatalytic activity of SrTiO3 nanoparticles Reviewed International journal

Huihui Li, Shu Yin, Yuhua Wang, Makoto Kobayashi, Satoko Tezuka, Masato Kakihana, Tsugio Sato

RESEARCH ON CHEMICAL INTERMEDIATES   Vol. 39 ( 4 ) page： 1615 - 1621   2013.4

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SrTiO3 nanoparticles modified with a carboxyl group were successfully prepared by microwave-assisted solvothermal reaction of SrCl2 center dot 6H(2)O and Ti(OC3H7)(4) in methanol-organic acid solution. The as-prepared products were characterized using X-ray diffraction (XRD), diffuse reflectance spectroscopy, and Fourier-transform infrared (FTIR) spectroscopy. The photocatalytic activity was determined by DeNO (x) ability using a mercury arc with filters to control irradiation wavelengths to &gt; 290, &gt; 400, and &gt; 510 nm. Nanoparticles of perovskite-type SrTiO3 were successfully synthesized above pH 12. The photocatalytic activity of SrTiO3 under visible-light (&gt; 510 nm) irradiation could be promoted by surface modification of SrTiO3 with the carboxyl group (-COO), especially from oleic acid.

DOI： 10.1007/s11164-012-0894-1

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水を溶媒に用いた機能性酸化物の低温合成のためのグリーンプレカーサーの開発 Invited Reviewed

小林亮, 垣花眞人

機能材料   Vol. 33 ( 1 ) page： 4-10   2013.1

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Control of Valence Band Potential and Photocatalytic Properties of Na_xLa_1-xTaO_1+2xN_2-2x Oxynitride Solid Solutions Reviewed International journal

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

Journal of Materials Chemistry A   Vol. 1 ( 11 ) page： 3667 - 3674   2013

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A series of oxynitride solid solutions, NaxLa1-xTaO1+2xN2-2x with x 0.1, 0.2, 0.25, 0.3, 0.5, 0.75 and 0.85, was successfully synthesized by nitridation of amorphous oxide precursors under an NH3 stream at 1273 K. The band gaps of the solid solutions increased with the Na content. Photoelectrochemical analysis was conducted to obtain information on the band potentials of the solid solutions. The valence band maxima of the solid solutions were at more positive potentials than that of LaTaON2 (x = 0). Solid solutions of NaxLa1-xTaO1+2xN2-2x with x = 0.20-0.85 exhibited photocatalytic activity for both H-2 and O-2 evolution under visible light irradiation in the presence of sacrificial reagents, while LaTaON2 had no activity for O-2 evolution. The achievement of O-2 evolution with these solid solutions is due to control of the valence band potential; therefore, control of the photocatalytic properties of LaTaON2 was achieved by the formation of solid solutions.

DOI： 10.1039/c3ta10257b

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Orange emission from (Ba1-XSrX)4Al 2S7:Eu2+ thioaluminate phosphors with visible light excitation Reviewed International journal

Takahiko Hasegawa, Hideki Kato, Yuji Takatsuka, Makoto Kobayashi, Hisanori Yamane, Masato Kakihana

ECS Journal of Solid State Science and Technology   Vol. 2 ( 2 ) page： R3107 - R3111   2013

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Solid solutions of (Ba1-XSrX)4Al 2S7 (X = 0.2 to 0.6) novel thioaluminate compound were synthesized, whose crystal structure was determined. The crystal structure of the (Ba1-XSrX)4Al2S7 solid solution is related to that of monoclinic Ba4Ga 2S7 consisting of isolated Ga2S7 units. However, the local structures around Ba/Sr in (Ba1-XSr X)4Al2S7, such as coordination number and one unusually long bond (d(Ba,Sr)-S 4 Å) in 7- and 8-coordinated (Ba,Sr)-S, are different from those in Ba4Ga 2S7. Eu2+-activated (Ba1-XSr X)4Al2S7 exhibited orange emission with a peak maximum at 594 nm and a corresponding excitation band at 300 to 550 nm. This is the first report of an orange phosphor in the thioaluminate system. The thermal quenching of luminescence in the (Ba1-XSr X)4Al2S7:Eu2+ phosphor was comparable to that in a conventional Y3Al5O 12:Ce3+ phosphor. © 2012 The Electrochemical Society.

DOI： 10.1149/2.019302jss

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Fabrication of SrTiO3 exposing characteristic facets using molten salt flux and improvement of photocatalytic activity for water splitting Reviewed International journal

Hideki Kato, Makoto Kobayashi, Michikazu Hara, Masato Kakihana

CATALYSIS SCIENCE & TECHNOLOGY   Vol. 3 ( 7 ) page： 1733 - 1738   2013

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Flux treatment using various molten salts was performed for SrTiO3 powders. Morphology of SrTiO3 crystals obtained by the flux treatment strongly depended on the kinds of molten salts used. Large cubic crystals exposing {100} facets with a size of 5-6 mm were obtained by the flux treatment with LiCl whereas truncated cubes exposing {100} and {110} facets with a size of 200-400 nm were obtained when NaCl or SrCl2 was used as a flux reagent. In contrast, the flux treatment with KCl gave characteristic shaped crystals with a size of 300 nm. Electron microscope observation and electron diffraction analysis revealed that the crystals treated with the KCl flux expose {100}, {120}, and {121} facets. SrTiO3 treated with the KCl flux exhibited higher activity by 20 times than the non-flux-treated sample. Thus, a remarkable improvement of activity has been achieved by the fabrication of SrTiO3 crystals exposing high-index facets, {120} and {121}, using the KCl flux.

DOI： 10.1039/c3cy00014a

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Enhancement of luminescence properties of a KSrPO₄:Eu²+ phosphor prepared using a solution method with a water-soluble phosphate oligomer Reviewed International journal

Minsung Kim, Makoto Kobayashi, Hideki Kato, Masato Kakihana

JOURNAL OF MATERIALS CHEMISTRY C   Vol. 1 ( 36 ) page： 5741 - 5746   2013

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A novel phosphate raw material having an oligomeric structure with desirable stability and solubility under aqueous conditions was prepared via an esterification reaction between H3PO4 and ethylene glycol under reflux. A blue emitting KSrPO4:Eu2+ phosphor with high luminescence was subsequently synthesized using a polymerizable complex (PC) method with the prepared phosphate oligomers as a source of P. KSrPO4:Eu2+ thus prepared exhibited higher emission intensity than samples prepared using a solid state reaction method or the PC method using H3PO4. This high luminescence was attributed to the excellent homogeneity of the constituents in the sample. It was found that KSrPO4 doped with more than 3 mol% of Eu2+ showed a new low-energy emission band at approximately 480 nm, in addition to the known emission band at 428 nm. This new feature was speculated to be derived from disordering of K and Sr ions caused by the high homogeneity of the constituents. Moreover, it was confirmed that thermal quenching of emission at 428 nm above 423 K was recovered in samples doped with more than 7% of Eu.

DOI： 10.1039/c3tc31121j

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Photocatalytic activities of Cu_3xLa_1-xTa₇O₁₇ solid solutions for H₂ evolution under visible light irradiation Reviewed International journal

Hideki Kato, Arisa Takeda, Makoto Kobayashi, Michikazu Hara, Masato Kakihana

Catalysis Science & Technology   Vol. 3 ( 12 ) page： 3147 - 3154   2013

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Development of new visible-light-driven oxide photocatalysts for H2 evolution was conducted with a concept of formation of solid solutions containing Cu(I) ions. Band gaps of Cu3xLa1-xTa7O19 solid solutions were 2.57-2.71 eV being remarkably narrower than that of LaTa7O19 (x = 0, 4.14 eV). The remarkable narrowing of the band gaps was due to the contribution of Cu 3d orbitals to valence bands. The solid solutions were capable of photocatalytic H-2 evolution under visible light irradiation in the presence of methanol as an electron donor. Interestingly, the solid solutions with x = 0.2-0.8 showed higher activities than that of a native Cu(I)-tantalate, Cu3Ta7O19 (x = 0). Among the solid solutions, the x = 0.6 sample, Cu1.8La0.4Ta7O19, exhibited the highest activity. The apparent quantum yield of the optimized photocatalyst was 0.48% at 420 nm. Moreover, the good stability of Cu(I) ions in the solid solutions was proven through the investigation of photocatalytic properties and the XPS analysis. Thus, new visible-light-driven oxide photocatalysts capable of H-2 evolution were developed by the formation of the Cu(3x)La(1-x)Ta(7)O19 solid solutions.

DOI： 10.1039/c3cy00557g

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Synthesis of spindle and square bipyramid-shaped anatase-type titanium dioxide crystals by a solvothermal method using ethylenediamine Reviewed International journal

Makoto Kobayashi, Hideki Kato, Masato Kakihana

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN   Vol. 120 ( 1407 ) page： 494 - 499   2012.11

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Morphological control as well as formation of nanoparticles of anatase-type titanium dioxide has been achieved by a solvothermal treatment of a water-soluble citratoperoxotitanium (CPT) complex using ethylenediamine (EDA) as a key solvent in the presence of a given amount of water. When the EDA concentration in the whole solvent (EDA + H2O) remained low less than 12 M, the powder obtained after the solvothermal treatment consisted of spindle-like anatase particles. With an increase of the EDA concentration in the solvent, the shape of the obtained particles changed from spindle to square bipyramid. When another water-soluble oxoglycolatoperoxotitanate complex or TiCl4 was used as a starting source of Ti, similar shaped anatase particles could be obtained by a careful choice of synthetic conditions. Using a mixed solvent of EDA and water, sheet-like titanic acid was produced as an intermediate phase, regardless of the EDA concentration. Therefore, the formation of anatase in the current system may take place through dissolution-recrystallization of titanic acid. The formation of square bipyramidal anatase particle achieved in the present study is not agreement with a reported theoretical calculation of equilibrium phase, because the calculation reveals that truncated square bipyramid-like anatase is obtained under an acidic condition and spindle-like anatase was formed under a basic condition. An adsorption of EDA on particle surface and the pH of the solvent may contribute to the achievement of morphological control. (C)2012 The Ceramic Society of Japan All rights reserved.

DOI： 10.2109/jcersj2.120.494

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Synthesis of new thioaluminate phosphors (Ba_1-XSr_X)₄Al₂S₇:Eu and their luminescence properties Reviewed

Takahiko Hasegawa, Makoto Kobayashi, Hideki Kato, Hisanori Yamane, Masato Kakihana

Technical digest of the 12th International Meeting on Information Display     page： 640-641   2012.8

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Impact of synthesis methodology on the optimization of photoluminescence emission intensity of NaBaScSi₂O₇:Eu²⁺ phosphor Reviewed International journal

Sudeshna Ray, Kenji Toda, Shinnosuke Kamei, Tadashi Ishigaki, Kazuyoshi Uematsu, Mineo Sato, Hideki Kato, Makoto Kobayashi, Masato Kakihana

Technical digest of the 12th International Meeting on Information Display     page： 128 - 129   2012.8

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Synthesis of the new compound in a Na-Sc-Si-O system and Luminescence properties activated by Eu²⁺ Reviewed International journal

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

Technical digest of the 12th International Meeting on Information Display     page： 638-639   2012.8

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Synthesis of new thioaluminate phosphors (Ba_1-xSr_x)₄Al₂S₇:Eu and their luminescence properties Reviewed International journal

Takahiko Hasegawa, Makoto Kobayashi, Hideki Kato, Hisanori Yamane, Masato Kakihana

Technical digest of the 12th International Meeting on Information Display     page： 640-641   2012.8

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Synthesis of KSrPO₄:Eu²⁺ Phosphor with High Luminescence Property Using a Water-Soluble Phosphorus Precursor Reviewed International journal

Minsung Kim, Makoto Kobayashi, Hideki Kato, Masato Kakihana

Technical digest of the 12th International Meeting on Information Display     page： 130-131   2012.8

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Preparation of Hollow TiO² Spheres of the Desired Polymorphs by Layer-by-Layer Assembly of a Water-Soluble Titanium Complex and Hydrothermal Treatment Reviewed International journal

Kiyofumi Katagiri, Hitoshi Inami, Kunihito Koumoto, Kei Inumaru, Koji Tomita, Makoto Kobayashi, Masato Kakihana

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY   ( 20 ) page： 3267 - 3272   2012.7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

A facile approach, based on the polyelectrolyte-mediated electrostatic adsorption of a water-soluble titanium complex on colloid templates and hydrothermal treatment, is presented for the formation of hollow TiO2 spheres of the desired polymorphs. The coreshell particles were formed by the alternate deposition of titaniumglycolate complex 1 and positively charged polyelectrolyte, poly(allylamine hydrochloride) (PAH) on spherical polystyrene (PS) templates by utilizing electrostatic interactions for shell formation. Hollow spheres formed with the polyionic complex of 1 and PAH were obtained by removal of the PS templates. Formation of the polyionic complex affected the crystallization of TiO2 from 1 by hydrothermal treatment. Hollow spheres of brookite and anatase were obtained by hydrothermal treatment at pH 4 and 10, respectively. The approach presented here can be exploited for the fabrication of novel advanced titania-based materials with desired structures and polymorphs.

DOI： 10.1002/ejic.201200421

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Morphology-Controlled Synthesis of W₁₈O₄₉ Nanostructures and Their Near-Infrared Absorption Properties Reviewed International journal

Chongshen Guo, Shu Yin, Mei Yan, Makoto Kobayashi, Masato Kakihana, Tsugio Sato

Inorganic chemistry   Vol. 51 ( 8 ) page： 4763 - 71   2012.4

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The morphology-controlled synthesis and near-infrared (NIR) absorption properties of W(18)O(49) were systematically investigated for the application of innovative energy-saving windows. Various morphologies of W(18)O(49), such as nanorods, nanofibers, nanograins, nanoassembles, nanoplates, and nanoparticles, with various sizes were successfully synthesized by solvothermal reactions using organic alcohols as reaction media and WCl(6), W(EtO)(6), and WO(3) solids as the tungsten source. W(18)O(49) nanorods of less than 50 nm in length showed the best optical performance as an effective solar filter, which realized high transmittance in the visible region as well as excellent shielding properties of NIR light. Meanwhile, the W(18)O(49) nanorods also exhibited strong absorption of NIR light and instantaneous conversion of the absorbed photoenergy to the local heat.

DOI： 10.1021/ic300049j

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Hydrothermal synthesis of brookite-type titanium dioxide with snowflake-like nanostructures using a water-soluble citratoperoxotitanate complex Reviewed International journal

Makoto Kobayashi, Valery Petrykin, Koji Tomita, Masato Kakihana

Journal of Crystal Growth   Vol. 337 ( 1 ) page： 30 - 37   2011.12

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Hydrothermal synthesis of brookite-type titanium dioxide was performed with excellent reproducibility using an aqueous NH3 solution of a water-soluble citratoperoxotitanate (CPT) complex. X-ray diffraction confirmed that the brookite phase was formed by hydrothermal treatment of the CPT complex in NH3 solution with a concentration of more than 6.5 wt%, whereas single phase anatase was obtained when distilled water without any additives was applied as the solvent. The aspect ratios of the obtained rod-like brookite particles increased from 5 up to 20 with an increase of the NH3 concentration. Transmission electron microscopy and selected area electron diffraction measurements provided evidence that the growth of the brookite particles is along the c-axis. Hydrothermal treatment of the CPT complex at high NH3 concentrations resulted in the formation of agglomerated brookite particles with unusual shapes, where many rod-like particles were branched around a somewhat longer central particle, and the side view of the agglomerated particles revealed two-dimensional crystal growth within a given restricted plane. The multi-needle agglomerate of particles was snowflake shaped. The reason for the formation of brookite with this unique morphology may be attributed to an intrinsic character of the CPT complex itself, although the mechanism is yet to be clarified. © 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2011.09.046

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Hydrothermal synthesis of hierarchical TiO₂ microspheres using a novel titanium complex coordinated by picolinic acid Reviewed International journal

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

Journal of the Ceramic Society of Japan   Vol. 119 ( 1390 ) page： 513 - 516   2011

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Phase- and morphology-control of TiO2 was performed by a facile hydrothermal method using a novel water-soluble titaniumpicolinato complex as a precursor. Single-phase rutile or brookite type titania can be obtained by tailoring the pH of the complex solution. Rutile with a hierarchical microstructure was synthesized using an excess amount of ligand as an additive and the final product consisted of microspheres with mesopores formed by a self-assembly of nanorods. The anisotropic growth of nanorods with a high aspect ratio was explained by a capping mechanism. © 2011 The Ceramic Society of Japan.

DOI： 10.2109/jcersj2.119.513

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Application of Water-Soluble Titanium Complexes as Precursors for Synthesis of Titanium-Containing Oxides via Aqueous Solution Processes Invited Reviewed International journal

Masato Kakihana, Makoto Kobayashi, Koji Tomita, Valery Petrykin

BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN   Vol. 83 ( 11 ) page： 1285 - 1308   2010.11

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

The growing significance of nanocrystalline inorganic functional materials in the fields of catalysis, electronics, and energy conversion together with the increasing demand of the society for safer, softer, and "greener" technologies has drawn considerable attention of the researchers toward water-based solution processes for synthesis of such materials. In this respect complex oxides, containing d(0)-transition metals, such as Ti, Nb, Ta, or Si represent an outstanding challenge. for materials chemists due to the extremely narrow range or almost complete absence of suitable precursor compounds compatible with aqueous systems. In the recent 10 years, a remarkable progress has been achieved in the development of new water-soluble complexes of titanium and considerable experience was accumulated in the application of these compounds for synthesis of nanocrystalline titanium-containing materials. The essential knowledge of coordination chemistry of such water-soluble titanium complexes is reviewed in this work, which succeeded to identify the key structural features responsible for stability of the compounds against hydrolysis and to provide guidelines for synthesis of these complexes. Finally, an extensive overview of highly selective aqueous solution based synthesis of TiO2 polymorphs as well as complex oxide materials with the help of the novel water-soluble titanium complexes is provided.

DOI： 10.1246/bcsj.20100103

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酸化チタンのテーラメイド合成 Invited Reviewed

小林亮, 垣花眞人

現代化学   Vol. 465 ( 12 ) page： 57-62   2009.11

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Selective Synthesis of TiO₂ Polymorphs by Hydrothermal Method using New Water-Soluble Titanium Complexes Invited Reviewed International journal

Masato Kakihana, Makoto Kobayashi, Valery Petrykin, Koji Tomita

Journal of the Japan Society of Powder and Powder Metallurgy   Vol. 56 ( 4 ) page： 188-193   2009.4

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A panel of new stable and water soluble complexes of titanium (IV) with natural hydroxy-carboxylic acids such as citric, tartaric, lactic or glycolic acid as ligands was developed. A typical structure of these complex ions includes a peroxo-group, and a hydroxy-carboxylic acid molecule attached to the metal ion by carboxylic and hydroxylic groups to form stable species. The tight coordination and negative charge of complex ions are responsible for stability of these new compounds in water solutions in a wide range of temperatures and pH. Use of natural non-toxic ligands and ammonium as counterions make such titanium compounds convenient reagents for "green" synthesis of titanium containing materials by aqueous solution methods.<BR>The architecture of titanium complexes includes structural motifs of different polymorphic forms of TiO<SUB>2</SUB>, which allows for application of these compounds as building blocks (tecton) for synthesis of titania with different crystal structures by a simple hydrothermal processes. In this way anatase, rutile, TiO<SUB>2</SUB>(B) and brookite were prepared in a reproducible and highly selective way. For the first time TiO<SUB>2</SUB>(B) and brookite were synthesized as single phase nano-crystals by a "one-pot" hydrothermal process, and their outstanding photo-catalytic activities were revealed.

DOI： 10.2497/jjspm.56.188

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Hydrothermal synthesis of brookite type TiO2 photocatalysts using a water-soluble Ti-complex coordinated by ethylenediaminetetraacetic acid Reviewed International journal

Yusuke Morishima, Makoto Kobayashi, Valery Petrykin, Shu Yin, Tsugio Sato, Masato Kakihana, Koji Tomita

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN   Vol. 117 ( 1363 ) page： 320 - 325   2009.3

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

Nanocrystalline brookite titanium oxide was prepared by hydrothermal treatment of a water-soluble titanium complex with ethylenediaminetetraacetic acid (EDTA). In this work, we examined the effect of synthesis conditions such as reaction time, titanium concentration and solution pH on the brookite phase formation and its photocatalyitic performance. It was found that hydrothermal treatment of the titanium complex may yield anatase and brookite phases, and their ratio can be varied depending on titanium concentration. Single phase brookite could be prepared when titanium concentration in the starting solution was higher than 0.25 mol/dm(3), while lower concentration favors formation of anatase. Remarkably, brookite could be synthesized from the Ti-EDTA complex in the wide range of pH including both acidic and basic media. The samples prepared from Ti-EDTA complex demonstrated higher photocatalytic activity in terms of NO gas decomposition than the brookite powders synthesized from Ti-glycolate complex or commercial TiO2 photocatalyst P25. Higher photocatalytic activity of powders obtained from Ti-EDTA complex aqueous solution is explained by higher surface area of smaller but well-crystallized brookite particles that can be achieved when this new titanium complex is employed. (C) 2009 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.117.320

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Photocatalytic activity of nanocrystalline TiO2(B) synthesized from titanium glycolate complex by hydrothermal method Reviewed International journal

Kazuhiro Yamamoto, Hironori Shimoita, Koji Tomita, Kazumi Fujita, Makoto Kobayashi, Valery Petrykin, Masato Kakihana

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN   Vol. 117 ( 1363 ) page： 347 - 350   2009.3

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

The metastable phase of TiO2(B), one of the polymorphs of titanium dioxide (TiO2), was prepared by a hydrothermal treatment of a titanium glycolate complex ([Ti-4(C2H2O3)(4)(C2H3O3)(2)(O-2)(4)O-2](6-)) at 473 K for 1-72 h in the presence of H2SO4. Characterization by X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that the obtained samples were composed of single phase TiO2(B) and the particles had plate-like morphology. After post-synthetic hydrothermal crystal growth (PHCG) applied to the as-prepared sample, thicker plate-like shaped particles were obtained. The photocatalytic activities of the samples obtained by the hydrothermal treatment and after the subsequent PHCG were evaluated in terms of methanol decomposition. (C) 2009 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.117.347

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チタン錯体水溶液からの酸化チタン光触媒の合成 Invited Reviewed

小林亮, Petykin Valery, 垣花眞人, 冨田恒之

化学工業   Vol. 60 ( 1 ) page： 71-77   2009.1

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Hydrothermal Synthesis and Photocatalytic Activity of Whisker-Like Rutile-Type Titanium Dioxide Reviewed International journal

Makoto Kobayashi, Valery Petrykin, Masato Kakihana, Koji Tomita

JOURNAL OF THE AMERICAN CERAMIC SOCIETY   Vol. 92 ( 1 ) page： S21 - S26   2009.1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL PUBLISHING, INC  

Nanowhiskers of rutile-type titanium dioxide (TiO(2)) were synthesized by a simple hydrothermal treatment of a water-soluble titanium-glycolate complex at 473 K. The aspect ratio of the obtained rutile particles could be controlled by changing the concentration of the glycolic acid additive in the starting aqueous solution of the titanium complex. According to high-resolution transmission electron microscopy, whisker-like nanoparticles grow along the c-axis of rutile, the side facets of which are (110), (-110), (1-10), and (-1-10). Glycolic acid controls promotion of the rutile particles in the specified direction due to its preferred adsorption on the titanium-rich facets. Evaluation of the photocatalytic activity of the synthesized TiO(2) was performed in terms of decomposition of oxalic acid in an aqueous system under ultraviolet irradiation. It turned out that this particular whisker-like shape is responsible for the tremendous enhancement of rutile photocatalytic activity, and even rutile samples with low surface area demonstrated photocatalytic performance comparable with one of the best nanosized anatase photocatalytic materials. Therefore, it can be concluded that the (110) rutile facet plays an important role in the photocatalytic oxidation reaction, and that it exhibits higher photocatalytic activity than the (001) facet in the decomposition of oxalic acid.

DOI： 10.1111/j.1551-2916.2008.02641.x

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Synthesis of TiO2(B) using glycolato titanium complex and post-synthetic hydrothermal crystal growth of TiO2(B) Reviewed International journal

K. Yamamoto, K. Tomita, K. Fujita, M. Kobayashi, V. Petrykin, M. Kakihana

Journal of Crystal Growth   Vol. 311 ( 3 ) page： 619 - 622   2009.1

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

Titanium dioxide (TiO2(B), one of metastable polymorphs of TiO2 was prepared by hydrothermal reaction of glycolato peroxotitanium complex ([Ti-4(C2H2O3)(4)(C2H3O3)(2)(O-2)(2)](6) in the presence of H2SO4 as an additive. Characterization by X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM) revealed that the obtained powders were single-phase TiO2(B) with rod-like shape, Particle size and aspect ratio of TiO2(B) can be controlled by post-synthetic hydrothermal crystal growth (PHCG) of the as-prepared powder sample. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2008.09.041

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Selective synthesis of nano-crystalline TiO₂ polymorphs from new water-soluble titanium complexes Reviewed

Masato Kakihana, Makoto Kobayashi, Valery Petrykin, Koji Tomita

Acta Crystallographica Section A   ( 64 ) page： C20   2008.8

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Direct synthesis of brookite-type titanium oxide by hydrothermal method using water-soluble titanium complexes Reviewed International journal

Makoto Kobayashi, Koji Tomita, Valery Petrykin, Masahiro Yoshimura, Masato Kakihana

Journal of Materials Science   Vol. 43 ( 7 ) page： 2158 - 2162   2008.4

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

It was demonstrated that brookite-type titanium oxide can be directly synthesized by the hydrothermal treatment of novel water-soluble titanium complexes under basic conditions in the presence of an additive. In particular, single-phase brookite was synthesized from the titanium-glycolate complex at a pH of about 10 in the presence of excess NH(3) aqueous solution or ethylenediamine, and powder thus obtained consisted of rod-like nanosized particles. It was suggested that the structures of titanium complexes are important for the formation of brookite.

DOI： 10.1007/s10853-007-1912-3

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New water-soluble complexes of titanium with amino acids and their application for synthesis of TiO₂ nanoparticles Reviewed International journal

Makoto Kobayashi, Valery Petrykin, Koji Tomita, Masato Kakihana

Journal of the Ceramic Society of Japan   Vol. 116 ( 1352 ) page： 578 - 583   2008.4

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

We prepared two new water-soluble complexes of titanium with L-serine and L(-)-threonine amino acids. It was demonstrated that these compounds can be outstanding precursors for a hydrothermal synthesis of nanocrystalline TiO2. The obtained powders were composed of anatase or a mixture of anatase and brookite. Particles diameters were -10 nm and BET surface areas were -120 m(2)/g. The powder composed of anallase and brookite synthesized by hydrothermal treatment of the titanium-threonine complex aqueous solution at 200 degrees C for 24 h exhibited higher photocatalytic activity for oxalic acid oxidation than the commercial anatase-type TiO2 photocatalyst (ST-01, Ishihara Sangyo Kaisya, average diameter: 7 nm, specific surface area: 257.5 m(2)/g). (c) 2008 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.116.578

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Hydrothermal synthesis of TiO₂ nano-particles using novel water-soluble titanium complexes Reviewed International journal

Koji Tomita, Makoto Kobayashi, Valery Petrykin, Shu Yin, Tsugio Sato, Masahiro Yoshimura, Masato Kakihana

Journal of Materials Science   Vol. 43 ( 7 ) page： 2217 - 2221   2008.4

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Hydrothermal treatment of a series of water-soluble titanium complexes resulted in the formation of TiO2. Rutile, anatase or a mixture of both can be synthesized by varying the ligands. The titania obtained was composed of nano-sized particles with large specific surface areas. These TiO2 powders exhibited high photocatalytic activity for NO x decomposition. In particular, they demonstrated higher activity than P25 (Degussa) under visible-light irradiation. © 2007 Springer Science+Business Media, LLC.

DOI： 10.1007/s10853-007-2113-9

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INOR 1052-Synthesis of oxide materials using new water soluble titanium and tantalum complexes Reviewed International journal

Valery Petrykin, Makoto Kobayashi, Koji Tomita, Masato Kakihana

ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY   Vol. 235   2008.4

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Microwave-assisted hydrothermal synthesis of brookite nanoparticles from a water-soluble titanium complex and their photocatalytic activity Reviewed International journal

Yusuke Morishinia, Makoto Kobayashi, Valery Petrykin, Masato Kakihana, Koji Tomita

Journal of the Ceramic Society of Japan   Vol. 115 ( 1348 ) page： 826 - 830   2007.12

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

Nanoparticles of brookite titanium oxide were prepared by microwave-assisted hydrothermal (MH) method at 200 degrees C (heating time 5 min) for 0-60 minutes starting from the titanium peroxo glycolate complex in basic solution. The effect of microwave heating on the morphology of the brookite particles was examined. The samples were characterized by X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM). It was found that all powders were composed of single phase brookite and contained two different types of particles. The activity in photodecomposition of oxalic acid by the samples prepared using MH method was higher than activities of brookite nanoparticles synthesized by the conventional hydrothermal method.

DOI： 10.2109/jcersj2.115.826

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Morphology control of rutile nanoparticles in a hydrothermal synthesis from water-soluble titanium complex aqueous solution Reviewed International journal

Makoto Kobayashi, Valery Petrykin, Masato Kakihana, Koji Tomita

Journal of the Ceramic Society of Japan   Vol. 115 ( 1348 ) page： 835 - 839   2007.12

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

Single phase rutile was synthesized by a simple hydrothermal treatment of an aqueous titanium glycolate complex solution at 200 degrees C for 24 h. The obtained sample was composed of 50 x 150 nm rod-like nanoparticles. The aspect ratio of the prepared particles could be controlled by adding glycolic acid or lactic acid to reaction solution. Up to 30 x 2000 nm whisker-like particles could be obtained. The hydroxycarboxylic acids favor development of specific crystal facets and allow to control the aspect ratio of the rutile nanoparticles. We also proposed a model, which explains formation of anatase and rutile, and disappearance of anatase particles during rutile crystals development.

DOI： 10.2109/jcersj2.115.835

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One-step synthesis of TiO₂(B) nanoparticles from a Water-Soluble titanium complex Reviewed International journal

Makoto Kobayashi, Valery V. Petrykin, Masato Kakihana, Koji Tomita, Masahiro Yoshimura

Chemistry of Materials   Vol. 19 ( 22 ) page： 5373-5376   2007.10

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DOI： 10.1021/cm071370q

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ゾル－ゲルコーティング材料としての新規水溶性チタン錯体 Invited Reviewed

垣花眞人, 冨田恒之, 小林亮

化学工業   Vol. 57 ( 12 ) page： 13-19   2006.12

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Hydrothermal synthesis of nanosized titania photocatalysts using novel water-soluble titanium complexes Reviewed International journal

Makoto Kobayashi, Koji Tomita, Valery Petrykin, Syu Yin, Tsugio Sato, Masahiro Yoshimura, Masato Kakihana

Solid State Phenomena   Vol. 124-126   page： 723-726   2006.9

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DOI： 10.4028/www.scientific.net/SSP.124-126.723

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A water-soluble titanium complex for the selective synthesis of nanocrystalline brookite, rutile, and anatase by a hydrothermal method. Reviewed International journal

Koji Tomita, Valery Petrykin, Makoto Kobayashi, Motoo Shiro, Masahiro Yoshimura, Masato Kakihana

Angewandte Chemie International Edition   Vol. 45 ( 15 ) page： 2378 - 81   2006.4

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DOI： 10.1002/anie.200503565

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水溶液から酸化チタンを作る Invited Reviewed

小林亮, 冨田恒之, 垣花眞人

色材協会コラム   ( 20 ) page： 1   2006

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水溶性プロセスを利用したセラミックスの合成 Invited Reviewed

冨田恒之, 小林亮, 垣花眞人

未来材料   Vol. 5 ( 10 ) page： 37 - 43   2005.10

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Language：Japanese