Faculty Profiles - KOBAYASHI Makoto

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

Ferroelectricity in CsPb2Nb3O10 and exfoliated 2D nanosheets Reviewed International coauthorship

Yan Li, Masanari Shimada, Makoto Kobayashi, Eisuke Yamamoto, Ruben Canton-Vitoria, Xiaoyan Liu, Minoru Osada

Dalton Transactions Vol. 53 ( 45 ) page： 18122 - 18127 2024

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

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

Gigantic Thermal Shielding in 2D Oxide Nanosheets. Reviewed International journal

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

ACS nano Vol. 17 ( 12 ) page： 11396 - 11405 2023.6

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

Thermal shielding materials that can block near-infrared (NIR) light from the sunlight while maintaining visible transparency have become increasingly important from an energy-saving perspective. Here, we demonstrate a gigantic NIR shielding by an engineered plasmonic material based on a two-dimensional (2D) polytungstate (Cs4-xW11O35-d). Starting from a charge-neutral polytungstate (Cs4W11O35), we synthesize charge-imbalanced 2D nanosheets (Cs4-xW11O35-d) that undergo an unusual structural change with the semiconductor-to-metal transition in a reduced atmosphere. Layer-by-layer engineering of the 2D nanosheets enables a plasmon-induced enhancement of the NIR reflectance (>53%) with a high visible transparency (>71%), realizing high-performance thermal shielding. Our approach offers a solution for future thermal management technology.

DOI： 10.1021/acsnano.3c00815

Ultrahigh Energy Storage in 2D High-κ Perovskites. Reviewed International journal

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

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

Dielectric capacitors have greater power densities than batteries, and, unlike batteries, they do not utilize chemical reactions during cycling. Thus, they can become ideal, safe energy storage devices. However, dielectric capacitors yield rather low energy densities compared with other energy storage devices such as batteries and supercapacitors. Here, we present a rational approach for designing ultrahigh energy storage capacitors using two-dimensional (2D) high-κ dielectric perovskites (Ca2Nam-3NbmO3m+1; m = 3-6). Individual Ca2Nam-3NbmO3m+1 nanosheets exhibit an ultrahigh dielectric strength (638-1195 MV m-1) even in the monolayer form, which exceeds those of conventional dielectric materials. Multilayer stacked nanosheet capacitors exhibit ultrahigh energy densities (174-272 J cm-3), high efficiencies (>90%), excellent reliability (>107 cycles), and temperature stability (-50-300 °C); the maximum energy density is much higher than those of conventional dielectric materials and even comparable to those of lithium-ion batteries. Enhancing the energy density may make dielectric capacitors more competitive with batteries.

DOI： 10.1021/acs.nanolett.3c00079

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

Makoto Kobayashi, Tsubasa Tasaka, Eisuke Yamamoto, Minoru Osada

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

Pseudo-Topotactic Transformation from Oxide Nanosheets to Amorphous Nanosheets Reviewed Open Access

Hikaru Sugimoto, Makoto Kobayashi, Eisuke Yamamoto, Minoru Osada

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

Composite design of two-dimensional inorganic nanosheets for flexible energy storage capacitors Open Access

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

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN Vol. 131 ( 4 ) page： 77 - 82 2023.4

Language：English Publishing type：Research paper (scientific journal) Publisher：The Ceramic Society of Japan

We present a new approach for designing flexible energy storage capacitors using two-dimensional (2D) inorganic nanosheets. 2D dielectric Ca2Nb3O10 nanosheet and ferroelectric poly(vinylidene fluoride) (PVDF) were selected as model material systems. Langmuir–Blodgett deposition was utilized for layer-by-layer engineering of (Ca2Nb3O10/PVDF) nanocomposite films on an indium tin oxide (ITO)-coated polyethylene terephthalate (PET) substrate. Such a new composite design realized the simultaneous improvement of energy density (∼7 J cm−3) and efficiency (∼78 %) even in the ultrathin form (∼20 nm) on the ITO-coated PET substrate. Nanosheet-based flexible capacitors also maintained a stable performance even after 104 times bending cycles. These results indicate that our nanosheet approach is of technological importance for exploring new flexible dielectric capacitors.

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

Free-Standing Molecularly Thin Amorphous Silica Nanosheets Reviewed Open Access

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

Small Vol. 19 ( 22 ) page： 2300022 - 2300022 2023.2

Molecularly Thin BaTiO₃ Nanosheets with Stable Ferroelectric Response Reviewed International coauthorship Open Access

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

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

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

Language：English Publishing type：Research paper (scientific journal) Publisher：Springer Science and Business Media LLC

<jats:title>Abstract</jats:title><jats:p>Desired electrode patterning on two-dimensional (2D) materials is a foremost step for realizing the full potentials of 2D materials in electronic devices. Here, we introduce an approach for damage-free, on-demand manufacturing of 2D material devices using light-emitting diode (LED) lithography. The advantage of this method lies in mild photolithography by simply combining an ordinary optical microscope with a commercially available LED projector; the low-energy red component is utilized for optical characterization and alignment of devices, whereas the high-energy blue component is utilized for photoresist exposure and development of personal computer designed electrode patterns. This method offers maskless, damage-free photolithography, which is particularly suitable for 2D materials that are sensitive to conventional lithography. We applied this LED lithography to device fabrication of selected nanosheets (MoS<jats:sub>2</jats:sub>, graphene oxides and RuO<jats:sub>2</jats:sub>), and achieved damage-free lithography of various patterned electrodes with feature sizes as small as 1–2 μm. The LED lithography offers a useful approach for cost-effective mild lithography without any costly instruments, high vacuum, or complex operation.</jats:p>

DOI： 10.1038/s41598-023-29281-w

Other Link： https://www.nature.com/articles/s41598-023-29281-w

Improved Energy Storage Performance of PVDF Nanocapacitors by Utilizing 2D Inorganic Barrier Layers Reviewed International coauthorship

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

Chemistry Letters Vol. 52 ( 1 ) page： 51 - 54 2023.1

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

Eisuke Yamamoto, Akiko Suzuki, Makoto Kobayashi, Minoru Osada

Nanoscale Vol. 14 ( 32 ) page： 11561 - 11567 2022

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

We found solid-state surfactants as designable crystals suitable for nanostructural control and proposed a novel synthetic route for molecularly-thin Pt metal nanosheets using solid surfactant crystals as a precursor.

DOI： 10.1039/d2nr01807a

Influences of pulverization and annealing treatment on the 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

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

Pulverization followed by annealing treatment improved the activity of BiVO4 although the annealing treatment had a negative impact on the non-milled sample.

DOI： 10.1039/d2se00065b

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

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

Language：English Publishing type：Research paper (scientific journal) Publisher：Ceramic Society of Japan

We present a method for synthesizing brookite-type titanium dioxide (TiO2) using an emulsion-assisted hydrothermal approach and a water-soluble titanium complex with glycolic acid as a complexing agent. In this study, stirred hydrothermal synthesis was used to synthesize water-in-oil emulsions with titanium glycolate complex in the aqueous phase. The resulting brookite-type TiO2 was investigated using Raman spectroscopy for crystal polymorph identification, X-ray Diffraction to identify crystal polymorphs and crystallite size, Transmission Electron Microscope for primary particle size, and crystal shape, and Dynamic Light Scattering for TiO2 secondary particle size in aqueous dispersion. The synthesized brookite-type TiO2 was a needle-like crystal with a width between 20 and 30 nm and a length of more than 70 nm, growing in the b-axis direction at an angle of about 70° from the (120) plane. Furthermore, compared to the conventional synthesis method, the secondary particle size was smaller, and the dispersibility in water was improved. The results show that the brookite-type TiO2 dispersion obtained using the emulsion-assisted hydrothermal method can facilitate the formation of uniform films and can be applied to the electron transport layer of organic perovskite solar cells.

DOI： 10.2109/jcersj2.21127

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

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

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

NaMoO3F and Na5W3O9F5 were synthesized by solvothermal reaction of MoO3 and WO3, respectively, with NaF in nonaqueous solvents. These reactions were realized at low temperatures (150-200 °C) without the use of HF. This synthesis method is much more facile and safe procedure compared with general synthesis methods for oxyfluorides which includes hydrothermal reaction under a presence of HF or solid-state reaction at high temperatures in vacuum sealed tube or under high pressure. In the case of the reaction of MoO3 with NaF, the kind of solvent largely affected the obtained morphologies of NaMoO3F. The morphology in the case of acetonitrile as a solvent was rodlike with a micrometer-scale size, while that in the case of ethanol was polyhedral with a size of several hundred nanometers. In addition, the solvothermal reaction of WO3 with NaF led to the formation of Na5W3O9F5. Also, the difference of solvents for the solvothermal reaction affected the obtained particle sizes. The effect of the solvents on the morphologies of the obtained oxyfluorides probably resulted from the difference of the solubility of NaF and the subsequent dissolution ratio of MoO3 or WO3 in the used solvents. Our synthesis method can expand the applicability of oxyfluorides by providing a new phase and/or unique morphology.

DOI： 10.1021/acs.inorgchem.0c01175

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

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 Open Access

Hiroki Nada, Makoto Kobayashi, Masato Kakihana

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

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

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

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

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

Water-dispersed silicates and water-soluble phosphates, and their use in sol-gel synthesis of silicate- and phosphate-based materials Reviewed

Synthesis of Ba1-xSrxYSi2O5N and Discussion Based on Structure Analysis and DFT Calculation Reviewed International journal Open Access

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 - 271 2019.5

Crystal structures of Ca4+xY3-xSi7O15+xN5-x (0 <= x <= 1) comprising of an isolated [Si7(O,N)19] unit Reviewed International journal Open Access

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

ACTA CRYSTALLOGRAPHICA SECTION E-CRYSTALLOGRAPHIC COMMUNICATIONS Vol. 75 ( Pt 2 ) page： 260 - + 2019.2

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

Hydrothermal Synthesis of Pseudocubic Rutile-Type Titania Particles International journal Open Access

Makoto Kobayashi, Hideki Kato, Takamichi Miyazaki, Masato Kakihana

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

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

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

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

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

Language：English Publishing type：Research paper (scientific journal) Publisher：The Society of Photopolymer Science and Technology(SPST)

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

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

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

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

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

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

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

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

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

Frontiers in Chemistry Vol. 6 page： 467 2018.10

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

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

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

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

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

Makoto Kobayashi, Hideki Kato, Masato Kakihana

Handbook of Sol-Gel Science and Technology: Processing, Characterization and Applications page： 205 - 231 2018.7

Development of Mixed Anion Phosphors Invited Reviewed

Kobayashi Makoto, Kato Hideki, Kakihana Masato

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

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

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

CHEMISTRY LETTERS Vol. 46 ( 10 ) page： 1515 - 1517 2017.10

Language：English Publishing type：Research paper (scientific journal) Publisher：The Chemical Society of 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

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

Makoto Kobayashi, Sungho Lee, Hideki Kato, Masato Kakihana

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

Authorship：Lead author,　Corresponding author 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

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

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

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

Photoluminescence Properties of Double Perovskite Tantalates Activated with Mn4+, AE(2)LaTaO(6):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

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

Development of Crystal Growth Based on Aqueous Solution Processes Invited Reviewed

Makoto Kobayashi

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

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

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

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

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

CHEMISTRY LETTERS Vol. 46 ( 6 ) page： 795 - 797 2017.6

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

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

Site occupancy and luminescence properties of Ca(3)Ln(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

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

Hydrothermal synthesis of brookite-type titania crystals using water-soluble titanium complexes Reviewed

Makoto Kobayashi, Hideki Kato, Masato Kakihana

Titanium Dioxide Nanoparticles: Characterizations, Properties and Syntheses page： 71 - 92 2017.1

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

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

Language：English Publishing type：Research paper (scientific journal) Publisher：The Society of Photopolymer Science and Technology(SPST)

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, α-Ca2Ta2O7 : 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

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

Synthesis and Development of Titania with Controlled Structures Invited Reviewed Open Access

Makoto Kobayashi

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

Screening of Er3+/Yb3+ Codoped RE-Ta-O and RE-Nb-O (RE = Y, La, or Gd) Upconversion Phosphors Reviewed International journal Open Access

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

CHEMISTRY LETTERS Vol. 45 ( 8 ) page： 890 - 891 2016.8

Language：English Publishing type：Research paper (scientific journal) Publisher：The Chemical Society of Japan

Upconversion (UC) phosphors comprising Er3+/Yb3+ codoped 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

Anomalous Orange Light-Emitting (Sr,Ba)2SiO4:Eu(2+) 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

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

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

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

Hiroki Nada, Makoto Kobayashi, Masato Kakihana

JOURNAL OF PHYSICAL CHEMISTRY C Vol. 120 ( 12 ) page： 6502 - 6514 2016.3

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

Effect of Site Occupancies 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

Language：English Publishing type：Research paper (scientific journal) Publisher：The Chemical Society of Japan

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

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

Authorship：Lead author 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

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

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

Kobayashi Makoto, Kato Hideki, Kakihana Masato

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

Authorship：Lead author,　Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japanese Association for Crystal Growth

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

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

Synthesis of titania with controlled structures and its development Reviewed Open Access

小林亮

Journal of the Ceramic Society of Japan Vol. 掲載確定 2016

Graphene/MxWO3 (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

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

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 Open Access

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

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

Photoluminescence Properties of Mn4+-activated Perovskite-type Titanates, La2MTiO6:Mn4+ (M = Mg and Zn) Reviewed International journal Open Access

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

CHEMISTRY LETTERS Vol. 44 ( 11 ) page： 1541 - 1543 2015.11

Language：English Publishing type：Research paper (scientific journal) Publisher：The Chemical Society of 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

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

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

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

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

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

Language：English Publishing type：Research paper (scientific journal) Publisher：The Ceramic Society of Japan

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 353 K 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·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 373 K 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.

DOI： 10.2109/jcersj2.123.751

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

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

Discovery of Novel Delafossite-type Compounds Composed of Copper(I) Lithium Titanium with Photocatalytic Activity for H-2 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

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

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

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

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

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

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

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

DOI： 10.1016/j.jcrysgro.2015.02.056

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

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

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

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

ABSTRACT In this paper, we demonstrated the synthesis of silicate-based phosphors by solution techniques using glycol-modified 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

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

Makoto Kobayashi, Minoru Osada, Hideki Kato, Masato Kakihana

POLYMER JOURNAL Vol. 47 ( 2 ) page： 78 - 83 2015.2

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

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

DOI： 10.1038/pj.2014.89

Crystal structures and luminescence properties of Eu²⁺-activated new NaBa0.5Ca0.5PO₄ and Na₃Ba₂Ca(PO₄)₃. Reviewed International journal

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

Dalton transactions (Cambridge, England : 2003) Vol. 44 ( 4 ) page： 1900 - 4 2015.1

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

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

DOI： 10.1039/c4dt03024a

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

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

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

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

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

DOI： 10.1039/c5ra09149g

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

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

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

Improvement of hydrogen evolution under visible light over Zn1-2x(CuGa)(x)Ga2S4 photocatalysts by synthesis utilizing a polymerizable complex method Reviewed International journal

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

JOURNAL OF MATERIALS CHEMISTRY A Vol. 3 ( 27 ) page： 14239 - 14244 2015

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

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

DOI： 10.1039/c5ta02114f

酸化チタン多形の水熱結晶成長（Crystal Growth of Titania Polymorphs by Hydrothermal Method） Reviewed Open Access

小林亮

結晶成長学会誌 Vol. 42 page： 283 - 289 2015

水に分散可能な無機Siクラスター活用した水溶液プロセスによるケイ酸塩蛍光体の合成 Reviewed Open Access

小林亮, 垣花眞人

粉体および粉末冶金 Vol. 62 page： 127 - 133 2015

A carbon modified NaTaO<inf>3</inf> mesocrystal nanoparticle with excellent efficiency of visible light induced photocatalysis Reviewed International journal

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

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

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

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

DOI： 10.1039/c4ta04132a

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

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

JOURNAL OF LUMINESCENCE Vol. 154 page： 285 - 289 2014.10

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

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

DOI： 10.1016/j.jlumin.2014.05.006

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

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

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

Language：English Publishing type：Research paper (scientific journal) Publisher：The Ceramic Society of Japan

The synthesis of oxyfluoride solid solutions with the composition (Ca1−xSrx)4Si2O7F2 is reported in this study. (Ca1−xSrx)4Si2O7F2 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)4Si2O7F2 solid solutions, except for Sr4Si2O7F2 exhibited photoluminescence under excitation at 300–450 nm 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.

DOI： 10.2109/jcersj2.122.630

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

Minsung Kim, Makoto Kobayashi, Hideki Kato, Masato Kakihana

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

Language：English Publishing type：Research paper (scientific journal) Publisher：The Ceramic Society of Japan

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.

DOI： 10.2109/jcersj2.122.626

Tailoring of deep-red luminescence in Ca2SiO4:Eu(2+). Reviewed International journal

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

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

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

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

DOI： 10.1002/anie.201402520

Photoluminescence properties of dee-red emitting Ca2SiO4 International journal

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

Rare Earths Vol. 64 page： 122 - 123 2014.5

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

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

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

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

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

DOI： 10.1557/jmr.2013.229

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

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

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

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

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

DOI： 10.1016/j.jascer.2014.05.008

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

小林亮

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

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

小林亮, 垣花眞人

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

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

Makoto Kobayashi, Hideki Kato, Masato Kakihana

NANOMATERIALS AND NANOTECHNOLOGY Vol. 3 ( 23 ) page： 1-10 2013.12

A Highly Luminous LiCaPO4:Eu+2 Phosphor Synthesized by a Solution Method Employing a Water-Soluble Phosphate Ester Reviewed International journal Open Access

Minsung Kim, Makoto Kobayashi, Hideki Kato, Masato Kakihana

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

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

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

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

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

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

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

Synthesis of a Novel Bluish-Green Emitting Oxynitride Ca3Al8Si4O17N4:Eu+2 Phosphor in a CaAl4-xSixO7-xNx Solid Soluti Reviewed International journal Open Access

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

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

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

Minoru Osada, Makoto Kobayashi, Masato Kakihana

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

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

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

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

Synthesis of new thiogallate phosphors (Ba1-xSrx)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

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

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

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

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

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

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

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 > 290, > 400, and > 510 nm. Nanoparticles of perovskite-type SrTiO3 were successfully synthesized above pH 12. The photocatalytic activity of SrTiO3 under visible-light (> 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

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

Control of valence band potential and photocatalytic properties of NaxLa1-xTaO1+2xN2-2x 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

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

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

Photocatalytic activities of Cu3xLa1- xTa(7)O(19) solid solutions for H-2 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

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

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

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

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

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

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

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

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

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

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

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

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

Makoto Kobayashi, Hideki Kato, Masato Kakihana

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

Language：English Publishing type：Research paper (scientific journal) Publisher：The Ceramic Society of Japan

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.

DOI： 10.2109/jcersj2.120.494

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

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

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

Synthesis of new thioaluminate phosphors (Ba1-XSrX)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

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

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

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

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

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

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

PubMed

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

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

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

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

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

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

Language：English Publishing type：Research paper (scientific journal) Publisher：Ceramic Society of Japan

Phase- and morphology-control of TiO2 was performed by a facile hydrothermal method using a novel water-soluble titanium–picolinato 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.

DOI： 10.2109/jcersj2.119.513

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

Language：English Publishing type：Research paper (scientific journal) Publisher：The Chemical Society of 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 d0-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

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

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

Masato Kakihana, Makoto Kobayashi, Valery Petrykin, Koji Tomita

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

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

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. The architecture of titanium complexes includes structural motifs of different polymorphic forms of TiO2, 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, TiO2(B) and brookite were prepared in a reproducible and highly selective way. For the first time TiO2(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

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

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

Language：English Publishing type：Research paper (scientific journal) Publisher：The Ceramic Society of Japan

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/dm3, 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.

DOI： 10.2109/jcersj2.117.320

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

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

Language：English Publishing type：Research paper (scientific journal) Publisher：The Ceramic Society of Japan

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 ([Ti4(C2H2O3)4(C 2H3O3)2(O2)4O2]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.

DOI： 10.2109/jcersj2.117.347

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

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

Makoto Kobayashi, Valery Petrykin, Masato Kakihana, Koji Tomita

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

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

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

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

Synthesis of TiO_2 (B) using glycolato titanium complex and post-synthetic hydrothermal crystal growth of TiO_2 (B) Reviewed

冨田恒之, 小林亮, ペトリキンヴァレリー, 垣花眞人

Journal of Crystal Growth 311 page： 619 - 622 2009

Hydrothermal Synthesis and Photocatalytic Activity of Whisker-like Rutile-type Titanium Dioxide Reviewed Open Access

小林亮

Journal of the American Ceramic Society 92 2009

チタン錯体水溶液からの酸化チタン光触媒の合成 Reviewed

小林亮, 冨田恒之

化学工業 60 page： 71 - 77 2009

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

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

Masato Kakihana, Makoto Kobayashi, Valery Petrykin, Koji Tomita

Acta Crystallographica Section A ( 64 ) page： C20 2008.8

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

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

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

Makoto Kobayashi, Valery Petrykin, Koji Tomita, Masato Kakihana

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN Vol. 116 ( 1352 ) page： 578 - 583 2008.4

Language：English Publishing type：Research paper (scientific journal) Publisher：The Ceramic Society of Japan

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 m2/g. The powder composed of anatase and brookite synthesized by hydrothermal treatment of the titanium-threonine complex aqueous solution at 200°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 m2/g).

DOI： 10.2109/jcersj2.116.578

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

Language：English Publishing type：Research paper (international conference proceedings)

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

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

Selective synthesis of nano-crystalline TiO_2 polymorphs from new water-soluble titanium complexes Reviewed Open Access

小林亮

Acta Crystallographica Section A 64 2008

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

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

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

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

Makoto Kobayashi, Valery Petrykin, Masato Kakihana, Koji Tomita

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

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

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

Kobayashi, Makoto, Petrykin, Valery V., Kakihana, Masato

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

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

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

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 ed. in English) Vol. 45 ( 15 ) page： 2378 - 81 2006.4

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

The Owakidani Tephra Group : A Newly Discovered Post-magmatic Eruption Product of Hakone Volcano, Japan Reviewed Open Access

KOBAYASHI Makoto, MANNEN Kazutaka, OKUNO Mitsuru, NAKAMURA Toshio, HAKAMATA Kazuo

BULLETIN OF THE VOLCANOLOGICAL SOCIETY OF JAPAN Vol. 51 ( 4 ) page： 245 - 256 2006

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Volcanological Society of Japan

We discovered a set of phreatic explosion deposits, herein referred to as the Owakidani tephra group, on the northern slope of Mt. Kamiyama and in the Owakidani fumarolic area of the Hakone Volcano. The tephra group is the product of the volcanic activities since the latest magmatic eruption of Hakone Volcano at around 2.9ka. It comprises five units named Hk-Ow1 to Hk-Ow5 in the ascending order. Both Hk-Ow1 and Hk-Ow2 comprise tephra fall deposits and secondary debris flow deposits. In addition to these deposits, Hk-Ow2 is also associated with surge deposits. Hk-Ow3, Hk-Ow4 and Hk-Ow5 consist of tephra fall deposits. The ash of these tephra fall deposits and the matrix of the secondary debris flows are principally composed of clay, altered lithics and secondary minerals supposed to be of fumarolic area origin. It is possible that Hk-Ow1 and Hk-Ow2 erupted from a fissure on the northeastern ridge of Mt. Kamiyama, while Hk-Ow3, Hk-Ow4 and Hk-Ow5 erupted at Owakidani. No juvenile material was found within the deposits of these eruptions except for Hk-Ow2, while the surge deposit of Hk-Ow2 contained trace amounts of volcanic glass fragment. Although it is considered that the principal nature of the eruptions of the Owakidani tephra group is phreatic, the deformation of the edifice around the source area implies the possibility of magma intrusion to shallow levels. Based on the calendar ages of the Owakidani tephra group and the stratigraphic position of the Kozushima-Tenjosan tephra, we estimated that Hk-Ow3, Hk-Ow4 and Hk-Ow5 erupted in relatively short intervals between the latter half of the 12th and 13th centuries. On the other hand, Hk-Ow1 and Hk-Ow2 erupted at around 3 kyr BP and 2kyr BP, respectively. The eruption ages of the Owakidani tephra group generally correspond to the seismic events that occurred in the Kozu-Matsuda Faults and the Tanna-Hirayama tectonic line. It is suggested that the activity of the Hakone Volcano may be closely related to the tectonic events in this region.

DOI： 10.18940/kazan.51.4_245