Faculty Profiles - KOBAYASHI Makoto

Papers - KOBAYASHI Makoto

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

Hiroki Nada, Makoto Kobayashi, Masato Kakihana

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

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

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

DOI： 10.1021/acsomega.9b01100

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

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

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

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

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

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

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

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

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

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

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

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

DOI： 10.1107/S2056989019001257

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Hydrothermal Synthesis of Pseudocubic Rutile-Type Titania Particles International journal

Makoto Kobayashi, Hideki Kato, Takamichi Miyazaki, Masato Kakihana

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

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

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

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

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

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

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

DOI： 10.2494/photopolymer.32.593

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

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

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

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

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

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

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

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

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

Frontiers in Chemistry Vol. 6 page： 467 2018.10

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

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

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

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

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：CHEMICAL SOC JAPAN

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

DOI： 10.1246/cl.170652

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

Makoto Kobayashi, Sungho Lee, Hideki Kato, Masato Kakihana

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

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

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

DOI： 10.1016/j.jascer.2017.06.006

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

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

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

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

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

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

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

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

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

DOI： 10.1021/acs.jpcc.7b06280

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Development of Crystal Growth Based on Aqueous Solution Processes Invited Reviewed

Makoto Kobayashi

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

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

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Papers - KOBAYASHI Makoto