Faculty Profiles - TOKUNAGA, Tomoharu

Papers - TOKUNAGA, Tomoharu

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Small Nanosized Oxygen-Deficient Tungsten Oxide Particles: Mechanistic Investigation with Controlled Plasma Generation in Water for Their Preparation Reviewed International journal

Yohei Ishida, Shingo Motono, Wataru Doshin, Tomoharu Tokunaga, Hiroki Tsukamoto, Tetsu Yonezawa

ACS OMEGA Vol. 2 ( 8 ) page： 5104 - 5110 2017.8

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

Production of oxygen-deficient tungsten oxide nanoparticles with a diameter of around 10 nm have been successfully developed using a microwave-induced plasma in liquid technique. The prepared blue-green nanoparticles exhibit strong absorption in the visible region; thus, these could be efficient visible-light photocatalysts. The high-angle annular dark-field images revealed the dislocation of tungsten, which causes oxygen deficiencies.

DOI： 10.1021/acsomega.7b00986

Web of Science

Scopus

PubMed

Nanophase-separated Ni3Nb as an automobile exhaust catalyst International journal

Toyokazu Tanabe, Tsubasa Imai, Tomoharu Tokunaga, Shigeo Arai, Yuta Yamamoto, Shigenori Ueda, Gubbala V. Ramesh, Satoshi Nagao, Hirohito Hirata, Shin-ichi Matsumoto, Takeshi Fujita, Hideki Abe

CHEMICAL SCIENCE Vol. 8 ( 5 ) page： 3374 - 3378 2017.5

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

Catalytic remediation of automobile exhaust has relied on precious metals (PMs) including platinum (Pt). Herein, we report that an intermetallic phase of Ni and niobium (Nb) (i.e., Ni3Nb) exhibits a significantly higher activity than that of Pt for the remediation of the most toxic gas in exhaust (i.e., nitrogen monoxide (NO)) in the presence of carbon monoxide (CO). When subjected to the exhaust-remediation atmosphere, Ni3Nb spontaneously evolves into a catalytically active nanophase-separated structure consisting of filamentous Ni networks (thickness < 10 nm) that are incorporated in a niobium oxide matrix (i.e., NbOx (x < 5/2)). The exposure of the filamentous Ni promotes NO dissociation, CO oxidation and N-2 generation, and the NbOx matrix absorbs excessive nitrogen adatoms to retain the active Ni-0 sites at the metal/oxide interface. Furthermore, the NbOx matrix immobilizes the filamentous Ni at elevated temperatures to produce long-term and stable catalytic performance over hundreds of hours.

DOI： 10.1039/c6sc05473k

Web of Science

Scopus

PubMed

Methane decomposition for hydrogen production by catalytic activity of carbon black under low flow rate conditions

Tomoharu Tokunaga, Naoyuki Kishi, Kenya Yamakawa, Katsuhiro Sasaki, Takahisa Yamamoto

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN Vol. 125 ( 4 ) page： 185 - 189 2017.4

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

Recently, carbon materials were reported to work as catalysts for the production of H-2 from hydrocarbons. However, the hydrogen production rate is extremely low. To broaden the scope of carbon materials as catalysts for the decomposition of hydrocarbons, a higher H-2 production rate is required. Thus, the hydrogen production rate under conditions employing a low flow rate of hydrocarbon per unit area and a large quantity of carbon materials as the catalyst should be evaluated, and the influence of these conditions on the rate of H-2 production by carbon materials should be discussed. Herein, the H-2 production rate was measured under conditions employing a low flow rate of CH4 and a large quantity of carbon black (CB) as a catalyst. H-2 production started at 600 degrees C and the production rate was less than 0.1%. The transmission electron microscope image of CB heated in CH4 atmosphere demonstrated that a low flow rate of CH4 does not affect the reaction site (i.e., graphite edges) of CB. However, the H-2 production rate was extremely low compared to that achieved with a high flow rate. It is proposed that there is an optimal flow rate for maintaining the catalytic activity at the graphite edge of CB for decomposition of CH4. (C) 2017 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.16246

Web of Science

Scopus

Preparation of Au/Pd Bimetallic Nanoparticles by a Microwave-Induced Plasma in Liquid Process

Hiroaki Shirai, Mai Thanh Nguyen, David Cempel, Hiroki Tsukamoto, Tomoharu Tokunaga, Ying-Chih Liao, Tetsu Yonezawa

BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN Vol. 90 ( 3 ) page： 279 - 285 2017.3

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

Au/Pd alloy nanoparticles (NPs) were successfully synthesized using HAuCl4, H2PdCl4, and alpha-thioglycerol as precursors and a stabilizer, respectively, by microwave-induced plasma in liquid process (MWPLP). After only several minutes of microwave irradiation, metallic NPs were obtained in aqueous environment without any reducing agent. The reduction mechanism of metal ions was confirmed by UV-vis spectral changes. The results from HAADF-STEM and EDS indicated that synthesized NPs were bimetallic Au/Pd. Moreover, XRD patterns of synthesized NPs implied that the composition of bimetallic NPs could be controlled by changing the initial ratio of metal precursors.

DOI： 10.1246/bcsj.20160333

Web of Science

Scopus

Directly determining the polarity of WC grains in WC-12 wt%Co alloy by ABF-STEM Reviewed

Yoshimitsu Hayashi, Tomoharu Tokunaga, Katsuhiro Sasaki, Takahisa Yamamoto

INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS Vol. 62 page： 9 - 13 2017.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

WC grains in WC-Co alloys are shaped as truncated triangular prisms, each with a basal plane of a (0001) truncated triangle and two {1 (1) over bar 00} prismatic planes, one narrower and one wider. This anisotropic shape is related to the polarity of the WC lattice, which comes from the difference in the spacing of the W and C layers in the <0001> projection. We directly determined the relationship between the two {1 (1) over bar 00} prismatic planes and the polarity of the WC lattice by using high-resolution scanning transmission electron microscopy (STEM). High-angle annular dark-field STEM and annular bright-field STEM revealed that the wider prismatic plane had W and C atomic layers with a shorter spacing, while the narrower plane had a longer spacing. The WC/Co interface on the wider prismatic side was atomically flat, while many steps formed on the surface of the narrower prismatic side. This difference in step formation at these interfaces could have come from the difference in how their W-C bonds formed. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijrmhm.2016.10.013

Web of Science

Scopus

Methane Decomposition for Hydrogen Production by Catalytic Activity of Carbon Black under Low Flow Rate Conditions

Tomoharu Tokunaga, Naoyuki Kishi, Kenya Yamakawa, Katsuhiro Sasaki, Takahisa Yamamoto

ACS-Japan Vol. 125 ( 4 ) page： 185-189 2017

Water transport phenomena through membranes consisting of vertically-aligned double-walled carbon nanotube array

Hidetoshi Matsumoto, Shuji Tsuruoka, Yasuhiko Hayashi, Koji Abe, Kenjiro Hata, Shaoling Zhang, Yoshitaka Saito, Motohiro Aiba, Tomoharu Tokunaga, Toru Iijima, Takuma Hayashi

Carbon Vol. 120 page： 358–365 2017

Nanophase-separated Ni3Nb as Automobile Exhaust Catalysts Reviewed

Toyokazu Tanabe, Tsubasa Imai, Tomoharu Tokunaga, Shigeo Arai, Yuta Yamamoto, Shigenori Ueda, Gubbala V. Ramesh, Satoshi Nagao, Hirohito Hirata, Shin-ichi, Matsumoto, Takeshi Fujita, Hideki Abe

Chemical Science Vol. 8 page： 3374-3378 2017

Preparation of Au/Pd bimetallic nanoparticles by a microwave-induced plasma in liquid process Reviewed

Hiroaki Shirai, Mai Thanh Nguyen, David Čempel, Hiroki Tsukamoto, Tomoharu Tokunaga, Ying-Chih Liao, and Tetsu Yonezawa

Bulletin of the Chemical Society of Japan Vol. 90 ( 3 ) page： 279-285 2017

Intentionally Encapsulated Metal Alloys within Vertically Aligned Multi-Walled Carbon Nanotube Array via Chemical Vapor Deposition Technique

Hayashi Yasuhiko, Inoue Hirotaka, Hayashi Takuma, Hada Masaki, Nishikawa Takeshi, Tokunaga Tomoharu, Amaratunga G. A. J.

2017 IEEE INTERNATIONAL CONFERENCE ON MANIPULATION, MANUFACTURING AND MEASUREMENT ON THE NANOSCALE (3M-NANO) page： 357-361 2017

Intentionally Encapsulated Metal Alloys within Vertically Aligned Multi-Walled Carbon Nanotube Array via Chemical Vapor Deposition Technique Reviewed

Yasuhiko Hayashi, Hirotaka Inoue, Takuma Hayashi, Masaki Hada, Takeshi Nishikawa, Tomoharu Tokunaga, G. A. J. Amaratunga

2017 IEEE INTERNATIONAL CONFERENCE ON MANIPULATION, MANUFACTURING AND MEASUREMENT ON THE NANOSCALE (3M-NANO) page： 357 - 361 2017

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

This paper presents a growth and characterization of vertically aligned PdxCo1-x alloy encapsulated inside Multi-Walled Carbon Nanotube (MWCNT) arrays on Pd/Co thin layers coated on Si substrate by a dc bias-enhanced plasma chemical vapor deposition (CVD) method. The Metal Alloy Encapsulated within MWCNTs (MAE-MWCNTs) were characterized by a scanning electron microscope (SEM) and a transmission electron microscopy (TEM). The SEM images show the teardrop-shape particles encapsulated within the tube top of MWCNTs. A vibrating sample magnetometer was used to study the magnetism of a large number of MAE-MWCNTs on Si substrate at room temperature. The hysteresis loop of the ME-MWCNTs shows clear ferromagnetic behavior and the easy axis of magnetization is parallel to the MEA-MWCNT tube axis, as can be elucidated from the large coercive fields and remanence values. Moreover, TEM off-axis electron holograms were used to study the magnetism of the individual MAE-MWCNT or the two pair of MAE-MWCNTs. Based on electron holography, we have successfully obtained the saturation magnetization of 0.7 T and 1.12 T for the individual MAE-MWCNT with diameters of 41 nm and 83 nm, respectively.

Web of Science

Double target sputtering into liquid Reviewed

Mai Thanh Nguyen, Tetsu Yonezawa, Yuan Wang, Tomoharu Tokunaga

Materials Letters Vol. 171 ( 15 ) page： 75-78 2016

Earth-Abundant and Durable Nanoporous Catalyst for Exhaust-Gas Conversion Reviewed

Takeshi Fujita,Hideki Abe,Toyokazu Tanabe,Yoshikazu Ito,Tomoharu Tokunaga,Shigeo Arai,Yuta Yamamoto,Akihiko Hirata,Mingwei Chen

Advanced Functional Materials page： 1-8 2016

Hard-Templating Synthesis of Macroporous Platinum Microballs Reviewed

Hiroaki Shirai, Yu-Yuan Huang, Tetsu Yonezawa,* Wei-Chen Chang, Tomoharu Tokunaga, Saad Alshehri, Bo Jiang, Yusuke Yamauchi, and Kevin C.-W. Wu

Materials Letters Vol. 164 ( 1 ) page： 488-492 2016

Synthesis of zirconium oxynitride in air under DC electric fields Reviewed

Nobuhiro Morisaki, Hidehiro Yoshida, Koji Matsui, Tomoharu Tokunaga, Katsuhiro Sasaki, Takahisa Yamamoto

Applied Physics Letter Vol. 109 page： 083104(1)- 083104(4) 2016

Formation of grain boundary second phase in BaTiO3 polycrystal under a high DC electric field at elevated temperatures Reviewed

Hidehiro YOSHIDA, Akinori UEHASHI, Tomoharu TOKUNAGA, Katsuhiro SASAKI, Takahisa YAMAMOTO

Journal of the Ceramic Society of Japan Vol. 124 ( 4 ) page： 388-392 2016

Matrix Sputtering into Liquid Mercaptan: From Blue-Emitting Copper Nanoclusters to Red-Emitting Copper Sulfide Nanoclusters Reviewed

Matteo Porta, Mai Thanh Nguyen, Tomoharu Tokunaga, Yohei Ishida, Wei-Ren Liu, Tetsu Yonezawa

Langmuir Vol. 32 page： 12159-12165 2016

Matrix Sputtering into Liquid Mercaptan: From Blue-Emitting Copper Nanoclusters to Red-Emitting Copper Sulfide Nanoclusters Reviewed

Matteo Porta, Mai Thanh Nguyen, Tomoharu Tokunaga, Yohei Ishida, Wei-Ren Liu, Tetsu Yonezawa

Langmuir Vol. 32 page： 12159-12165 2016

Plasma-Induced Tungsten Doping of TiO2 Nanoparticles for Enhanced Photocatalysis using Visible Light Reviewed

Vol. 17 ( 38 ) page： 24556-24559 2015

Hard-Templating Synthesis of Macroporous Platinum Microballs (MPtM) Reviewed

Hiroaki Shirai, Yu-Yuan Huang, Tetsu Yonezawa,* Wei-Chen Chang, Tomoharu Tokunaga, Saad Alshehri, Bo Jiang, Yusuke Yamauchi, and Kevin C.-W. Wu

Materials Letters Vol. 164 ( 1 ) page： 488-492 2015

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Papers - TOKUNAGA, Tomoharu