研究者詳細 - 大久保　貴広

論文 - 大久保　貴広

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Green synthesis of mesoporous hematite (alpha-Fe2O3) nanoparticles and their photocatalytic activity 査読

Bashir Ahmmad, Kwati Leonard, Md Shariful Islam, Junichi Kurawaki, Manickavachagam Muruganandham, Takahiro Ohkubo, Yasushige Kuroda

ADVANCED POWDER TECHNOLOGY 24 ( 1 ) 160 - 167 2013年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

A green synthesis method for the preparation of mesoporous alpha-Fe2O3 nanoparticles has been developed using the extract of green tea (camellia sinensis) leaves. This simple and one-step method can suitably be scaled up for large-scale synthesis. The as-prepared mesoporous nanoparticles were characterized by SEM, TEM, XRD, XPS, Raman, UV-visible spectroscopy and N-2 adsorption analysis. The nanoparticles were highly pure and well crystallized with an average particle size of 60 nm. The photocatalytic activity of nanoparticles was evaluated by the amount of hydroxyl radical formation under visible light irradiation detected by fluorescence spectroscopy. The as-prepared alpha-Fe2O3 showed two times higher activity than commercial alpha-Fe2O3 in term of hydroxyl radical formation and enhanced performance in a photoelectrochemical cell. Also, a plausible mechanism for the formation of mesoporous alpha-Fe2O3 has been suggested. (C) 2012 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

DOI： 10.1016/j.apt.2012.04.005

TiO2/TaON- and TiO2/BiOI-based solid-state solar cells 査読

Bashir Ahmmad, Junichi Kurawaki, Takahiro Ohkubo, Fumihiko Hirose

Journal of Energy Engineering 139 ( 4 ) 338 - 342 2013年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：American Society of Civil Engineers (ASCE)

A three-phase solid-state solar cell (SSSC) has been developed successfully using TaON nanoparticles or BiOI microspheres as a sensitizer material over a TiO2 film and CuI as a hole collector. Stable current (I sc)-voltage (Voc) curves are found under ultraviolet UV visible light irradiation with an efficiency of 0.15% and 0.10% for TaON- and BiOI-based solar cells, respectively. The observed photocurrents in SSSCs are approximately 10 and 48 times higher than those in wet-type solar cells (WSCs) based on TaON and BiOI, respectively. A plausible mechanism of charge transfer and hole filling is discussed in terms of the band gap energy and band position of the semiconductor materials. © 2013 American Society of Civil Engineers.

DOI： 10.1061/(ASCE)EY.1943-7897.0000130

Photosensitized hydrogen evolution from water using single-walled carbon nanotube/fullerodendron/Pt(II) coaxial nanohybrids 査読

Yukari Sasada, Tomoyuki Tajima, Takaaki Wada, Tetsuya Uchida, Masayasu Nishi, Takahiro Ohkubo, Yutaka Takaguchi

NEW JOURNAL OF CHEMISTRY 37 ( 12 ) 4214 - 4219 2013年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ROYAL SOC CHEMISTRY

Direct incorporation of a Pt(II) complex into the shell of SWCNT/fullerodendron coaxial nanohybrids produces a new coaxial nanowire, SWCNT/fullerodendron/Pt(II), that shows efficient photocatalytic activity for hydrogen evolution from water (Phi = 0.16 upon irradiation at 450 +/- 5 nm) without any aid of electron relay such as methyl viologen.

DOI： 10.1039/c3nj00790a

Template-free fabrication of a cylindrical macropore array in SnO2 査読

Yushi Ozawa, Tomoyuki Tajima, Masayasu Nishi, Takahiro Ohkubo, Yutaka Takaguchi

RSC ADVANCES 3 ( 45 ) 22949 - 22952 2013年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ROYAL SOC CHEMISTRY

A simple sol-gel condensation of tin(IV) tert-butoxide led to the formation of meso/macroporous membranes. SEM observation clearly shows the cylindrical macropore array, of which mean pore diameter is controllable between 200 and 800 nm. The existence of slit-shaped mesopores (12 nm) was confirmed by a N-2 adsorption-desorption experiment.

DOI： 10.1039/c3ra43642j

Structure of hydrated cobalt ions confined in the nanospace of single-walled carbon nanotubes 査読

Bashir Ahmmad, Masayasu Nishi, Fumihiko Hirose, Takahiro Ohkubo, Yasushige Kuroda

PHYSICAL CHEMISTRY CHEMICAL PHYSICS 15 ( 21 ) 8264 - 8270 2013年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ROYAL SOC CHEMISTRY

The structure of hydrated Co ions confined in the nanospace of single-walled carbon nanotubes (SWNTs) has been studied using the X-ray absorption fine structure (XAFS) technique. Water adsorption isotherms on Co-impregnated SWNTs indicate a high affinity of Co ions to water molecules. The results of XAFS analysis provided the information on the proportion of dissolved species in nanospaces against the total amount of cobalt ions adsorbed on the open-pored SWNT. The structural information of the first shell around a Co ion was expressed in terms of the hydration number, Co-O distance and Debye-Waller factor. The actual coordination number and the interatomic distance of Co-O for the dissolved species were remarkably reduced compared to the bulk aqueous solution indicating the dehydration of water molecules from Co ions and a compact hydrated structure in the micropore of SWNTs.

DOI： 10.1039/c3cp50181g

Arrangement and Dispersion of Rh and Pt Atoms on Graphene Oxide Sheets 査読

Kazuma Gotoh, Hideki Hashimoto, Ryo Kawai, Yuta Nishina, Eiji Fujii, Takahiro Ohkubo, Atsushi Itadani, Yasushige Kuroda, Hiroyuki Ishida

CHEMISTRY LETTERS 41 ( 7 ) 680 - 682 2012年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：CHEMICAL SOC JAPAN

Hybrid materials of ultimately minimized metal particles, namely, isolated atoms or subnano-sized particles, on thermally exfoliated graphene oxide sheets were produced using cation-exchanged highly oxidized graphite as a precursor. Rh atoms on graphene sheets arrange with a regular spacing of 0.50 or 0.45 nm and form square or rectangular grid patterns, whereas isolated Pt atoms disperse on graphene sheets randomly.

DOI： 10.1246/cl.2012.680

Dual-Copper Catalytic Site Formed in CuMFI Zeolite Makes Effective Activation of Ethane Possible Even at Room Temperature 査読

Atsushi Itadani, Hiroe Torigoe, Takashi Yumura, Takahiro Ohkubo, Hisayoshi Kobayashi, Yasushige Kuroda

JOURNAL OF PHYSICAL CHEMISTRY C 116 ( 19 ) 10680 - 10691 2012年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER CHEMICAL SOC

The role of dual-cation sites in zeolites has received a renaissance in chemistry and industry directed toward fixation and activation of various gases; such sites may be expected to be more efficient than a single-cation site. We aimed to clarify the real active centers in the copper-ion-exchanged MFI-type zeolite (CuMFI) for ethane (C2H6). A peculiar feature was found in the appearance of the characteristic IR bands at 2644 and 2582 cm(-1) when C2H6 was adsorbed on Cu+ formed in CuMFI. The existence of dual species composed of two Cu+ ions bridging C2H6 was clearly indicated by extended X-ray absorption fine structure (EXAFS) data. Density functional theory calculations gave clear evidence that the two IR bands are distinctly due to C2H6 adsorbed on the dual-Cu+ site and not on a single site; this agrees with the EXAFS data. These data lead us to conclude that the dual-Cu+ site in the CuMFI sample is indispensable for efficient activation of C2H6 through the simultaneous interaction of C2H6 with two Cu+ ions.

DOI： 10.1021/jp3022858

Water-initiated ordering around a copper ion of copper acetate confined in slit-shaped carbon micropores 査読

Takahiro Ohkubo, Yutaro Takehara, Yasushige Kuroda

MICROPOROUS AND MESOPOROUS MATERIALS 154 82 - 86 2012年5月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Physical or chemical properties of hydrated ions confined in solid nanospaces are not substantially understood, although they are indispensable for the development of new science and technology. We study the local structure around a Cu2+ of copper acetate restricted in slit-shaped micropore of two kinds of activated carbon fibers (ACFs) by X-ray absorption fine structure (XAFS) technique. The results indicate that the highly dispersed copper acetate on the surface of ACFs can be partially dissolved after the adsorption of water. Also, when we adsorb water to copper acetate-deposited ACFs, the Cu-Cu distance of the dinuclear species of copper acetate becomes longer with the ordering of the Cu-Cu bond because of the reduction of the number of the bridging carboxylate inside the micropore. In addition, the results of EXAFS spectra suggest that water molecules can play an important role for the ordering of the specific dinuclear complex of copper acetate formed in the micropore even though the number of bridging carboxylate which can stabilize the dinuclear structure is decreased by the adsorption of water. (C) 2011 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.micromeso.2011.09.011

Unprecedented Reversible Redox Process in the ZnMFI-H-2 System Involving Formation of Stable Atomic Zn-0 査読

Akira Oda, Hiroe Torigoe, Atsushi Itadani, Takahiro Ohkubo, Takashi Yumura, Hisayoshi Kobayashi, Yasushige Kuroda

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 51 ( 31 ) 7719 - 7723 2012年

Visible-Light-Derived Photocatalyst Based on TiO2-delta N delta with a Tubular Structure 査読

Yoshikazu Hirose, Toshinori Mori, Yuka Morishita, Atsushi Itadani, Takayuki Kudoh, Takahiro Ohkubo, Tomoko Matsuda, Shigeharu Kittaka, Yasushige Kuroda

INORGANIC CHEMISTRY 50 ( 20 ) 9948 - 9957 2011年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER CHEMICAL SOC

We succeeded in achieving visible-light responsiveness on a tubular TiO2 sample through the treatment of a tubular TiO2 that has a large surface area with an aqueous solution of ammonia or triethylamine at room temperature and subsequent calcination at 623 K, which produced a nitrided tubular TiO2 sample. It was found that the ease of nitridation is dependent on the surface states; washing the tubular TiO2 sample with an aqueous acidic solution is very effective and indispensable. This treatment causes the appearance of acidic sites on the tubular TiO2, which was proved by the following experiments: NH3 temperature-programmed desorption and two types of organic reactions exploiting the acid properties. The prepared samples, TiO2-delta N delta, efficiently absorb light in the visible region, and they exhibit a prominent feature for the decomposition of methylene blue in an aqueous solution at 300 K under irradiation with visible light, indicating the achievement of visible-light responsiveness on the tubular TiO2 sample. This type of tubular TiO2-delta N delta sample has merit in the sense that it has a large surface area and a characteristic high transparency for enabling photocatalytic reactions because it has a tubular structure and is composed of thin walls.

DOI： 10.1021/ic200424v

Actual Structure of Dissolved Zinc Ion Restricted in Less Than 1 Nanometer Micropores of Carbon 査読

Takahiro Ohkubo, Masayasu Nishi, Yasushige Kuroda

JOURNAL OF PHYSICAL CHEMISTRY C 115 ( 30 ) 14954 - 14959 2011年8月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER CHEMICAL SOC

The structures and properties of hydrated ions confined in solid nanospaces are not substantially understood, although they are indispensable for the development of new devices such as electrical double-layer capacitors. We describe the hydration structure around a Zn2+ restricted in slit-shaped micropores of two kinds of activated carbon fibers (ACF) by the analysis of X-ray absorption fine structure (XAFS) spectra. The proportion of dissolved species against the total adsorbed amounts of Zn2+ on ACF was decreased with the reduction of the average micropore width of ACF. We could trace the actual structure of "nanosolution" around a Zn2+ restricted in less than 1 nm pore by extended XAFS (EXAFS) spectra with applying these values. Our results strongly indicate that the dehydrated structure can be stably formed inside the micropore whose pore size is less than the total diameter of the symmetrically hydrated ion, where the dehydrated ions can be stabilized by the strong potential well of the micropore.

DOI： 10.1021/jp2043653

Exfoliated graphene sheets decorated with metal/metal oxide nanoparticles: Simple preparation from cation exchanged graphite oxide 査読

Kazuma Gotoh, Taro Kinumoto, Eiji Fujii, Aki Yamamoto, Hideki Hashimoto, Takahiro Ohkubo, Atsushi Itadani, Yasushige Kuroda, Hiroyuki Ishida

CARBON 49 ( 4 ) 1118 - 1125 2011年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

We produced carbon hybrid materials of graphene sheets decorated with metal or metal oxide nanoparticles of gold, silver, copper, cobalt, or nickel from cation exchanged graphite oxide. Measurements using powder X-ray diffraction, transmission electron microscopy, and X-ray absorption spectra revealed that the Au and Ag in the materials (Au-Gr and Ag-Gr) existed on graphene sheets as metal nanoparticles, whereas Cu and Co in the materials (Cu-Gr and Co-Gr) existed as a metal oxide. Most Ni particles in Ni-Gr were metal, but the surfaces of large particles were partly oxidized, producing a core-shell structure. The Ag-Gr sample showed a catalytic activity for the oxygen reduction reaction in 1.0 M KOH aq. under an oxygen atmosphere. Ag-Gr is superior as a cathode in alkaline fuel cells, which should not be disturbed by the methanol cross-over problem from the anode. We established an effective approach to prepare a series of graphene-nanoparticle composite materials using heat treatment. (C) 2010 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.carbon.2010.11.017

Template-Free Synthesis of Self-Assembled Co3O4 Micro/Nanocrystals 査読

R. Amutha, S. Akilandeswari, M. Muruganandham, Mika Sillanpaa, Bashir Ahmmad, Takahiro Ohkubo

JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 11 ( 4 ) 3171 - 3179 2011年4月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER SCIENTIFIC PUBLISHERS

In this article, we have reported the fabrication of various morphological porous Co3O4 by thermal decomposition of cobalt oxalate at open atmospheric conditions. Uniform cobalt oxalate microrods and microneedles were synthesized without using any surfactants or templates in large scale. The cobalt oxalate preparation method was played a crucial role on the crystal structure and its morphology. The as prepared cobalt oxalates and its corresponding cobalt oxides were characterized by using the thermogravimetric analysis, X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM) and nitrogen adsorption analysis. The XRD results indicated that the orthorhombic and monoclinic cobalt oxalates were formed in different experimental conditions. The influence of preparation method of cobalt oxalates and cobalt precursors on the final morphology has been investigated. The M-H loop of the Co3O4 porous microrods and microneedles showed the presence of paramagnetic properties at room temperatures. A plausible mechanism of both cobalt oxalates and Co3O4 formation was proposed based on the experimental results.

DOI： 10.1166/jnn.2011.3848

Structural optimization of arranged carbon nanotubes for hydrogen storage by grand canonical Monte Carlo simulation 査読

Daiki Minami, Takahiro Ohkubo, Yasushige Kuroda, Kenichi Sakai, Hideki Sakai, Masahiko Abe

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 35 ( 22 ) 12398 - 12404 2010年11月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

We revealed the arrangement of single wall carbon nanotube (SWNT) which is suitable for the adsorption of hydrogen by means of grand canonical Monte Carlo (GCMC) simulation with simple cylindrical model Here, we calculated the amount of adsorbed hydrogen with triangular lattice (TL) and square lattice (SL) model for the bundle structure with venous kinds of tube diameters (D) and inter axis distances (R(a)) Our results indicate that any arrangements having smaller R(a) are not suitable for the storage of hydrogen and the adsorption amount of hydrogen can be achieved the target value (6 wt % and 45 kg m(-3)) proposed by Department of Energy (DOE) in United States by SWNTs having larger R(a) at 77 K and 1 MPa Furthermore these results show that the best arrangement of SWNTs for the adsorption of hydrogen at this condition is TL structure having R(a) = 2 159 nm and D = 1 227 nm (C) 2010 Professor T Nejat Veziroglu Published by Elsevier Ltd All rights reserved

DOI： 10.1016/j.ijhydene.2010.08.082

Direct Information on Structure and Energetic Features of Cu+-Xe Species Formed in MFI-Type Zeolite at Room Temperature 査読

Hiroe Torigoe, Toshinori Mori, Kazuhiko Fujie, Takahiro Ohkubo, Atsushi Itadani, Kazuma Gotoh, Hiroyuki Ishida, Hiroki Yamashita, Takashi Yumura, Hisayoshi Kobayashi, Yasushige Kuroda

JOURNAL OF PHYSICAL CHEMISTRY LETTERS 1 ( 18 ) 2642 - 2650 2010年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER CHEMICAL SOC

The interacted species of Xe with metal ions that are stable at room temperature are not known and are a subject of interest for fundamental chemistry We have,experimentally found a new and stable Xe species, XeCu+, which was formed it room temperature in a copper ion exchanged MFI-type zeolite. The presence of a prominent interaction between Cu+ in MFI and Xe, which has a covalent nature, was for the first time evidenced from experimental in situ synchrotron X-ray absorption fine structure and heat of adsorption measurements; the Cu+-Xe bond length of 2.45 angstrom and the bonding energy of ca. 60 kJ mol(-1). The bonding nature between Xe and Cu+ in the MFI zeolite was discussed utilizing density functional theory; the observed significant stabilization comes from the d(Cu+ in MFI)-p(Xe) orbital interaction. These new findings may pave a new way to developing fundamental chemistry of Xe compounds.

DOI： 10.1021/jz100838c

その他リンク： http://orcid.org/0000-0001-5907-3683

Existence of dual species composed of Cu+ in CuMFI being bridged by C2H2 査読

Atsushi Itadani, Takashi Yumura, Takahiro Ohkubo, Hisayoshi Kobayashi, Yasushige Kuroda

PHYSICAL CHEMISTRY CHEMICAL PHYSICS 12 ( 24 ) 6455 - 6465 2010年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ROYAL SOC CHEMISTRY

The interaction of ethyne (C2H2), as well as of carbon dioxide (CO2), with copper-ion-exchanged MFI zeolite (CuMFI) at room temperature was examined. It was found that CuMFI preferentially adsorbs C2H2, while this material does not respond to CO2. To clarify the specificity of CuMFI, a combination of various experimental techniques and theoretical calculations was adopted. Distinctive interaction energies of 140 and 110 kJ mol(-1) were clearly observed at the initial stage of C2H2 adsorption on CuMFI, suggesting the presence of two types of adsorbed C2H2. Two distinct IR bands at 1620 and 1814 cm(-1) appeared, which were assigned to the CRC stretching vibration modes of C2H2 differing in their adsorbed state. Both photoluminescence and X-ray absorption spectra showed that cuprous ions (Cu+) in CuMFI act as efficient sites for a marked C2H2 adsorption. From the analysis of the latter spectra and the calculational results based on the density functional theory, the formation of dual Cu+center dot center dot center dot(C2H2)center dot center dot center dot Cu+ complexes was indicated for the first time for CuMFI, and such a special configuration of the Cu+ sites contributed to the extremely strong adsorption of C2H2. In contrast, it was necessary for the linear CO2 molecule to take a bent structure to be adsorbed on Cu+ in CuMFI. It was concluded that the difference in the adsorption response of Cu+ in CuMFI towards C2H2 and CO2 is due to the chemistry between the nature of electron donation of Cu+ and the hybrid orbitals of the respective molecules. This work promotes further understanding of the states of active centres in CuMFI for C2H2 activation, as well as for N-2 fixation.

DOI： 10.1039/c000967a

その他リンク： http://orcid.org/0000-0001-5907-3683

Formation mechanism of powder emulsion; evaluating hydrophobic interaction between solid particles at the ari/water interface 査読

K. Igarashi, H. Maruyama, T. Ohkubo, K. Sakai, N. Naito, H. Sakai, M. Abe

材料技術 28 ( 1 ) 8 - 13 2010年

Potential for C-H Activation in CH4 Utilizing a CuMFI-Type Zeolite as a Catalyst 査読

Atsushi Itadani, Hiroyuki Sugiyama, Masashi Tanaka, Takahiro Ohkubo, Takashi Yumura, Hisayoshi Kobayashi, Yasushige Kuroda

JOURNAL OF PHYSICAL CHEMISTRY C 113 ( 17 ) 7213 - 7222 2009年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER CHEMICAL SOC

We have found that a copper ion-exchanged MFI (Mobil Five)-type zeolite, having an ion exchange capacity of 112% (CuMFI-112), exhibits a specific interaction with CH4, even at room temperature. The observed properties are very remarkable compared with those found in the adsorbed amount of sodium ion-exchanged MFI and in the interaction with the sodium ion in MFI as well as in the adsorbed amounts for other types of copper ion-exchanged zeolites. The specificity of Cu+ in MFI is clearly evident. The most remarkable feature of the present system is the distinct appearance of infrared bands (IR) at 2661 and 2619 cm(-1) due to adsorbed CH4 at 300 K and the change in the X-ray absorption fine structure spectra of CuMFI before and after CH4 adsorption at 300 K, indicating the existence of substantial and specific interaction in this system. In addition, calculations based on the density functional theory were carried out by utilizing a Cu-AlSi91O151H66 cluster model, which is made up of a 10-membered ring of CuMFI. As a result, the calculations gave absorption bands that can be explained reasonably by the observed novel IR bands, indicating the existence of two types of eta(2)(H, H)-type interactions between Cu+ and CH4: (1) hydrogen interacted with a Cu cation coordinating to two oxygen atoms near an intersection of straight and sinusoidal channels, and (2) hydrogen interacted with a Cu cation located above a 5-membered ring on a wall of a straight channel. The nature of such bonding can be described by the formation of Cu-C bonds, which causes the deformation the T-d structure of CH4. Such interaction results in a weakening of the C-H bond and thus a lower frequency shift of the C-H bond interacting with Cu+.

DOI： 10.1021/jp807008t

その他リンク： http://orcid.org/0000-0001-5907-3683

Evaluating the formation of powder emulsion on the basis of the fractal properties of nano-ordered solid particles 査読

K. Igarashi, H. Maruyama, T. Ohkubo, K. Sakai, H. Sakai, M. Abe

材料技術 27 ( 1 ) 6 - 13 2009年

カチオン性シランカップリング剤で処理した基板上への酸化チタン薄膜の調製と光触媒特性査読

河野浩輝, 柴田裕史, 大久保貴広, 酒井俊郎, 酒井健一, 酒井秀樹, 阿部正彦

材料技術 26 ( 3 ) 147 - 153 2008年5月

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