研究者詳細 - 大久保　貴広

A facile synthesis of a SnO2/Graphene oxide nano-nano composite and its photoreactivity 査読

Tomoyuki Tajima, Haruko Goto, Masayasu Nishi, Takahiro Ohkubo, Yuta Nishina, Hideaki Miyake, Yutaka Takaguchi

Materials Chemistry and Physics 212 149 - 154 2018年6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 Ltd

A novel SnO2/graphene oxide (GO) nano-nano composite was prepared by a facile sol–gel process. X-Ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and nitrogen adsorption–desorption isotherms measurements confirmed the formation of a SnO2/GO nano-nano composite. The photoreaction of this SnO2/GO nano-nano composite was studied via the photodegradation of rhodamine B (RhB). Interestingly, the degradation mode of RhB in oxygen-saturated solution is photocatalytic reaction, but the degradation mode in argon-saturated solution is not photocatalytic reaction.

DOI： 10.1016/j.matchemphys.2018.03.046

Selective molecular-gating adsorption in a novel copper-based metal–organic framework 査読

Atsushi Kondo, Taiki Yashiro, Naoya Okada, Shotaro Hiraide, Takahiro Ohkubo, Hideki Tanaka, Kazuyuki Maeda

Journal of Materials Chemistry A 6 ( 14 ) 5910 - 5918 2018年4月

Why do zeolites induce an unprecedented electronic state on exchanged metal ions? 査読

Akira Oda, Takahiro Ohkubo, Takashi Yumura, Hisayoshi Kobayashi, Yasushige Kuroda

PHYSICAL CHEMISTRY CHEMICAL PHYSICS 19 ( 36 ) 25105 - 25114 2017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：ROYAL SOC CHEMISTRY

Understanding the exact position and the detailed role of the Al array in zeolites is essential for elucidating the origin of unique properties that can be derived from the metal-ion exchanged in zeolite samples and for designing zeolite materials with high efficiency in catalytic and adsorption processes. In this work, we investigate, for the first time, the important role of the Al array in the reactivity observed on the metal-ion exchanged in zeolites on the basis of the calculation method by utilizing the spontaneous heterolytic cleavage of H-2 observed experimentally on the Zn2+-ion exchanged in MFI-type zeolites (Zn2+-MFI) as the model reaction. In the case of calculation, two main types of models for considering the Al positions in MFI-type zeolites were adopted: in the first type, the Al atoms with appropriate distances are aligned in the circumferential direction of the straight channel (abbreviated as a circumferentially arrayed Al-Al site); in the second type, the nearest neighbouring Al atoms with appropriate distances are directed toward the straight channel axis (abbreviated as a channel directionally arrayed Al-Al site). Results indicated that the Al-array direction governs the reactivity of Zn2+-MFI. The former type of array well explains the experimental fact that spontaneous and irreversible heterolysis of H-2 takes place on Zn2+-MFI, even at room temperature, whereas the latter type of array is less reactive; high activation energy is required for the heterolytic cleavage of H-2 (ca. > 70 kJ mol(-1)). A detailed analysis of the geometric and electronic structures of a series of Zn2+-MFI models with various Al-array directions clarified the following facts: the circumferentially arrayed Al-Al site induces an inevitable environment around the Zn2+ site, with the simultaneous existence of both a Lewis acid point (coordinatively unsaturated and distorted Zn2+) and a Lewis base point (the lattice oxygen atom juxtaposed with exchanged Zn2+, which participates in the activation of H-2: O-jL). It is the circumferentially arrayed Al-Al atoms that confer acidic and basic nature on the metal ion and the lattice oxygen atom (OjL), and ultimately trigger the heterolytic dissociation of H-2, even at 300 K.

DOI： 10.1039/c7cp02669b

Identification of a Stable Zn-II-Oxyl Species Produced in an MFI Zeolite and Its Reversible Reactivity with O-2 at Room Temperature 査読

Akira Oda, Takahiro Ohkubo, Takashi Yumura, Hisayoshi Kobayashi, Yasushige Kuroda

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 56 ( 33 ) 9715 - 9718 2017年8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：WILEY-V C H VERLAG GMBH

Although a terminal oxyl species bound to certain metal ions is believed to be the intermediate for various oxidation reactions, such as O-O bond generation in photosystem II (PSII), such systems have not been characterized. Herein, we report a stable Zn-II-oxyl species induced by an MFI-type zeolite lattice and its reversible reactivity with O-2 at room temperature. Its intriguing characteristics were confirmed by in situ spectroscopic studies in combination with quantum-chemical calculations, namely analyses of the vibronic Franck-Condon progressions and the ESR signal features of both Zn-II-oxyl and Zn-II-ozonide species formed during this reversible process. Molecular orbital analyses revealed that the reversible reaction between a ZnII-oxyl species and an O-2 molecule proceeds via a radical O-O coupling-decoupling mechanism; the unpaired electron of the oxyl species plays a pivotal role in the O-O bond generation process.

DOI： 10.1002/anie.201702570

Tubular nitrogen-doped TiO2 samples with efficient photocatalytic properties based on long-lived charge separation under visible-light irradiation: synthesis, characterization and reactivity 査読

Yoshikazu Hirose, Atsushi Itadani, Takahiro Ohkubo, Hideki Hashimoto, Jun Takada, Shigeharu Kittaka, Yasushige Kuroda

DALTON TRANSACTIONS 46 ( 13 ) 4435 - 4451 2017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：ROYAL SOC CHEMISTRY

A nitrogen-doped TiO2 sample was prepared at 413 K by direct hydrothermal treatment of titanium isopropoxide in an aqueous solution of NH3. This new material has a large specific surface area of ca. 220 m(2) g(-1) because of its tubular structure and it exhibits a prominent absorption feature in the region between 400 and 650 nm. It responds strongly to light in the visible region, which is key to its potential performance as a photocatalyst that may improve the efficiency for utilization of solar energy. Actually, this sample exhibits very efficient activity in the decomposition of CH3COOH under visible light among the samples prepared. This effective photocatalysis of the present sample was substantiated by characteristic spectroscopic features, such as: (1) an optical absorption band with lambda > 400 nm because of the doped nitrogen species; (2) the formation of EPR-active, long-lived N-. and O(2)(-)species, as well as N-2(-) species, under visible-light irradiation in the O-2 or N-2 adsorption process at 300 K by way of the monovalent nitrogen ions in the bulk (both substitutional and interstitial); (3) the existence of IR-active O-2 species adsorbed on the nitrogen-doped TiO2 sample even without light irradiation; and (4) an XPS N-1s band around 399.6 eV that is assignable to the N- species. The amounts of N-. and O-2(-) species formed in the nitrogen-doped TiO2 sample under visible-light irradiation correlated well with the levels of reactivity observed in the decomposition of CH3COOH on the samples with varying amounts and types of doped nitrogen species. We conclude that the photoactive N-. and O-2(-) species created in the present sample are responsible for the decomposition of organic materials assisted by visible light irradiation. These features may be attributable to the interface between the sample's tubular structure and anatase with poor crystallinity, which probably causes the resistance to the recombination of electron-hole pairs formed by irradiation.

DOI： 10.1039/c6dt04914a

微生物由来鞘状酸化鉄を利用した多孔質炭素材料および炭素－酸化鉄複合材料の作製査読

西村維心, 後藤和馬, 日浦登和, 川村仁美, 橋本英樹, 松本修治, 高田潤, 粕壁隆敏, 西原洋知, 後藤秀徳, 大久保貴広, 石田祐之

炭素 280 188 - 197 2017年

Material Exhibiting Efficient CO2 Adsorption at Room Temperature for Concentrations Lower Than 1000 ppm: Elucidation of the State of Barium Ion Exchanged in an MFI-Type Zeolite 査読

Atsushi Itadani, Akira Oda, Hiroe Torigoe, Takahiro Ohkubo, Mineo Sato, Hisayoshi Kobayashi, Yasushige Kuroda

ACS APPLIED MATERIALS & INTERFACES 8 ( 13 ) 8821 - 8833 2016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

Carbon dioxide (CO2) gas is well-known as a greenhouse gas that leads to global warming. Many efforts have been made to capture CO2 from coal-fired power plants, as well as to reduce the amounts of excess CO2 in the atmosphere to around 400 ppm. However, this is not a simple task, particularly in the lower pressure region than 1000 ppm. This is because the CO2 molecule is chemically stable and has a relatively low reactivity. In the present study, the CO2 adsorption at room temperature on MFI-type zeolites exchanged with alkaline-earth-metal ions, with focus on CO2 concentrations <1000 ppm, was investigated both experimentally and by calculation. These materials exhibited a particularly efficient adsorption capability for CO2, compared with other presented samples, such as the sodium-form and transition-metal ion-exchanged MFI-type zeolites. Ethyne (C2H2) was used as a probe molecule. Analyses were carried out with IR spectroscopy and X-ray absorption, and provided significant information regarding the presence of the M2+-O2--M2+ (M2+: alkaline-earth-metal ion) species formed in the samples. It was subsequently determined that this species acts as a highly efficient site for CO2 adsorption at room temperature under very low pressure, compared to a single M2+ species. A further advantage is that this material can be easily regenerated by a treatment, e.g., through the application of the temperature swing adsorption process, at relatively low temperatures (300-473 K).

DOI： 10.1021/acsami.6b00909

Possibility of Copper-Ion-Exchanged MFI-Type Zeolite as C-H Bond Activation Material for Propane and the Driving Force for Activation 査読

Atsushi Itadani, Yusuke Sogawa, Akira Oda, Takahiro Ohkubo, Takashi Yumura, Hisayoshi Kobayashi, Mineo Sato, Yasushige Kuroda

JOURNAL OF PHYSICAL CHEMISTRY C 119 ( 37 ) 21483 - 21496 2015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 dehydrogenation of propane (C3H8) utilizing solid catalysts is expected to be a promising method for producing propene (C3H6) selectively and economically. Propene is useful as a raw material to produce other valuable materials. To push forward the dehydrogenation reaction of C3H8, it is essential to find catalysts that work effectively in the activation of the C-H bonds in C3H8. To this end, we investigated the interaction of C3H8 with the copper-ion-exchanged MFI-type zeolite (CuMFI) at room temperature. The C3H8 adsorption properties of CuMFI were remarkable, compared with those of the sodium-form MFI-type zeolite (NaMFI); CuMFI exhibited irreversible adsorption, even at room temperature, whereas NaMFI exhibited reversible adsorption. Correspondingly, the CuMFI had an adsorption energy of 110 kJ mol(-1) in the initial adsorption region, whereas the NaMFI had an adsorption energy of 50 kJ mol(-1). Furthermore, a peculiar feature was observed in the appearance of the characteristic infrared (IR) absorption bands at 2740, 2659, and 2624 cm(-1) and, particularly, the band that appeared at 2555 cm(-1). They were noticeably shifted toward the lower wavenumber side, compared with the C-H vibration bands for a gaseous C3H8 molecule. This was a result of the interaction of C3H8 with the Cu+ ions formed in CuMFI. The application of density functional theory calculations to the model, comprising the interaction between the dual-Cue site in CuMFI and C3H8, well explains the observation of the appearance of these four types of bands toward the lower wavenumber side and also the adsorption energy. The cause is the dominant contribution of the back-donation from Cu+ to C3H8, rather than the donation from C3H8 to Cu+, which results in a weakening of the C-H bonds in the C3H8 molecule. The Cu site taking a dimeric structure, not various types of single-Cu+ sites, plays a key role in activating C3H8 effectively, even at around 300 K. Results of this study should contribute to not only understanding the critical role of the dimeric Cu+ species in MFI but also developing new materials with superior activity in the activation of the C-H bond in alkanes.

DOI： 10.1021/acs.jpcc.5b05577

Synthesis of an unexpected [Zn-2](2+) species utilizing an MFI-type zeolite as a nano-reaction pot and its manipulation with light and heat 査読

Akira Oda, Takahiro Ohkubo, Takashi Yumura, Hisayoshi Kobayashi, Yasushige Kuroda

DALTON TRANSACTIONS 44 ( 21 ) 10038 - 10047 2015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

Compared with mercury, the existence of [Zn-2](2+) species is rare. We succeeded in preparing a stable [Zn-2](2+) species by utilizing an MFI-type zeolite as a nano-reaction pot, which was confirmed using XAFS spectroscopy: the bands at R = 2.35 angstrom due to the Zn+-Zn+ scattering and at 9660.7 eV due to the 1s-sigma* (the anti-bonding orbital comprised of the 4s-4s orbital) transition of the [Zn-2](2+) species. This species also gives the characteristic band around 42 000 cm(-1) due to its sigma-sigma* transition. Furthermore, UV-irradiation corresponding to the sigma-sigma* transition causes the bond dissociation, forming two unprecedented Zn+ ions, and detached Zn+ ions were recombined through heat-treatment at 573 K: [Zn+-Zn+] reversible arrow 2Zn(+). These processes were reproduced by applying the DFT calculation method to the assumed triplet, sigma(alpha)-sigma*(alpha), structure formed on the M7-S2 site with the specific Al array in the MFI-type zeolite. Research into the specific field using zeolites to synthesize "ultra-state ions" is very promising.

DOI： 10.1039/c5dt01088h

An Important Factor in CH4 Activation by Zn Ion in Comparison with Mg Ion in MFI: The Superior Electron-Accepting Nature of Zn2+ 査読

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

JOURNAL OF PHYSICAL CHEMISTRY C 118 ( 28 ) 15234 - 15241 2014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：AMER CHEMICAL SOC

We present clear IR and density functional theory (DFT) evidence demonstrating that the electron-accepting nature of Zn2+ ion exchanged in MFI-type zeolite (ZnMFI) plays a dominant role in CH4 activation. The IR study revealed that the heterolytic dissociation of CH4 takes place on the Zn2+ ion exchanged in MFI under a CH4 atmosphere even near room temperature, whereas a similar reaction scarcely occurred on Mg2+ ion exchanged in MFI, although the ionic radius and charge of Mg2+ are almost the same as those of Zn2+. These data indicate that the dissociation reaction of CH4 on Zn2+ in MFI is facilitated not only by the electrostatic interaction but also by the electron-transfer interaction. This interpretation was clearly evidenced by the observed v(1) mode of the C-H symmetric stretching vibration, i.e., a larger band shift toward lower wavenumbers, for the molecular CH4 adsorbed on ZnMFI, compared with those for a gaseous CH4 molecule. Additional experiments were also performed by the IR method utilizing CO as a probe molecule that has an electron-donating nature. All experimental data presented were successfully explained in terms of the superior electron-accepting nature of Zn2+ exchanged in MFI. Furthermore, the DFT calculation method completely explained all experimental data by adopting the M7S2 model, which was truncated from the ZnMFI structure; the electron-accepting nature is dominant in the heterolytic activation of CH4 in the Zn2+ ion in MFI in comparison with that of Mg2+ exchanged at the same site. We have thus shown that the electron-transfer interaction between Zn2+ and CH4 plays a key role in the heterolytic CH4 activation process: the sigma donation from the sigma(C-H) orbital of CH4 toward the Zn 4s orbital through overlapping with each orbital.

DOI： 10.1021/jp5013413

Biosynthesis of elliptical hematite microparticles and their photocatalytic performance 査読

B. Ahmmad, K. Kanomata, F. Hirose, J. Kurawaki, T. Ohkubo

Rangsit Journal of Arts and Sciences 4 ( 1 ) 31 - 38 2014年

Success in Making Zn+ from Atomic Zn-0 Encapsulated in an MFI-Type Zeolite with UV Light Irradiation 査読

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

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 135 ( 49 ) 18481 - 18489 2013年12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

For the first time, the paramagnetic Zn+ species was prepared successfully by the excitation with ultraviolet light in the region ascribed to the absorption band resulting from the 4s-4p transition of an atomic Zn-0 species encapsulated in an MFI-type zeolite. The formed species gives a specific electron spin resonance band at g = 1.998 and also peculiar absorption bands around 38,000 and 32,500 cm(-1) which originate from 4s-4p transitions due to the Zn+ species with paramagnetic nature that is formed in MFI. The transformation process (Zn-0 -> Zn+) was explained by considering the mechanism via the excited triplet state (P-3) caused by the intersystem crossing from the excited singlet state produced through the excitation of the 4s-4p transition of an atomic Zn-0 species grafted in MFI by UV light. The transformation process was well reproduced with the aid of a density functional theory calculation. The thus-formed Zn+ species which has the doublet spin state exhibits characteristic reaction nature at room temperature for an O-2 molecule having a triplet spin state in the ground state, forming an eta(1) type of Zn2+-O-2(-) species. These features clearly indicate the peculiar reactivity of Zn+ in MFI, whereas Zn-0-(H+)(2)MFI hardly reacts with O-2 at room temperature. The bonding nature of [Zn2+-O-2(-)] species was also evidenced by ESR measurements and was also discussed on the basis of the results obtained through DFT calculations.

DOI： 10.1021/ja4077342

Mechanism of CH4 activation on a monomeric Zn2+-ion exchanged in MFI-Type zeolite with a specific Al arrangement: Similarity to the activation site for H2 査読

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

Journal of Physical Chemistry C 117 ( 38 ) 19525 - 19534 2013年9月

記述言語：英語掲載種別：研究論文（学術雑誌）

In this work, we used both experimental and density functional theory (DFT) calculation methods to examine the mechanism of CH4 activation taking place on the Zn2+ ion exchanged MFI-type zeolite (ZnMFI). The heterolytic dissociation of CH4 on ZnMFI around 300 K was observed experimentally, causing the appearance of IR bands at 3615, 2930, and 2892 cm-1. The first band can be assigned to the OH stretching vibration associated with the formation of the Brønsted acid site and the latter to the C-H stretching modes ascribable to the -[ZnCH3]+ species. Combining the IR spectroscopy with a DFT calculation, it is apparent that the heterolytic C-H bond dissociation of CH4 has an activation energy of 15 kJ mol-1 and takes place on a monomeric Zn2+ at the M7S2 site. The M7S2 site has a specific Al arrangement in MFI and exhibits a pronounced reactivity for the H-H bond cleavage of H2, even at room temperature. In addition, to our knowledge, we are the first to succeed in explaining the dissociation process of CH4 by applying natural bond orbital (NBO) and interaction localized orbital (ILO) analyses to the present system
the donation interaction from the CH4-σ(C- H) orbital to the Zn-4s orbital triggers the cleavage of the C-H bond of CH 4 under mild conditions. © 2013 American Chemical Society.

DOI： 10.1021/jp4065517

Further evidence for the existence of a dual-Cu+ site in MFI working as the efficient site for C2H6 adsorption at room temperature 査読

Atsushi Itadani, Yusuke Sogawa, Akira Oda, Hiroe Torigoe, Takahiro Ohkubo, Yasushige Kuroda

Langmuir 29 ( 31 ) 9727 - 9733 2013年8月

記述言語：英語掲載種別：研究論文（学術雑誌）

We have recently clarified the following point: a dual-type site, which is composed of a pair of monovalent copper ions (Cu+) formed in a copper-ion-exchanged MFI-type zeolite (CuMFI), functions as the active center for strong ethane (C2H6) adsorption even at room temperature rather than a single-type site composed of a Cu+ ion. However, the character of the dual-Cu+ site in a CuMFI is not yet fully understood. In this study, we have elucidated the nature of the active sites for C2H6 based on infrared (IR) and calorimetric data. On the basis of the results obtained, we came to the conclusion that the dual-Cu+ site composed of Cu+ ions giving the adsorption energy of 100 kJ mol-1 and the absorption band at 2151 cm -1 for carbon monoxide (used as a probe molecule) at room temperature functions as an adsorption site for C2H6. We also evaluated, for the first time, the interaction between the dual-Cu+ site and C2H6 energetically, by the direct measurement of heat of adsorption. The value of 67 kJ mol-1 that we recorded was higher than that for the single-Cu+ site in this sample and also for other samples, such as NaMFI and HMFI. © 2013 American Chemical Society.

DOI： 10.1021/la4018568

Highly compressed nanosolution restricted in cylindrical carbon nanospaces 査読

Masayasu Nishi, Takahiro Ohkubo, Kazuma Tsurusaki, Atsushi Itadani, Bashir Ahmmad, Koki Urita, Isamu Moriguchi, Shigeharu Kittaka, Yasushige Kuroda

Nanoscale 5 ( 5 ) 2080 - 2088 2013年3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）

We shed light on the specific hydration structure around a zinc ion of nanosolution restricted in a cylindrical micropore of single-wall carbon nanotube (SWNT) by comparison with the structure restricted in a cylindrical mesopore of multi-wall carbon nanotube (MWNT) and that of bulk aqueous solution. The average micropore width of open-pore SWNT was 0.87 nm which is equivalent to the size of a hydrated zinc ion having 6-hydrated water molecules. We could impregnate the zinc ions into the micropore of SWNT with negligible amounts of ion-exchanged species on surface functional groups by the appropriate oxidation followed by heat treatment under an inert condition. The results of X-ray absorption fine structure (XAFS) spectra confirmed that the proportion of dissolved species in nanospaces against the total adsorbed amounts of zinc ions on the open-pore SWNT and MWNT were 44 and 61%, respectively, indicating the formation of a dehydrated structure in narrower nanospaces. The structure parameters obtained by the analysis of XAFS spectra also indicate that the dehydrated and highly compressed hydration structure can be stably formed inside the cylindrical micropore of SWNT where the structure is different from that inside the slit-shaped micropore whose pore width is less than 1 nm. Such a unique structure needs not only a narrow micropore geometry which is equivalent to the size of a hydrated ion but also the cylindrical nature of the pore. © 2013 The Royal Society of Chemistry.

DOI： 10.1039/c2nr33681b