Faculty Profiles - TORIMOTO Tsukasa

Papers - TORIMOTO Tsukasa

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Photo-Induced Electron Migrations in the Nano-Cavities of Mesoporous Silica Sensitized by a Cationic Porphyrin Dye Reviewed

Takuya Hirano, Tatsuto Yui, Ken-ichi Okazaki, Tsutomu Kajino, Yoshiaki Fukushima, Haruo Inoue, Katsuhiko Takagi, and Tsukasa Torimoto

J. Nanosci. Nanotechnol. Vol. 9 page： 506-513 2009.1

Photocatalytic Electron Flow through the Interface of Titania Nanosheets and Mesoporous Silica Hybrid Films Reviewed

Tatsuto Yui, Takuya Hirano, Ken-ichi Okazaki, Haruo Inoue, Tsukasa Torimoto, Katsuhiko Takagi

Vol. 207 page： 135-142 2009.1

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

UV-light induced redox reactions between cationic porphyrins (H2TMPyP) and methyl viologen (MV2+) separately incorporated in titania nanosheets (TNS) and cubic-mesoporous silica (MPS) integrated films, respectively, were investigated. In this system, the following two modified hybrids, i.e., the normally stacked (MV2+–TNS)/(H2TMPyP–MPS) on a FTO electrode and the inversely stacked
(H2TMPyP–MPS)/(TNS) films on a FTO electrode were examined. In accordance with the expected electron flowfromH2TMPyP to MV2+, cathodic photocurrentswere observed for the normally stacked film in acetonitrile (CH3CN) under a negative bias voltage of −0.4 V. However, under the influence of a positive bias voltage of +0.3 V, anodic photocurrents were observed even in CH3CN. On the other hand, anodic photocurrents were also observed in water for the normally stacked films at both bias voltages of +0.3 and −0.4V due to photoreduction followed by proton abstraction of the H2TMPyP molecules from H2O within the MPS nano-cavities. In addition, ca. 0.98 mC of the photocurrents were determined in water for the inversely stacked (H2TMPyP–MPS)/(TNS) films without MV2+, of which ca. 50% resulted in the oxidative consumption of H2TMPyP in the MPS cavities.

Photochemical Shape Control of Cadmium Sulfide Nanorods Coated with an Amorphous Silica Thin Layer Reviewed

Tsukasa Torimoto, Masayuki Hashitani, Takahito Konishi, Ken-ichi Okazaki, Tamaki Shibayama, and Bunsho Ohtani

J. Nanosci. Nanotechnol. Vol. 9 page： 495-500 2009.1

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

The surface of cadmium sulfide nanorods was modified by 3-mercaptopropyltrimethoxysilane, followed by the hydrolysis of trimethoxysilyl groups to form a silica shell structure (SiO2/CdS[rod]). Size-selective photoetching was applied to SiO2/CdS[rod] to modify the size of the CdS rod core.
The absorption spectra were blue-shifted by irradiation of monochromatic light, and finally absorption onset agreed with the wavelength of irradiation light. These facts indicated that CdS rod particles were photoetched to smaller ones until the irradiated photons were no longer absorbed by the photoetched particles and that the SiO2 shell layer surrounding the CdS rod core prevented coalescence between photoetched particles. Changes in the wavelength of irradiation light from 488 to 436 nm caused a decrease in rod width from 3.5 to 2.3 nm along with remarkable decrease in the length of rod from 14 to 4.2 nm, suggesting that the photoetching rate was dependent on the kind of crystal faces and that the photocorrosion reactions at the tips of the CdS rod, that is, on (001)
and/or (00¯1) faces, were faster than those on other faces that appeared on the sides of the rod. This technique enabled control of CdS rod shape by selecting the wavelength of irradiation light.

Systematic Studies on Emission Quenching of Cadmium Telluride Nanoparticles Reviewed

Taro Uematsu, Takahiro Waki, Tsukasa Torimoto, and Susumu Kuwabata

J. Phys. Chem. C Vol. 113 ( 52 ) page： 21621-21628 2009

Emission Quench of Water-soluble ZnS–AgInS2 Solid Solution Nanocrystals and Its Application to Chemosensors Reviewed

Taro Uematsu, Shohei Taniguchi, Tsukasa Torimoto and Susumu Kuwabata

Chem. Commun. ( 48 ) page： 7485-7487 2009

Self-Assembly of Ionic Liquid (BMI-PF6)-Stabilized Gold Nanoparticles on a Silicon Surface: Chemical and Structural Aspects Reviewed

Om P. Khatri, Kosaku Adachi, Kuniaki Murase, Ken-ichi Okazaki, Tsukasa Torimoto, Nobuo Tanaka, Susumu Kuwabata, and Hiroyuki Sugimur

Langmuir Vol. 24 page： 7785-7792 2008.7

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

Ultrafine monodisperse gold nanoparticles (AuNPs) were synthesized by an elegant sputtering of gold onto 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF6) ionic liquid. It was found that the BMI-PF6 supramolecular aggregates were loosely coordinated to the gold nanoparticles and were replaceable with thiol molecules. The self-assembly of BMI-PF6-stabilized AuNPs onto a (3-mercaptopropyl)trimethoxysilane (MPS)-functionalized silicon surface in 2D arrays, followed by dodecanethiol (DDT) treatment, have been demonstrated using X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and contact angle measurements. DDT treatment of tethered AuNPs revealed two types of interactions between AuNPs and the MPS -functionalized surface: (a) AuNPs anchor through Au-S chemisorption linkage resulting in strong immobilization and (b) some of the AuNPs are supported by physisorption, driven by BMI-PF6. The attachment of these particles remains unchanged with sonication. The replacement of BMI-PF6 aggregates from physisorbed AuNPs with DDT molecules advances the dilution of their interaction with the M PS -functionalized surface, and they subsequently detach from the silicon surface. The present finding is promising for the immobilization of ionic liquid-stabilized nanoparticles, which is very desirable for electronic and catalytic device fabrication. Additionally, these environmentally friendly AuNPs are expected to replace conventional citrate-stabilized AuNPs.

Photoluminescence Enhancement of ZnS–AgInS2 Solid Solution Nanoparticles Layer-by-layer-assembled in Inorganic Multilayer Thin Films Reviewed

Tatsuya Kameyama, Ken-ichi Okazaki, Yuji Ichikawa, Akihiko Kudo, Susumu Kuwabata, and Tsukasa Torimoto

Chem. Lett. Vol. 37 ( 7 ) page： 700-701 2008.7

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

Multilayer films of layered double hydroxide (LDH) nano-sheets and semiconductor nanoparticles of ZnS-AgInS2 solid solution (ZAIS) or CdS were prepared by a layer-by-layer deposition technique. The photoluminescence properties were remarkably dependent on the stacked structure of the films owing to the energy transfer from CdS to ZAIS nanoparticles.

*Single-step synthesis of gold-silver alloy nanoparticles in ionic liquids by a sputter deposition technique Reviewed

Ken-ichi Okazaki, Tomonori Kiyama, Kaori Hirahara, Nobuo Tanaka, Susumu Kuwabata and Tsukasa Torimoto

Chem. Commun. page： 691-693 2008.2

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

The simultaneous sputter deposition of gold and silver onto ionic liquids formed bimetallic alloy nanoparticles, which exhibited composition-sensitive surface plasmon resonance, the peak wavelength being red-shifted with an increase in the surface area of the gold foil targets sputtered.

Development of new techniques for scanning electron microscope observation using ionic liquid Reviewed

Satoshi Arimoto, Masaharu Sugimura, Hitoshi Kageyamaa, Tsukasa Torimoto, Susumu Kuwabata

Electrochimica Acta Vol. 53 page： 6228-6234 2008

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

Based on our previous discovery that ionic liquid (IL) can be observed by a scanning electron microscope (SEM) without charging the liquid, we have developed several novel techniques for SEM observation. Coating of insulating sample with IL is useful for providing electronic conductivity to the samples like metal or carbon coating by vacuum vapor deposition. In this case, dilution of the IL with appropriate volatile solvent like alcohol is effective for coating thin layer of IL on the sample. As a biological sample, seaweed including IL was attempted to be observed by SEM. A seaweed leaf swollen by water was put in an IL bath and the bath was put in an outgassed desiccator to replace water in the seaweed leaf with IL. The resulting sample gave a SEM image of the swollen seaweed whose thickness was several times larger than dried one. Furthermore, the introduction of the IL in vacuum chamber allowed us to develop the in situ electrochemical SEM observation system. Using this system, we observed changes in polypyrrole film thickness caused by the redox reaction of the film and the electrochemical deposition of silver and its oxidative dissolution. It was also found that the energy dispersive X-ray fluorescence (EDX) analysis was available even for the electrode polarized in IL.

Development of in situ electrochemical scanning electron microscopy with ionic liquids as electrolytes Reviewed

Satoshi Arimoto, Daisuke Oyamatsu, Tsukasa Torimoto, Susumu Kuwabata

CHEMPHYSCHEM Vol. 9 page： 763-767 2008

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

We report that ionic liquids (ILs) can be observed by electron microscopy without any charging of the liquid. Based on this, we present an in situ electrochemical scanning electron microscopy (in situ ECSEM) system. The key technology that enables in situ ECSEM is that charges can be removed from an IL by grounding it with a Pt wire, even if the IL is in an insulating gloss cell. As a first demonstration, we describe the redox reaction of a polypyrrole (PPy) film accompanied by changes in its thickness when it is polarized by the film-deposited Pt electrode in the IL. Further more, energy-dispersive X-ray fluorescence (EDX) analysis can be employed for the electrode polarized in the IL. The component analysis by EDX of PPy in an IL containing K+ as a marker, reveals doping of electrolyte cations into the PPy film upon the latter's reduction and dedoping of cations from the film upon oxidation.

*Facile Synthesis of ZnS-AgInS2 Solid Solution Nanoparticles for a Color-Adjustable Luminophore Reviewed

Tsukasa Torimoto, Tomohiro Adachi, Ken-ichi Okazaki, Miwa Sakuraoka, Tamaki Shibayama, Bunsho Ohtani, Akihiko Kudo, and Susumu Kuwabata

J. Am. Chem. Soc. Vol. 129 ( 41 ) page： 12388-12389 2007.11

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

Nanoparticles of ZnS-AgInS2 solid solution (ZAIS) were synthesized by the thermal decomposition of (AgIn)(x) Zn2(1-x)(S2CN(C2H5)(2)) 4 precursors in a hot oleylamine solution. X-ray powder diffraction analyses revealed that the resulting nanoparticle powders were not a mixture of ZnS and AgInS2 but a ZnS-AgInS2 Solid solution in which the fraction of ZnS was enlarged with a decrease in the value of x, that is, an increase in the content of Zn2+ in the precursors used. The energy gap of ZAIS nanoparticles could be controlled by the composition of solid solution. Intense emission was observed at room temperature, regardless of the kind of the particles, the peak wavelength of PL being blue-shifted from 720 to 540 nm with a decrease in the value of x. The highest quantum yield of ca. 24% was obtained for nanoparticles prepared with x = 0.86, which was much higher than the quantum yields reported for I-III-VI2-based semiconductor nanoparticles, such as CuInS2 and ZnS-CuInS2 solid solution.

Encapsulation of Titanium(IV) Oxide Particles in Hollow Silica for Size-selective Photocatalytic Reactions Reviewed

Shigeru Ikeda, Yoshimitsu Ikoma, Hideyuki Kobayashi, Takashi Harada, Tsukasa Torimoto, Bunsho Ohtani and Michio Matsumura

Chem. Commun. page： 3753-3755 2007.9

*Photocatalytic Syntheses of Azoxybenzene by Visible Light Irradiation of Silica-Coated Cadmium Sulfide Nanocomposites Reviewed

B. Pal, T. Torimoto, K.-i. Okazaki and B. Ohtani

Chem. Commun. ( 5 ) page： 483-485 2007.2

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

Photoirradiation (l=5-436 nm) of a deaerated 2-propanol
aqueous solution containing nitrobenzene and rhodium-loaded
silica-coated cadmium sulfide nanoparticles produced azoxybenzene with relatively high selectivity (68%), the photocatalytic activity being enhanced with a decrease in the size of the semiconductor particle core.

Size-selective Photocatalytic Reactions by Titanium(IV) Oxide Coated with a Hollow Silica Shell in Aqueous Solutions Reviewed

Shigeru Ikeda, Hideyuki Kobayashi, Yoshimitsu Ikoma, Takashi Harada, Tsukasa Torimoto, Bunsho Ohtani and Michio Matsumura

Phys. Chem. Chem. Phys. Vol. 2007 page： 6319-6326 2007.2

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

A novel core-shell composite photocatalyst, commercially available titanium(IV) oxide (TiO2) particles directly incorporated into a hollow amorphous silica shell, was fabricated by successive coating of TiO2 with a carbon layer and a silica layer followed by heat treatment to remove the carbon layer. The composite induced efficient photocatalytic reactions when relatively small substrates were used, such as methanol dehydration and decomposition of acetic acid, without any reduction in the intrinsic activity of original TiO2, but did not exhibit efficient photocatalytic activity for decomposition of large substrates, methylene blue and polyvinyl alcohol. The uniquesize-selective properties of the composites are due to their structural characteristics, i.e., the presence of a pore system and a void space in the silica shell and between the shell and medial TiO2 particles, respectively. The loading of alkylsilyl groups on the surface of the composite led to highly photostable. oatability: the floated sample also induced efficient photocatalytic reaction for decomposition of acetic acid while retaining floatation at the gas/water interface.

One-step Synthesis and Photosensitivity of Size-quantized Cadmium Chalcogenide Nanoparticles Deposited on Porous Zinc Oxide Film Electrodes Reviewed

K.-i. Okazaki, N. Kojima, Y. Tachibana, Susumu K., and T. Torimoto

Chem. Lett. Vol. 36 page： 712-713 2007

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

Size-quantized cadmium chalcogenide nanoparticles were
effectively deposited on a porous zinc oxide particulate film electrode by a one-step hydrothermal method in which an increase in the concentration of 3-mercaptopropionic acid reduced the size of deposited nanoparticles. The photoelectrochemical properties of the resulting electrodes varied depending on the kind of metal chalcogenide nanoparticles deposited and their
size.

CdS Quantum Dots Sensitized TiO2 Sandwich Type Photoelectrochemical Solar Cells

Y. Tachibana, H. Y. Akiyama, Y. Ohtsuka, T. Torimoto, and S. Kuwabata

Chem. Lett. Vol. 36 page： 88-89 2007

Effect of Ionic Surfactants on the Iridescent Color in Lamellar Liquid Crystalline Phase of a Nonionic Surfactant

X. Chen, H. Mayama, G. Matsuo, T. Torimoto, B. Ohtani, and K. Tsujii

J. Colloid Interface Sci. Vol. 305 page： 308-314 2007

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

A nonionic surfactant, n-dodecyl glyceryl itaconate (DGI), self-assembles into bilayer membranes in water having a spacing distance of submicrometer in the presence of small amounts of ionic surfactants, and shows beautiful iridescent color. Ionic surfactants have strong effects on this iridescent system. We have interestingly found that the iridescent color changes with time after mixing DGI and ionic surfactants and the color in equilibrium state changes greatly with concentration of the ionic surfactants. The time-dependent color change results from the transformation of DGI aggregate structure after being mixed with ionic surfactant. It is first found that the iridescent color of this nonionic system can be changed
from red to deep blue by altering the concentration of ionic surfactants added even though the total concentration of surfactant is almost constant. Such large blue shift of the iridescent color in equilibrium state cannot be fully explained by the ordinary undulation theory applied so far for this phenomenon. The flat lamellar sheets tend to curve by increasing the concentration of ionic surfactants to form separated onion-like and/or myelin-like structures. These separated structures of lamellar system result in the decrease of spacing distance between bilayer membranes because
some vacant spaces necessarily appear among these structures.

Double-Beam Photoacoustic Spectroscopic Studies on Transient Absorption of Titanium(IV)Oxide Photocatalyst Powders Reviewed

Naoya Murakami, Orlando Omar Prieto Mahaney, Ryu Abe, Tsukasa Torimoto, and Bunsho Ohtani

J. Phys. Chem. C Vol. 111 page： 11927-11935 2007

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

In situ photoabsorption properties of titanium(IV) oxide (TiO2) powders under continuous ultraviolet irradiation
were investigated by double-beam photoacoustic (PA) spectroscopy. This PA measurement enabled observation
of two kinds of ultraviolet-light-induced intermediate species appearing on various kinds of TiO2 powder samples. Most of the samples (type 1) exhibited photoabsorption due to the production of trivalent titanium (Ti3+) species, while transient absorption assigned to trapped holes or surface peroxy species was also observed for anatase samples with a relatively large specific surface area (type 2). Time-resolved measurements and analyses of the kinetics of photoinduced Ti3+ species suggest that electrons accumulated in type-2 samples have high reactivity toward molecular oxygen compared to type-1 samples. Saturation limits of intensity of the PA signal attributed to Ti3+ species under deaerated conditions in the presence of surface-adsorbed methanol were estimated for both types of samples, and their linear relation with density of Ti3+ species estimated by a conventional photochemical technique was observed. This suggests that the present double-beam PA technique is an alternative feasible method for estimation of density of Ti3+ species, which is a potential measure of density of crystalline defects.

Pyrene-to-porphyrin excited singlet energy transfer in LBLdeposited LDH nanosheets Reviewed

Vol. 11 page： 428 2007

Microscopic Structure of Separately Accommodated Phorphyrins and Viologens in Mesoporous Silica and Titania Nanosheet Hybrid Films Reviewed

Tatsuo Yui, Tsutomu Kajino, Takako Tsuchino, Ken-ichi Okazaki, Tsukasa Torimoto, Yoshiaki Fukushima, and Katsuhiko Takagi

Trans. Mater. Res. Soc. Jap. Vol. 32 page： 449-452 2007

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

The microscopic structures of two nano-structured inorganic films, the one based on titania nanosheets
(TNS) and the other on mesoporous silica (MPS), were investigated. Clear stacking structure of the TNS and MPS films was observed for the XRD, SEM, and TEM analyses. Both porphyrin derivatives and viologens were separately and selectively adsorbed into the MPS nano-cavities and the TNS nano-layers, respectively by means of their absorption and energy-dispersive spectroscopies (EDS).

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Papers - TORIMOTO Tsukasa