研究者詳細 - 鳥本　司

論文 - 鳥本　司

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Electric-Field-Induced Changes in Absorption and Emission Spectra of CdS Nanoparticles Doped in a Polymer Film

Y. Ohara, T. Nakabayashi, K. Iwasaki, T. Torimoto, B. Ohtani, T. Hiratani, K. Konishi, N. Ohta

J. Phys. Chem. B 110 巻頁： 20927-20936 2006年

記述言語：英語掲載種別：研究論文（学術雑誌）

Electric-field-induced changes in absorption and emission spectra of colloidal CdS nanoparticles ranging in size from 1.0 to 5.0 nm in diameter have been measured by using electric field modulation spectroscopy. The analysis of the electroabsorption spectra indicates that the dipole moment in the first exciton state becomes larger with increasing particle size. The presence of the large dipole moment following photoexcitation into the first exciton band suggests that the CdS nanoparticles have large CT character in the first exciton state. The quantum yields both of the exciton emission and of the trap emission are markedly reduced by application of an electric field. On the basis of the direct measurements of the field-induced change in emission decay profile, it is suggested that the field-induced de-enhancement of these emission yields results from the fieldinduced decreases both in lifetime and in initial population of each emitting state. It is also found that the emission intensity of CdS nanoparticles increases under the UV light irradiation in air and decreases in a vacuum condition and that fluorescence lifetime in the former case is longer than that in the latter. This enhancement and de-enhancement process in emission intensity is almost reversible at least in several cycles.

Ligand-Free Platinum Nanoparticle Encapsulated in a Hollow Porous Carbon Shell as a Highly Active Heterogeneous Catalyst in Hydrogenation Reaction

S. Ikeda, S. Ishino, T. Harada, N. Okamoto, T. Sakata, H. Mori, S. Kuwabata, T. Torimoto, M. Matsumura

Angew. Chem. Int. Ed. 45 巻頁： 7063-7066 2006年

Photochemical Electron Transfer through the Interface of Hybrid Films of Titania Nano-Sheets and Mono-Dispersed Spherical Mesoporous Silica Particles

T. Yui, Y. Kobayashi, Y. Yamada, T. Tsuchino, K. Yano, T. Kajino, Y. Fukushima, T. Torimoto, H. Inoue, and K. Takagi

Phys. Chem. Chem. Phys. 8 巻頁： 4585-4590 2006年

記述言語：英語掲載種別：研究論文（学術雑誌）

Photochemical Electron Transfer (ET) between an organic dye, the porphyrin derivative TMPyP, and an electron acceptor, methyl viologen MV2+, have been investigated at the interface of two different inorganic films, i.e., layered titania nano-sheets (TNS) and a monolayer film of spherical and mono-dispersed mesoporous silica (sMPS) particles (ca. 0.5 mm). TMPyP ions were intercalated within the sMPS nano-cavities to form (TMPyP–sMPS) while MV2+ ions were intercalated into the TNS interlayers to form (MV2+–TNS). The (TMPyP–sMPS) and (MV2+–TNS) films were then stacked on a silica substrate in this order to form a (MV2+–TNS)/(TMPyP–sMPS) film and, upon UV light irradiation, ET could be induced. However, when this
film was stacked inversely, i.e., for the (TMPyP–sMPS)/(MV2+–TNS) films on a silica substrate, no photoinduced ET were observed. Interestingly, however, even for this photo-inactive inversely stacked film, ET could be generated by inserting a gold vapor-deposited layer between the
(MV2+–TNS) and (TMPyP–sMPS) films. The conjugation conditions at the interface of the inversely stacked (TMPyP–sMPS)/(MV2+–TNS) hybrid film were, thus, confirmed to strongly affect the photoinduced electron transfers and their efficiencies.

Analysis of Quantum Dot Fluorescence Coupled with a Microsphere Resonator

H. Takashima, Hideki Fujiwara, J.-i. Hotta, S. Takeuchi, K. Sasaki, S.-y. Murakami, T. Torimoto, B. Ohtani

Jap. J. Appl. Phys. 45 巻頁： 6917-6921 2006年

記述言語：英語掲載種別：研究論文（学術雑誌）

The emission spectrum of CdSe/ZnS quantum dots adhering to the surface of a microsphere resonator is measured and
discussed. Only certain peaks are observed, and the order numbers of the modes (l = 5 to 7) of the observed peaks are
different from those previously reported (l = 1 and 2). [Nano Lett. 1 (2001) 399]. A detailed analysis is presented using the cavity mode efficiency , which is a function of surface roughness, the absorption coefficient of the quantum dots, and mode parameters. The difference between the observed order number modes is explained to be due to the ratio of the rate of absorption by the quantum dots to that of the leakage rates of the modes. The surface roughness of a quantum-dot-coated microsphere and the absorption coefficient of the quantum dots on the sphere are estimated in the analysis.

Photochemical Fine-Tuning of Luminescent Color of Cadmium Selenide Nanoparticles: Fabricating a Single-Source Multi-Color Luminophore

T. Torimoto, S.-y. Murakami, M. Sakuraoka, K. Iwasaki, K.-i. Okazaki, T. Shibayama, and B. Ohtani

J. Phys. Chem. B 110 巻頁： 13314-13318 2006年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Size-selective photoetching was applied to silica-coated cadmium selenide (SiO2/CdSe) nanoparticles to precisely control their photoluminescence properties. The absorption spectra of CdSe was blue-shifted by irradiation of monochromatic light, and finally, the absorption onset agreed with the wavelength of irradiation light, indicating that CdSe particles were photoetched to smaller ones until the irradiated photons were not absorbed by the photoetched particles and that the SiO2 shell layer surrounding the CdSe core prevented coalescence between the photoetched particles. Although as-prepared SiO2/CdSe did not exhibit photoluminescence, the application of size-selective photoetching to SiO2/CdSe resulted in the development of the band gap emission, with the degree being enhanced with progress of the photoetching. The peak wavelength of photoluminescence decreased with a decrease in the wavelength used for the photoetching, so that the
luminescence color could be tuned between red and blue. Partial photoetching of SiO2/CdSe nanoparticle
films produced intense band gap emission of CdSe at the photoetched area, while the remainder of the SiO2/
CdSe films did not exhibit detectable photoluminescence, resulting in the formation of a clear photoluminescence
image under UV irradiation. This technique makes it possible to produce a multicolored photoluminescence image by irradiation with monochromatic lights having various wavelengths using a single source material.

Photoacoustic Spectroscopic Analysis of Photoinduced Change in Absorption of Titanium(IV) Oxide Photocatalyst Powders: A Novel Feasible Technique for Measurement of Defect Density

N. Murakami, O. O. P. Mahaney, T. Torimoto, and B. Ohtani

Chem Phys. Lett. 426 巻頁： 204-208 2006年

記述言語：英語掲載種別：研究論文（学術雑誌）

Photoabsorption properties of titanium(IV) oxide powders were investigated by photoacoustic (PA) spectroscopy. The photoacoustic spectra obtained under steady-state ultraviolet irradiation showed appearance and growth of two kinds of PA signal bands, which were attributable to trivalent titanium species (Ti3+) and trapped holes or surface peroxide species. The saturation limit of the PA signal was estimated by analyzing the time course of Ti3+ signals and compared to the density of Ti3+ determined by a photochemical method. The results suggest that the photoacoustic spectroscopic technique is a feasible alternative method for estimation of Ti3+ as an empirical measure of defect density.

Fabrication of Jingle-Bell-Shaped Core–Shell Nanoparticulate Films and Molecular-Size-Responsive Photoluminescence Quenching of Cadmium Sulfide Cores 査読有り

K. Iwasaki, T. Torimoto, T. Shibayama, T. Nishikawa, and B. Ohtani

Small 2 巻頁： 854-858 2006年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

A monoparticulate layer assembly of silica (SiO2)-coated cadmium sulfide (CdS) nanoparticles (SiO2/CdS) was prepared at an air-water interface and accumulated as thin films on solid substrates by the Langmuir-Blodgett technique. Size-selective photoetching of the CdS core by irradiation of monochromatic light induced a blue shift of diffuse reflectance spectra of the nanoparticulate films, indicating the formation of jingle-bell-shaped CdS core-SiO2 shell nanoparticles in the film. Photoluminescence of thus-photoetched SiO2/CdS nanoparticulate films was quenched by the addition of trialkylamines, the degree being dependent on their molecular size, while little change in the emission intensity was observed in the original films, regardless of the size of trialkylamines added. These facts were attributable to the molecular-size-selective penetration of quencher molecules from the bulk solution to the void space through the pores of the SiO2 shell of the jingle-bell-shaped nanoparticles.

Observation of Ionic Liquid by Scanning Electron Microscope 査読有り

S. Kuwabata, A. Kongkanand, D. Oyamatsu, and T. Torimoto

Chem. Lett. 35 巻頁： 600-601 2006年

Surface modification of photoluminescent CdS nanocrystals inducing spontaneous phase transfer reaction 査読有り

S. Kuwabata, K. Sato, S. Hattori, T. Chiba, K. Ueda-Sarson, Y. Tachibana, and T. Torimoto

Chem. Lett. 34 巻 ( 9 ) 頁： 1300-1301 2005年9月

記述言語：英語掲載種別：研究論文（学術雑誌）

A facile one-step method to modify the surface of luminescent US nanocrystals by alkylamines, without their luminescence intensity loss, was established. The interfacial modification inducing spontaneous transfer of the US from an aqueous to a non-polar organic phase was found to be controlled simply by choosing the alkyl group of the amine. Analysis of the absorption and emission spectra revealed the phase transfer yield of ca. 100%.

Synthesis of metal-cadmium sulfide nanocomposites using jingle-bell-shaped core-shell photocatalyst particles 査読有り

B. Pal, T. Torimoto, K. Iwasaki, T. Shibayama, H. Takahashi, and B. Ohtani

J. Appl. Electrochem. 35 巻 ( 7-8 ) 頁： 751-756 2005年7月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Photocatalytic deposition of gold (Au) and silver (Ag) nanoparticles was investigated using jingle-bell-shaped silica (SiO2)-coated cadmium sulfide (CdS) nanoparticles (SiO2/CdS), which each had a void space between the CdS core and SiO2 shell, as a photocatalyst. A size-selective photoetching technique was used to prepare the jingle bell nanostructure of SiO2/CdS. Nanoparticles of Au and Ag were deposited by irradiation of the photoetched SiO2/CdS in the presence of the corresponding metal complexes under deaerated conditions. Chemical etching of Au-deposited particles enabled the selective removal of CdS without any influence on the surface-plasmon absorption of Au. TEM analyses of the resulting particles suggested that some particles were encapsulated in hollow SiO2 particles, while other Au particles were deposited on the outer surface of the SiO2 shell. Emission spectra of the photoetched SiO2/CdS showed that the metal deposition developed a broad emission with a peak around 650 nm originating from surface defect sites, the degree being dependent on the kind of metal nanoparticles and their amount of deposition. This fact can be explained by the formation of metal-CdS binary nanoparticles having defect sites at the interface between metal and CdS.

Photocatalytic preparation of encapsulated gold nanoparticles by jingle-bell-shaped cadmium sulfide-silica nanoparticles 査読有り

B. Pal, T. Torimoto, S. Ikeda, T. Shibayama, K. Sugawara, H. Takahashi, and B. Ohtani,

Top. Cat. 35 巻 ( 3-4 ) 頁： 321-325 2005年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Gold (Au) nanoparticles were deposited inside silica: (SiO2) shells containing cadmium sulfide (CdS) nanoparticles through photocatalytic reduction of potassium dicyanogold(I) by CdS. Photocatalytic Au deposition occurred only when core-shell nanoparticles having a void space between the core and shell, i.e., a jingle-bell-shaped structure, were used. These core-shell nanoparticles were prepared by size-selective photoetching of SiO2 -covered CdS nanoparticles. The size of Au nanoparticles could be controlled by adjustment of the void space in SiO2-covered CdS. Dissolution of CdS by acid treatment from the Au-deposited jingle-bell nanoparticles did not have any effect on the surface-plasmon absorption by Au. These facts indicate that Au nanoparticles of adjustable size can be prepared in an SiO2 shell that prevents mutual coalescence of Au nanoparticles but allows permeation of molecules and ions.

Size and structure-dependent photocatalytic activity of jingle-bell-shaped silica-coated cadmium sulfide nanoparticles for methanol dehydrogenation 査読有り

B. Pal, T. Torimoto, K. Iwasaki, T. Shibayama, H. Takahashi, and B. Ohtani

J. Phys. Chem. B 108 巻 ( 48 ) 頁： 18670-18674 2004年12月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Silica-coated cadmium sulfide nanoparticles (SiO2/CdS) having a jingle-bell structure were prepared via size-selective photoetching and were used as photocatalysts for dehydrogenation of methanol. Irradiation Of SiO2/ CdS suspended in an aqueous solution containing methanol induced the liberation of hydrogen (1-12), the amount of which increased linearly with increase in the time of irradiation. The observed stable photocatalytic activity was attributed to the prevention of coalescence between CdS core particles by the surrounding SiO2 shells during the photocatalytic reaction. The rate of H, liberation increased with decrease in the wavelength of irradiation light for the size-selective photoetching, that is, the smaller the size of the CdS core, the higher the rate of H-2 liberation, probably because of increased reduction and oxidation abilities of CdS as a result of decrease in their particle size, that is, size quantization effect. Rhodium photodeposited on SiO2/CdS worked as a cocatalyst for the enhancement of dehydrogenation. The photocatalytic activity was reduced by increase in shell thickness because of a decrease in the rate of penetration of chemical species or the transfer of electrons and holes through the SiO2 layer. Also, the close contact between the core and shell retarded the photocatalytic reaction, indicating that the surface of the CdS core for methanol dehydrogenation was covered with a SiO2 shell layer. The results indicate that the jingle-bell-shaped SiO2/CdS nanoparticles can be an efficient and stable photocatalyst with a flexibly tunable structure, in contrast to s urface- modified CdS particles prepared by a conventional technique.

Preparation method allowing self-isolation of CdS nanocrystals emitting intense band-gap luminescence 査読有り

S. Kuwabata, K. Ueda-Sarson, and T. Torimoto

Chem. Lett. 33 巻 ( 10 ) 頁： 1344-1345 2004年8月

Preparation and characterization of water-soluble jingle-bell-shaped silica-coated cadmium sulfide nanoparticles 査読有り

K. Iwasaki, T. Torimoto, T. Shibayama, H. Takahashi, and B. Ohtani

J. Phys. Chem. B 108 巻 ( 32 ) 頁： 11946-11952 2004年8月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Treatment of surface silanol groups with hydrophilic compounds enabled silica-coated cadmium sulfide (SiO2/CdS) nanoparticles of core-shell morphologies to be dissolved in a water/methanol mixture. Size-selective photoetching of the particles was performed by irradiation with monochromatic light at 458 nm, resulting in a blue shift of its absorption onset because of the decreasing size of the CdS. TEM analyses revealed that the SiO2 shell structure was not shrunken by photoetching and that a void space (ca. 2.3 nm) was formed between the US core and the SiO2 shell to give a jingle-bell structure. The emission spectra of photoetched particles showed the development of band-gap emission when cadmium ion (Cd2+) was added and the pH was adjusted to 10, whereas the same treatment of original particles gave no peaks assigned to band-gap emission, indicating that the SiO2 shell was sufficiently porous for small ionic species such as Cd2+ to penetrate through the shell and that the photoetched US core incorporated in the SiO2 shell had a bare surface to be covered with a cadmium hydroxide layer. With increasing shell thickness, the rate of CdS photoetching was reduced as a result of decrease in the rate of scavenging of the photogenerated electrons in US by electron acceptors such as O-2 and methyl viologen (MV2+) in solution. The structure of the SiO2 layer was varied by surface modification of the US with both 3-mercaptopropionic acid (MPA) and 3-mercaptopropyltrimethoxysilane (MPTS) followed by hydrolysis of its trimethoxysilyl group. FT-IR spectra showed that MPA molecules, but not MPTS molecules, attached to the US core surface were eliminated by photoetching of the particles, resulting in the formation of windows in the SiO2 shell. The behavior of US emission quenching suggested that MV2+ is transported through the windows to the void space inside the SiO2 shell to reach the US core.

Light intensity dependence of the action spectra of photocatalytic reactions with anatase titanium(IV) oxide 査読有り

T. Torimoto, Y. Aburakawa, Y. Kawahara, S. Ikeda, and B. Ohtani

Chem. Phys. Lett. 392 巻 ( 1-3 ) 頁： 220-224 2004年7月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Light intensity dependence of action spectra of photocatalytic reactions was investigated using anatase single-phase titanium(IV) oxide powders as photocatalysts. The action spectra normalized at 350 nm were not changed in methanol dehydrogenation with the range of intensities of ca. 0.1-10 mW cm(-2), while those for acetic acid decomposition were red-shifted with increase in light intensity. The apparent quantum yield of the former was almost independent of the irradiation intensity, but that of the latter was declined with increase in light intensity, the degree being considerably enhanced with the irradiation at shorter wavelength when the light intensity was higher than 2 mW cm-2. These can be explained by the difference in the utilization efficiency of photogenerated charge carriers. (C) 2004 Elsevier B.V. All rights reserved.

半導体ナノ粒子の形状制御と光化学特性招待有り

鳥本　司

光化学 35 巻頁： 42-44 2004年

Preparation of Novel Silica-Cadmium Sulfide Composite Nanoparticles Having Adjustable Void Space by Size-Selective Photoetching, 査読有り

T. Torimoto, J. P. Reyes, K. Iwasaki, B. Pal, T. Shibayama, K. Sugawara, H. Takahashi, and B. Ohtani

J. Am. Chem. Soc. 125 巻頁： 316-317 2003年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

The size-selective photoetching technique was used to control the size of a CdS nanoparticle inside a silica shell. With monochromatic light irradiation, the diffuse reflectance spectra of silica-coated CdS nanoparticles were blue-shifted, and the size of the resulting CdS nanoparticles incorporated in the silica shells was adjustable by varying the wavelength of irradiated light. TEM observation revealed that the original CdS nanoparticle seemed to be in close contact with the amorphous silica shell to leave almost no clearance, while the monochromatic light irradiation caused the decrease in the size of CdS particles, resulting in the formation of a void space between the photoetched CdS core particle and the silica shell. The average void spaces available in the shells were calculated to be ca. 1.4 and 2.4 nm with the irradiation at 514 and 458 nm, respectively. These results indicated that the size-selective photoetching technique enables the regulation of void space formed in the core-shell structure by choosing the wavelength of irradiation light.

Layer-by-Layer Accumulation of Cadmium Sulfide Core-Silica Shell Nanoparticles and Size-Selective Photoetching to Make Adjustable Void Space Between Core and Shell 査読有り

T. Torimoto, J. P. Reyes, S.-y. Murakami, B. Pal, B. Ohtani

J. Photochem. Photobiol. A Chem. 160 巻頁： 69-76 2003年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Layer-by-layer accumulation of monolayers of silica-coated cadmium sulfide (CdS) was achieved through repeated monolayer deposition–hydrolysis cycles using CdS particles (average diameter: 5 nm) modified with 3-mercaptopropyltrimethoxysilane (MPTS) and glass substrates. Absorption spectroscopic analyses of the resulting yellow films revealed that each layer had almost the same thickness, the estimated density of which corresponded to ca. 66% of that for close hexagonal packing of nanoparticles. Monochromatic light
irradiation at 488, 458, or 436 nm onto the film immersed in oxygen-saturated aqueous methylviologen solution caused a decrease in the size of the CdS core depending on the irradiation wavelength, while atomic force microscopic analyses suggested that the size of the silica
shell of the immobilized nanoparticles was almost unchanged by irradiation, i.e., the immobilized silica-coated CdS nanoparticles had void spaces between the photoetched core and the silica shell, and their sizes could be regulated by choosing the wavelength of irradiation light. This size-selective photoetching was applied to nanoparticulate films that had been heat-treated at 473, 573 or 673K to observe the blue-shift of the absorption edge of CdS to the irradiation wavelength. The amount of CdS remaining in the film after the photoetching process depended on the temperature of heat treatment. The largest amount among as-prepared and heat-treated samples was obtained at 473K and decreased with an increase in temperature. The growth of particles, i.e., the diminution of particle number, and/or the diminution
of number of separated independent shells may account for this dependence.

Development of Photocatalytic Reaction System for Oxidative Decomposition of Volatile Organic Compounds in Water with Enhanced Aeration 査読有り

R. Villacres, S. Ikeda, T. Torimoto, B. Ohtani

J. Photochem. Photobiol. A:Chem. 160 巻頁： 121-126 2003年

記述言語：英語掲載種別：研究論文（学術雑誌）

A novel photocatalytic reaction system, composed of solution and gas spaces that are divided by a thin Teflon film and titanium(IV) oxide (TiO2)-coated mesh or cloth, for the treatment of contaminated aqueous solutions was developed to be operated with enhanced aeration without bubbling of air in the solution. First, the photocatalytic activities of TiO2 particles immobilized on two kinds of support material, stainless steel mesh (SSM) and fiberglass cloth (FGC), were investigated for photocatalytic oxidation of 2-propanol, as a model
volatile organic compound, dissolved in aerated aqueous solution. The TiO2 particles immobilized on both support materials exhibited photocatalytic activity to oxidize 2-propanol into acetone and carbon dioxide (CO2), and the activity levels of the TiO2 particles immobilized
on the two kinds of support materials were comparable. Presumably due to the presence of a small amount of metal species originating in SSM that might work as reduction catalysts, molecular hydrogen (H2) was also liberated on the TiO2-immobilized SSM. Results of analysis of weight loss after photoirradiation suggested that the stability of the TiO2-immobilized FGC was better than that of the
TiO2-immobilized SSM. On the basis of these results, FGC was employed in construction of a photocatalytic reactor equipped with an oxygen (O2)-permeable Teflon membrane in order to make oxygen pass from a gas space to a solution space and to keep the surface of the immobilized TiO2 photocatalyst, facing an aqueous solution containing volatile organic compounds, saturated with dissolved O2. From the results of photocatalytic oxidative decomposition of 2-propanol, it was clarified that the surfaces of TiO2 particles could be sufficiently supplied with O2 from the gas space through the membrane to accelerate the oxidation.

Photochemical Hydrogen Evolution from Aqueous Triethanolamine Solutions Sensitized by Binaphthol-Modified Titanium(IV) Oxide under Visible Light Irradiation 査読有り

S. Ikeda, C. Abe, T. Torimoto, B. Ohtani

J. Photochem. Photobiol. A: Chem. 160 巻頁： 61-67 2003年

記述言語：英語掲載種別：研究論文（学術雑誌）

Surface modification of titanium(IV) oxide (TiO2) powders with 1,1-binaphthalene-2,2-diol (bn(OH)2), having two phenolic hydroxyls and atropisomeric chirality, in refluxed ethanol led to the formation of a deep yellow-colored surface complex, giving visible-light absorption
at a wavelength below ca. 550–600 nm. Quantitative analyses of the surface complex revealed that absorption intensity at 450 nm in diffuse reflection (DR) measurement was almost proportional to its amount and that its amount depended strongly on the amount of surface hydroxyl groups of TiO2 but not on the crystal structure of TiO2, anatase, and rutile. The bn(OH)2 complexation was also applied to
platinized TiO2 to drive photocatalytic molecular hydrogen (H2) evolution from deaerated triethanolamine solutions under visible-light irradiation at a wavelength even longer than 540 nm. The photonic efficiency of the photocatalytic reaction at 450 nm was estimated to be
0.02% for bn(OH)2-modified TiO2 (JRC-TIO-3) loaded with 0.1 wt.% of platinum. On the basis of these experimental results, the reaction mechanism, which involves visible-light excitation of the surface complex, injection of electrons from the complex to TiO2, and migration
of the electrons to platinum deposits, where reduction of H+ takes place to give H2, was elucidated.

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