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Tomoki Akita

Publications and source records attributed to Tomoki Akita.

12 recordsLinked to original sources
PubMed2006

All-solid-state Z-scheme in CdS-Au-TiO2 three-component nanojunction system.

Natural photosynthesis, which achieves efficient solar energy conversion through the combined actions of many types of molecules ingeniously arranged in a nanospace, highlights the importance of a technique for site-selective coupling of different materials to realize artificial high-efficiency devices. In view of increasingly serious energy and environmental problems, semiconductor-based artificial photosynthetic systems consisting of isolated photochemical system 1 (PS1), PS2 and the electron-transfer system have recently been developed. However, the direct coupling of the components is crucial for retarding back reactions to increase the reaction efficiency. Here, we report a simple technique for forming an anisotropic CdS-Au-TiO2 nanojunction, in which PS1(CdS), PS2(TiO2) and the electron-transfer system (Au) are spatially fixed. This three-component system exhibits a high photocatalytic activity, far exceeding those of the single- and two-component systems, as a result of vectorial electron transfer driven by the two-step excitation of TiO2 and CdS.

Journal Article↗
PubMed2006

Synthesis of small palladium nanoparticles stabilized by bisphosphine BINAP bearing an alkyl chain and their palladium nanoparticle-catalyzed carbon-carbon coupling reactions under room-temperature.

A new bisphosphine ligand, C8-BINAP, and C8-BINAP-stabilized palladium nanoparticles have been prepared; C8-BINAP was found to be an effective protecting ligand for preparing and stabilizing palladium nanoparticles with very small core size and narrow size distribution and the C8-BINAP-Pd nanoparticles behave as an efficient catalyst for carbon-carbon coupling reactions at room temperature.

Journal Article↗
PubMed2005

Platinum dissolution and deposition in the polymer electrolyte membrane of a PEM fuel cell as studied by potential cycling.

The behavior of platinum dissolution and deposition in the polymer electrolyte membrane of a membrane-electrode-assembly (MEA) for a proton-exchange membrane fuel cell (PEMFC) was studied using potential cycling experiment and high-resolution transmission electron microscopy (HRTEM). The electrochemically active surface area decreased depending on the cycle number and the upper potential limit. Platinum deposition was observed in the polymer electrolyte membrane near a cathode catalyst layer. Platinum deposition was accelerated by the presence of hydrogen transported through the membrane from an anode compartment. Platinum was transported across the membrane and deposited on the anode layer in the absence of hydrogen in the anode compartment. This deposition was also affected by the presence of oxygen in the cathode compartment.

Chemical Phenomena↗
PubMed2005

Kinetic and DFT studies on the Ag/TiO2-photocatalyzed selective reduction of nitrobenzene to aniline.

TiO2 particles loaded with silver nanoparticles with a mean diameter of 1.5 nm exhibit a high photocatalytic activity (84 % conversion after 1 h irradiation) for the reduction of nitrobenzene to aniline with 100 % selectivity in the presence of CH3OH (concentration=100 mM). High-resolution transmission electron microscopic studies of Pt-photodeposited Ag/TiO2 demonstrate that the Ag nanoparticles act as reduction sites in the photocatalytic reaction. Both spectroscopic measurements and density functional theory (DFT) calculations reveal that nitrobenzene is selectively adsorbed onto the Ag surfaces of Ag/TiO2 via partial electron transfer from Ag to nitrobenzene, whereas the interaction between aniline and Ag/TiO2 is weak. The kinetic analysis indicates that the recombination between the electrons flowing into the Ag nanoparticle and the holes left in the TiO2 valence band is significantly suppressed, particularly in the presence of CH3OH. The high activity and selectivity in the present Ag/TiO2-photocatalyzed reduction are rationalized in terms of the charge separation efficiency, the selective adsorption of the reactants on the catalyst surfaces, and the restriction of the product readsorption.

Aniline Compounds↗
PubMed2005

Low-temperature synthesis of anatase-brookite composite nanocrystals: the junction effect on photocatalytic activity.

Anatase-brookite composite nanocrystals have successfully been synthesized at 50 degrees C using a simple liquid-phase process. The photocatalytic activity of the sample for the gas-phase oxidation of CH3CHO is 5.4 times greater than that of a single-phase anatase sample with comparable crystallite size and surface area. Electron energy loss spectra suggest that this high activity results from junction between anatase and brookite crystals.

Letter↗
PubMed2005

TEM observations of Au and Ir particles supported on CeO2.

Au/CeO2 and Ir/CeO2 catalysts were observed by a transmission electron microscope in order to investigate the nano-structures of Au and Ir particles and CeO2 grains and the interface structure between metallic particles and CeO2. An annular dark field scanning transmission electron microscope (ADF-STEM) and an energy dispersive X-ray spectroscopy (EDS) revealed that the metallic particles smaller than 2 nm in diameter are highly dispersed on CeO2 supports in both catalysts. For model samples of larger CeO2 particles with flat facets of low-index surfaces, high resolution transmission electron microscopy observations of Au/CeO2 and Ir/CeO2 interfaces were made and the epitaxial relationship between Au and CeO2, (111)[110]Au//(111)[110]CeO2 has been found for the first time.

Journal Article↗
PubMed2004

Structural analyses by TEM of iridium deposited on TiO2 powder and rutile single crystal.

It was found by transmission electron microscopy (TEM) that deposition precipitation of Ir onto TiO2 powder (Degussa P-25) produced Ir particles preferentially on the rutile phase. Iridium oxide particles supported on rutile TiO2 single crystal by deposition precipitation were also observed by TEM and scanning electron microscopy, and were found to exist as thin films of a few atoms. A structural change caused by hydrogen reduction was observed using high-resolution TEM and this was confirmed to be the iridium oxide film being reduced to metallic iridium particles.

Crystallization↗
PubMed2003

Electron holographic 3-D nano-analysis of Au/TiO2 catalyst at interface.

Three-dimensional (3-D) nanostructures of gold catalysts supported on TiO2 were analysed by electron holography and high-resolution electron microscopy. The contact angle of the gold particle on TiO2 tended to be >90 degrees in the case of gold particles with a size (height) of >4 nm and it tended to be <90 degrees for gold particles with a height of <2 nm. The change in morphology increases the perimeter at the Au/TiO2 interface as the particle size decreases. This change in 3-D structure should be attributed to a change in electronic structure at the interface. It was found that electron holography enabled 3-D analysis at the atomic level and was effective for analysing nanostructured particles.

Journal Article↗
PubMed2003

Analytical TEM observation of Au and Ir deposited on rutile TiO2.

As a model catalyst, gold and iridium were co-deposited on a single crystal of rutile TiO2 using the deposition precipitation method in order to clarify the synergetic effect of the combination of Au with Ir on the catalytic performance of the oxidative decomposition of odour and dioxins. Analyses by means of high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy and electron energy-loss spectroscopy revealed that pillars of IrO2 grew on the TiO2 substrate to each of which one Au nanoparticle was attached. This mushroom-like structure appeared to be formed by self-organization of Au, Ir and oxygen. Epitaxial contact was observed between the Au nanoparticle/IrO2 pillar and IrO2 pillar/TiO2 substrate interfaces. The growth process of the structure was investigated by transmission electron microscope observations of the Au-Ir complex before and after heating in air.

Crystallization↗