Showing papers by "Masaya Matsuoka published in 2008"

The Effect of Chemical Etching by HF Solution on the Photocatalytic Activity of Visible Light-responsive TiO 2 Thin Films for Solar Water Splitting

Abstract: The effect of chemical etching by HF solution on the photoelectrochemical performance and photocatalytic activity of visible light-responsive TiO2 (Vis-TiO2) thin films prepared by a radio-frequency magnetron sputtering method has been investigated. It was found that Vis-TiO2 thin films treated with HF solution (HF-Vis-TiO2) exhibit a remarkable enhancement of the photoelectrochemical performance not only under UV but also visible light irradiation as compared to untreated Vis-TiO2. The incident photon to current conversion efficiencies reached 66 and 9.4% under UV (λ = 360 nm) and visible light (λ = 420 nm), respectively. The HF-Vis-TiO2 thin films have a larger surface area and higher donor density than Vis-TiO2, indicating that the remarkable increase in the photocurrent may be due to the short diffusion length of the photoformed holes in reaching the solid–liquid interface as well as to the high conductivity. Moreover, the HF-Vis-TiO2 thin films were found to act as efficient photocatalysts for the decomposition of water with the separate evolution of H2 and O2 from H2O under visible or sunlight irradiation.

Enhancement of the Photocatalytic Activity Under Visible-Light Irradiation over N-doped TiO2 Modified by Platinum Chloride

Abstract: N-doped TiO2 adsorbed platinum chloride (PtCl x /N-TiO2, x being an unidentified number) was found to show much higher photocatalytic activity than either N-TiO2 or PtCl x /TiO2 for the decomposition of acetic acid into CO2 and H2O under Visible-light irradiation, while neither PtCl x /SiO2, PtCl x /Al2O3 nor an aqueous solution of H2PtCl6 was active. An enhancement of the photo-activity on PtCl x /N-TiO2 has been proposed as a Z-scheme mechanism.

Structural evaluation and photocatalytic properties of Pt-supported titanate nanotubes

Abstract: Pt nanocrystal-supported titanate nanotubes as a photocatalyst were prepared by hydrothermal treatment and subsequent heat-treatment in H2 atmosphere (H2 reduction) of a mixture of these titanate nanotubes and H2PtCl6. TEM results showed that Pt nanoparticles (a few nm in diameter and 5 to 10 nm in length) with good crystallinity were entrapped inside titanate naotubes and were closely precipitated on the surface of titanate nanotubes. These Pt nanocrystal-supported titanate nanotubes possessed the high ability for HCHO decomposition.

Synthesis of the Ag+-Bipyridine Complexes Anchored within MCM-41 and their Photocatalytic Reactivity for N2O Reduction with CO

Abstract: Bipyridine derivatives were covalently anchored on the surface of the mesopores of MCM-41 porous material and the further introduction of Ag+ ions led to the formation of Ag+ bipyridine complexes by the chelation of the Ag+ ions with the bipyridine units. The successful covalent immobilization of the bipyridine derivatives as well as the Ag+ bipyridine complexes has been confirmed by various spectroscopic investigations such as FT-IR, UV-vis, and XPS analyses. It was found that the anchored bipyridine derivatives on the surface of MCM-41 prevent the reduction and agglomeration of the Ag+ species even after evacuation treatment at 573 K. Thus, the anchored Ag+ ions chelated with the bipyridine units inside the mesopores of MCM-41 were observed to exhibit photocatalytic reactivity for N2O reduction with CO.

Effect of HF treatment on the activity of TiO2 thin films for photocatalytic water splitting

Abstract: The effects of HF treatment on the activity of TiO2 thin films for the photocatalytic water splitting reaction have been investigated. TiO2 thin films treated with HF solution (HF-TiO2) were found to exhibit a remarkable enhancement of the photocatalytic activity for H2 evolution from a methanol aqueous solution, as well as efficient photoelectrochemical performance under UV light irradiation as compared with the untreated TiO2. Moreover, Pt-loaded HF-TiO2 thin films were found to act as efficient and stable photocatalysts for the decomposition of water under UV light irradiation. The mechanistic insights obtained in the present study will be useful in the design of highly efficient photocatalysts for the decomposition of water.

Photocatalytic selective oxidation of CO with O2 in the presence of H2 over highly dispersed chromium oxide on silica under visible or solar light irradiation

Abstract: A highly dispersed Cr6+-oxide species on silica (Cr/SiO2) was found to act as an efficient photocatalyst for the selective oxidation of CO into CO2 with O2 in the presence of H2 under visible (λ>420 nm) or solar light irradiation at 293 K. UV-Vis, photoluminescence and FT-IR investigations revealed that the selective reactivity of the photoexcited tetrahedral Cr6+-oxide species ([Cr5+−O−]*) with CO, as well as the high reactivity of the photoreduced Cr6+-oxide species (Cr4+-oxide species) with O2 both play significant roles in this reaction.

Photoluminescence Spectroscopy and Its Application to the Characterization of Active Sites and Reaction Dynamics in Catalysis

Abstract: The sections in this article are Introduction Characterization of Catalysts by Photoluminescence and Time-Resolved Photoluminescence Spectroscopy Investigations of the Dynamics of Photocatalysis by Time-Resolved Photoluminescence Spectroscopy Conclusions Keywords: photoluminescence, time resolved spectroscopy, photocatalysis, active sites

Photocatalytic Decomposition of Lactic Acid in Water on a Photoelectrochemical Circuit System Consisting of a Rod-type TiO2 Electrode and Silicon Solar Cell

Abstract: Lactic acid, a well-known substance causing dental caries, was dissolved in water and completely oxidized into CO2 and H2O on a powdered TiO2 photocatalyst under UV light irradiation. Furthermore, a unique photoelectrochemical circuit system consisting of a rod-type TiO2 electrode and counter electrode connected through a silicon solar cell was constructed and its photocatalytic activity for the decomposition of lactic acid was investigated. The photoelectrochemical circuit system was found to effectively mineralize the lactic acid in water into CO2 while the negative bias applied on the rod-type TiO2 electrode enhanced the photocatalytic decomposition rate of the lactic acid.

Photocatalytic decomposition of N 2O in the presence of CO on Ti/USY photocatalysts

Abstract: A highly dispersed Ti-oxide species was prepared within an ultra stable Y-zeolite (USY zeolite) by an impregnation method. Moreover, the Ti-oxide loaded USY (Ti/USY) zeolite showed higher photocatalytic activity for the decomposition of N 2O in the presence of CO to produce N 2 and CO 2 than the standard TiO 2 (P-25) photocatalyst at 298 K. The photocatalytic reaction rate was found to strongly depend on the Ti loadings of Ti/USY. XRD, XANES, UV-vis and photoluminescence investigations revealed that this highly dispersed Ti-oxide species plays an important role as the active sites in the photocatalytic decomposition of NO in the presence of CO.

Photocatalysis: Development of Highly Functional Titanium Oxide Photocatalysts

Abstract: The sections in this article are Introduction Ion Engineering Techniques for the Preparation of Well-Defined TiO2 Photocatalysts Visible Light-Responsive TiO2 Photocatalysts Modification of the Electronic Properties of TiO2 Semiconducting Fine Powder Photocatalysts by an Advanced Metal Ion Implantation Method Preparation of Highly Transparent TiO2 Thin-Film Photocatalysts Preparation of Visible Light-Responsive TiO2 Thin-Film Photocatalysts by RF-Magnetron Sputtering (RF-MS) Deposition in a Single Process Photo-induced Superhydrophilic Properties on the Surface of the TiO2 Thin-Film Photocatalysts Conclusions Keywords: photocatalysis; titanium oxide photocatalysts