Showing papers by "Akira Fujishima published in 1998"

Effect of Ultrasonic Treatment on Highly Hydrophilic TiO2 Surfaces

Abstract: Glass surfaces coated with polycrystalline titanium dioxide (TiO2) films were found to exhibit a 0° water contact angle when the surfaces were illuminated with UV light in the air. This highly hydrophilic surface was maintained for more than 1 week in the dark in air. However, ultrasonic treatment in pure water decreased the degree of surface hydrophilicity, yielding a contact angle of approximately 11°. X-ray photoelectron spectroscopic measurements indicated that hydroxyl groups and molecular water adsorption, which govern the surface wettability, were partially removed from the surface by the ultrasonic treatment. The effect of ultrasonic treatment was ascribed to the generation of OH radicals that reoxidized the photoreduced surface, accompanied by the removal of surface-adsorbed water. This has been confirmed by adding acrylamide, a typical OH radical scavenger, to pure water to effectively suppress the hydrophilic-to-hydrophobic reconversion on the TiO2 surface.

Photocatalytic Degradation of Gaseous Formaldehyde Using TiO2 Film

Abstract: The photocatalytic degradation of gaseous formaldehydea major cause of sick building syndromewas studied using a TiO2 thin film. TiO2 thin films have many unique photoinduced properties, for example, self-cleaning, anti-fouling, and anti-bacterial functions. UV illumination of the TiO2 thin film placed in a gaseous formaldehyde/air environment resulted in the total mineralization of formaldehyde to CO2 and H2O. We invoked a Langmuir−Hinshelwood kinetic model to analyze the dependence of reaction rates on the concentration of formaldehyde. In addition, the overall decomposition rate constant for formaldehyde was comparable to that of acetaldehyde (a standard test reactant) for initial concentrations of up to 1000 ppmv. However, the apparent adsorption constant Kapp of formaldehyde onto TiO2 was ca. 2.5 times larger than that of acetaldehyde. Thus in the low concentration regime, the reactivity of formaldehyde appeared to be greater than that of acetaldehyde. In like manner, a dark adsorption experiment als...

Autoxidation of Acetaldehyde Initiated by TiO2 Photocatalysis under Weak UV Illumination

Abstract: The photocatalytic decomposition efficiency of gas-phase acetaldehyde was studied using a titanium dioxide thin film under weak UV illumination. Acetic acid and carbon dioxide were detected as the main reaction products. It was found that the apparent quantum yields (QY) for acetaldehyde degradation are determined by the normalized absorbed photon number (Inorm /s-1), a parameter that is defined as the ratio of the number of absorbed photons to the number of adsorbed acetaldehyde molecules. This result is similar to that for 2-propanol degradation reported previously (Ohko, Y.; Hashimoto, K.; Fujishima, A. J. Phys. Chem. A 1997, 101, 8057). However, although the QY values for 2-propanol degradation reached a constant value (ca. 28%) for very low relative light intensity (in the Inorm region less than 10-4 s-1), those for acetaldehyde degradation continued to increase with decreasing Inorm and reached 180% for an initial concentration of 1000 ppmv, at an Inorm value of 3 × 10-5 s-1. This discrepancy is due...

New Mesostructured Porous TiO2 Surface Prepared Using a Two-Dimensional Array-Based Template of Silica Particles

Abstract: Mesoporous photocatalytic titanium dioxide films with periodic structures were prepared by molding from two-dimensionally ordered arrays of monodisperse SiO2 particles. The morphology of the porous structures in these films was dependent upon the annealing temperature. The photocatalytic activity of the films was confirmed, as evidenced by the photodeposition of silver on the textured film surfaces. Attachment of the free-standing films to rigid supports allowed us to locate specific microscopic areas at will and to monitor the progress of the silver photodeposition in these areas using optical microscopy and scanning electron microscopy, with both secondary electron and backscattered electron detection. However, the repeated electron beam exposure in these selected areas was found to adversely affect the photoreducibility. Although the detailed film morphology did not affect the macroscopic photocatalytic activity, we found subtle differences in the silver nucleation process which depended upon the pore ...

Photoelectrochemical reduction of co2 in a high-pressure co2 + methanol medium at p-type semiconductor electrodes

Abstract: Photoelectrochemical CO2 reduction was examined in a high-pressure (40 atm) CO2 + methanol medium using the p-type semiconductor electrodes p-InP, p-GaAs, and p-Si. With the p-InP photocathodes, current densities up to 200 mA cm-2 were achieved, with current efficiencies of over 90% for CO production, while hydrogen gas evolution was suppressed to low levels. At high current densities and CO2 pressures, the CO2 reduction current was found to be limited principally by light intensity. Of the various factors that were found to influence the product distribution, including the concentrations of added water and strong acid, CO2 pressure was the most critical factor. We propose that the adsorbed (CO2)2•- radical anion complex reaches high coverages at high CO2 pressures and is responsible for both the high current efficiencies observed for CO production and the low values observed for H2 evolution. Furthermore, we propose that this adsorbed complex is responsible for stabilizing all three semiconductor electro...

Surface Functionalization of Doped CVD Diamond via Covalent Bond. An XPS Study on the Formation of Surface-bound Quaternary Pyridinium Salt

Abstract: Lightly boron-doped polycrystalline diamond thin films prepared on single crystal silicon wafers via chemical vapor deposition (CVD) were treated with chlorine (Cl2) under ultraviolet (> 200 nm) photoirradiation and then heated in boiling pyridine. Ex situ X-ray photoelectron spectroscopic measurements suggested the plausible formation of surface-bound chloride species and quaternary pyridinium salt by these chemical processes.

Adhesion Mechanism of Electroless Copper Film Formed on Ceramic Substrates Using ZnO Thin Film as an Intermediate Layer

Abstract: Electroless Cu layers with pull strengths of greater then 2.5 kg/mm 2 were fabricated on smooth ceramic substrates (glass, Al 2 O 3 , AlN) without surface etching (R a ≤ 0.05 μm). High adherence was achieved using ZnO thin films (ca. 1 μm thickness), prepared by spray pyrolysis as an intermediate layer between the ceramic substrates and the Cu layers. It was shown from the interfacial analysis that the high adherence was due to both strong van der Waals forces acting at the Cu/ZnO interface and a chemical-type bond acting at the ZnO/ceramic interface. The adhesive forces at the Cu/ZnO interface were enhanced by numerous small pores <0.5 μm diam) formed on the ZnO thin film during catalyzation. In contrast, the ZnO/ceramic adhesion was due to the thermal diffusion of Zn into the substrate during the preparation of the ZnO thin film, which involves chemical bonding forces. As a result, the ZnO thin film acts as a highly effective adhesive layer between the electroless Cu layer and the ceramic substrate.

Observation of Electrochemical C60 Reduction of a Diamond Thin Film Electrode at Room Temperature

Abstract: Highly conductive boron-doped diamond thin film electrodes were used for the first time to examine the cyclic voltammetric behavior of C60 reduction at room temperature as a demonstration of the relatively wide potential window in nonaqueous media. Five reduction peaks were observable on diamond electrodes at room temperature, while four reduction peaks were observed on Pt.

Photoelectrochemical Reduction of CO 2 at High Current Densities at p‐InP Electrodes

Abstract: High-rate cathodic photoelectrolysis of CO{sub 2} was conducted in a high pressure CO{sub 2} + methanol medium at p-InP electrodes. Current densities up to 100 mA/cm{sup 2} were achieved, with current efficiencies up to 93% for CO production. The photoelectrochemical reduction of CO{sub 2} in the highly concentrated CO{sub 2}-methanol solution was limited at the higher current densities (50--100 mA/cm{sup 2}) by light intensity and not by the mass transport of CO{sub 2}.

Electrochemical Reduction of CO2in Micropores

Abstract: CO2 electroreduction was examined on high area nickel electrocatalysts supported on activated carbon fibers, which contain slit-shaped pores with widths on the order of nanometers. The current efficiency for CO2 reduction to CO reached values of 70%. In contrast, much smaller amounts of CO were generated for the same type of high area nickel catalyst supported on non-activated carbon fibers. The enhancement of the CO2 reduction selectivity with the microporous support is thought to include a nanospace effect, which gives rise to high pressure-like effects at ambient pressure.

Surface-Enhanced Raman Imaging (SERI) of Patterned Self-Assembled Monolayers of Various Derivatized Thiophenols on Silver

Abstract: Surface-enhanced Raman imaging (SERI) has recently been developed in our laboratory as an imaging technique which is chemically selective, has monolayer sensitivity, and can be used under ambient conditions. A particularly interesting application of this technique is to image patterned self-assembled monolayers (SAMs). In the present work, we have used both photopatterning and microcontact printing techniques for preparing patterned SAMs with several different terminal functional groups (NO2, OH, COOH, and CH3) on evaporated silver films and have imaged them using SERI. The intrinsic subsurface roughness of the film provides sufficient enhancement for the imaging.

Photoelectrochemical reduction of highly concentrated CO2 in methanol solution

Abstract: High-rate photoelectrolysis of CO 2 was conducted in a high pressure CO 2 + methanol medium using p-type semiconductor electrodes. Current densities of up to 100 mA cm -2 were achieved, with current efficiencies of up to 93 % for CO production on a p-InP photocathode. The effect of CO 2 pressure on the product distributions was examined for p-InP and p-GaAs.

Electrochemical Reduction of CO2 in Micropores

Abstract: CO2 electroreduction was examined on high area nickel electrocatalysts supported on activated carbon fibers, which contain slit-shaped pores with widths on the order of nanometers. The current efficiency for CO2 reduction to CO reached values of 70%. In contrast, much smaller amounts of CO were generated for the same type of high area nickel catalyst supported on non-activated carbon fibers. The enhancement of the CO2 reduction selectivity with the microporous support is thought to include a nanospace effect, which gives rise to high pressure-like effects at ambient pressure.

Activity, and Hardness of Supported TiO2 Films on Pyrex and Soda-Lime Glass in Photocatalytic Degradation of Formic Acid for 50 Days

Abstract: Abstract Photocatalytic degradation of formic acid (HCOOH) in solution was monitored using titanium dioxide (TiO2) films supported on Pyrex and soda-lime glasses (SLG) calcined with two different calcination methods: programmed and short time (10 min) with temperature 100 and 700 °C for both methods. As the calcination temperature and duration increased, the photocatalytic activities using TiO2 films supported on SLG decreased, whereas the photocatalytic activities of TiO2 films supported on Pyrex were not much affected by calcination temperature and duration. TiO2 films supported on both Pyrex and SLG showed reduced photocatalytic activities after -50 days.

Electrochemical Reactions of Organic Materials on Diamond Electrodes

Abstract: The electrochemistry of diamond has gained much importance due to its stability, low background current and wide potential window in aqueous electrolytes. We have used high quality diamond films both from fundamental and applied viewpoints. The detection of biologically important compounds such as dopamine was found to be possible at very low concentrations even in the presence of ascorbic acid, which interferes frequently in biological systems. Similarly, oxidation of nicotinamide dinucleotide (NADH) was observed, with a well defined cyclic voltammogram even in the micromolar range. The electrochemical reduction of C60 at diamond electrode was studied in acetonitrile-toluene mixture, and six reduction peaks were observed at room temperature.