Showing papers by "Akira Fujishima published in 2013"

Broad Spectrum Microbicidal Activity of Photocatalysis by TiO2

Abstract: Photocatalytically active titanium dioxide (TiO2) is widely used as a self-cleaning and self-disinfecting material in many applications to keep environments biologically clean. Several studies on the inactivation of bacteria and viruses by photocatalytic reactions have also been reported; however, only few studies evaluated the spectrum of the microbicidal activity with photocatalysis for various species. There is a need to confirm the expected effectiveness of disinfection by photocatalysis against multidrug-resistant bacteria and viruses. In this study, microbicidal activity of photocatalysis was evaluated by comparing the inactivation of various species of bacteria and viruses when their suspensions were dropped on the surface of TiO2-coated glass. Gram-positive bacteria, e.g., methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecalis, and penicillin-resistant Streptococcus pneumoniae, were easily inactivated by photocatalysis, whereas some gram-negative bacteria, e.g., Escherichia coli and multidrug-resistant Pseudomonas aeruginosa, were gradually inactivated by photocatalysis. Influenza virus, an enveloped virus, was significantly inactivated by photocatalysis compared with feline calicivirus, a non-enveloped virus. The effectiveness of microbicidal activity by photocatalysis may depend on the surface structure. However, they are effectively inactivated by photocatalysis on the surface of TiO2-coated glass. Our data emphasize that effective cleaning and disinfection by photocatalysis in nosocomial settings prevents pathogen transmission.

Factors Affecting UV-Induced Superhydrophilic Conversion of a TiO2 Surface

Abstract: The present study explored the effects of several factors (wetting, light intensity, spectral variation of the actinic light, heating, and surface acidity) on the hydrophilic conversion of the surface of TiO2 nanocoatings. The experimental dependencies of the efficiencies of photoinduced hydrophilic surface conversion on the intensity and wavelength of the actinic light clearly indicate the role of electronic photoexcitation in hydrophilic surface transformation. Particularly, the maximum extrema in spectral dependence of the efficiency of photoinduced hydrophilic conversion correspond to the energies of the first indirect and first direct electronic band-to-band transitions in TiO2. At the same time, temperature dependence and the effect of the surface acidity on the hydrophilic behavior of the TiO2 surface demonstrate the importance of the multilayer hydrate structure in both the original hydrophilicity of the surface and the direction of the photoinduced hydrophilic conversion. Estimation of the surfac...

Cosensitization Properties of Glutathione-Protected Au25 Cluster on Ruthenium Dye-Sensitized TiO2 Photoelectrode

Abstract: Cosensitization by glutathione-protected Au25 clusters on Ru complex, N719-sensitized TiO2 photoelectrodes is demonstrated. Glutathione-protected Au25 clusters showed no significant changes in properties after adsorption onto TiO2 particles, as confirmed by optical absorption spectroscopy, transmission electron microscopy, and laser desorption/ionization mass spectrometry. Adsorption property of the glutathione-protected Au25 clusters depends on the pH, which affects the incident photon-to-current conversion efficiency (IPCE) of the TiO2 photoelectrode containing Au25 clusters. When pH 7. The IPCE of a TiO2 photoelectrode sensitized by both glutathione-protected Au25 clusters and N719 was increased compared with photoelectrodes containing either glutathione-protected Au25 clusters or N719, which suggests that glutathione-protected Au25 clusters act as a coadsorbent for N719 on TiO2 photoelectrodes. This is also supported by the results that the IPCE of N719-sensitized TiO2 photoelectrodes increased upon addition of glutathione. Furthermore, cosensitization by glutathione-protected Au25 clusters on N719-sensitized TiO2 photoelectrodes allows that wavelength of photoelectric conversion was extended to the near infrared (NIR) region. These results suggest that glutathione-protected Au25 clusters act not only as a coadsorbent to increase IPCE but also as an NIR-active sensitizer.

Recent Aspects of Photocatalytic Technologies for Solar Fuels, Self-Cleaning, and Environmental Cleanup

Abstract: Increasingly severe climatic, energy, and environmental problems warrant the need to continue to develop greenhouse gas-mitigating, energy-producing, energysaving, environmentally-beneficial technologies. The closely related fields of semiconductor photoelectrochemistry and semiconductor photocatalysis, largely involving titanium dioxide, have blossomed during the past forty years since the publication of our initial work on photoelectrochemical water splitting.1 This highly cited paper has provided a foundation for steadily increasing numbers of works on a broad range of topics, including applications such as solar light-induced water splitting (hydrogen production)2, CO2 reduction to produce carbonaceous solar fuels,3 water purification, decontamination, and disinfection, as well as new materials and fundamental aspects. Our recent review summarizes a number of photocatalytic applications, including selfcleaning surfaces, anti-fogging surfaces, heat dissipation, corrosion prevention, and visible light-sensitive materials.4 Figure 1 illustrates such a broad range of applications. The topics of “designer” titanium dioxide materials with various levels of dimensionality5,6 and photocatalysis for environmental applications7 have also been investigated thoroughly in our laboratory. Our early work on photocatalytic3 and photoelectrochemical8,9 CO2 reduction is now continuing at present, in the laboratory of our colleague, Akihiko Kudo,10 and in our own laboratory, both at the Tokyo University of Science, as well as by a number of other groups around the world. At the outset, we would like to emphasize the essential unifying principles of photocatalysis before presenting some specific examples. After energetic photons are absorbed in the semiconductor, electrons and holes are generated. The mobile electrons are free to move around, reaching the surface of the solid, and then react with water or oxygen. Similarly, the mobile, highly energetic holes reach the surface and oxidize water and/or organic matter. Thus, there are four simple cases for reactions involving the electrons and holes: (Case 1) water-water, (Case 2) oxygenwater, (Case 3) water-organic, and (Case 4) oxygen-organic. Cases 3, 4, and 5 are all involved with photocatalytic decomposition of organics, whereas Case 1 is likely to be involved in the photoinduced hydrophilic effect (PIHE), as well as photocatalytic water splitting. Fig. 1. Overview of photocatalytic applications.