| Research Abstract |
The dynamic behaviors of radicals and radical ions generated on the surface of TiO_2 photocatalyst and the reactive intermediates from the reactions of the radicals and radical ions has been studied to elucidate 1) the reactive oxygen species and organic reactive intermediates generated during the TiO_2 photocatalytic reactions and 2) reactivities of organic radical ions generated during TiO_2 photocatalytic reactions, and to develop the method for the measurement of charge separation on the surface of the TiO_2 photocatalyst. There is an application to the environmental cleanup (contaminant processing) and medical technology as application of the TiO_2 photocatalyst reaction. An important finding was especially obtained in relation to it for the decomposition mechansm of the organic compounds in the TiO_2 photocatalyst reaction. In 2001-2005 fiscal years, we studied that adsorption and one-electron oxidation reaction process of the substrate adsorbed on the TiO_2 surface based on the
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time-resolved transient reflection measurement, and found that one-election oxidation efficiency depends on not only the oxidation potential of the substrate but also the electronic interaction between the substrate and surface of TiO_2 remarkably. In 2005-2007 fiscal years, we studied visible-light responsible TiO_2 photocatalyst, TiO_2 photocatalytic reaction in gas phase, one-electron redox processes during the polyoxometalate-mediated TiO_2 photocatalytic reactions, one-electron oxidation of organic molecule included in the cavity of β-cyclodextrin modified TiO_2 photocatalyst, and non-contact TiO_2 photocatalytic reaction based on the transient absorption measurement and single molecule fluorescence imaging technique. We found that the hydroxy radical and the singlet oxygen were generated from the surface of TiO_2 by the light irradiation of the TiO_2 photocatalyst and diffuse in 120 micrometer and 2 millimeter, respectively, in the atmosphere. We also studied nanoscopic heterogeneities in ddsorption and electron transfer processes of perylene diimide dye on TiO_2 nanoparticles, real-time single-molecule imaging of the spatial and temporal distribution of reactive oxygen species, and photocatalytic cleavage of single TiO_2/DNA nanoconjugates, as relation to solar cell, TiO_2 photocatalytic reaction mechanism at single molecule level, and DNA conjugate of TiO_2 photocatalyst.. In conclusion, our results can initiate to develop new TiO_2 photocatalyst and and the TiO_2 photocatalyst reaction system with a greatly highly efficiency and high selectivities. Less
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