Hiroki Tanaka

Bio: Hiroki Tanaka is an academic researcher. The author has contributed to research in topics: Equilibrium constant & Radical. The author has an hindex of 2, co-authored 2 publications receiving 1020 citations.

Heterogeneous Photocatalytic Decomposition of Phenol over TiO2 Powder

Abstract: The photocatalytic decomposition of phenol in oxygenated aqueous suspensions of lightly-reduced anatase TiO2, being the most satisfactory among the semiconductors investigated from the standpoint of the photocatalytic activity and stability, has been investigated at the optimum pH 3.5. The products at the initial stage of the reaction were hydroquinone, pyrocatechol, 1,2,4-benzenetriol, pyrogallol, and 2-hydroxy-1,4-benzoquinone. These intermediates underwent further photocatalytic oxidation via acids and/or aldehydes finally into CO2 and H2O. A reaction scheme involving hydroxyl radicals as real reactive species has been proposed. Although H2O2 was formed via O2\ewdot produced by electron trapping of adsorbed oxygen, its concentration remained constant at a low value during the reaction. About 0.7 mole of O2 was consumed for the consumption of one mole of phenol at the initial stage of the reaction. These results indicated that hydroxyl radicals were formed not only via holes but also via H2O2 from O2\ew...

Kinetics of Heterogeneous Photocatalytic Decomposition of Phenol over Anatase TiO2 Powder

Abstract: The photocatalytic decomposition of phenol over anatase TiO2 powder followed the first-order kinetics, upto high conversions, of which the apparent rate constant kap depended on initial concentration of phenol [phenol]0, [TiO2], O2 pressure pO2, and incident light intensity I. The dependence of the initial reaction rate Ω0 on [phenol]0 showed characteristic curvature convex to the concentration axis. The pO2 dependence of both Ω0 and kap was very similar each other and showed characteristic curvature to the pO2 axis. The dependence of both Ω0 and kap on [phenol]0 was affected by the [TiO2] and I. Both Ω0 and kap were proportional to I below ca. 1×10−5 mol m−2 s−1 and to I1⁄2 above 2×10−5 mol m−2 s−1. The activation energy was 10 kJ/mol. The results were satisfactorily explained by the equation;Ω=φ·OHIan\fracKO2pO21+KO2pO2·\frac[phenol][phenol]0+β,where Ω is the reaction rate; φ·OHIan, a parameter related to the formation rate of ·OH radicals or real reactive species; KO2, the equilibrium constant of Langm...

An overview of semiconductor photocatalysis

Abstract: The interest in heterogeneous photocatalysis is intense and increasing, as shown by the number of publications on this theme which regularly appear in this journal, and the fact that over 2000 papers have been published on this topic since 1981. This article is an overview of the field of semiconductor photocatalysis : a brief examination of its roots, achievements and possible future. The semiconductor titanium dioxide (TiO 2 ) features predominantly in past and present work on semiconductor photocatalysis; as a result, in the most of the examples selected in this overview to illustrate various points the semiconductor is TiO 2 .

Review of the anatase to rutile phase transformation

Abstract: Titanium dioxide, TiO2, is an important photocatalytic material that exists as two main polymorphs, anatase and rutile. The presence of either or both of these phases impacts on the photocatalytic performance of the material. The present work reviews the anatase to rutile phase transformation. The synthesis and properties of anatase and rutile are examined, followed by a discussion of the thermodynamics of the phase transformation and the factors affecting its observation. A comprehensive analysis of the reported effects of dopants on the anatase to rutile phase transformation and the mechanisms by which these effects are brought about is presented in this review, yielding a plot of the cationic radius versus the valence characterised by a distinct boundary between inhibitors and promoters of the phase transformation. Further, the likely effects of dopant elements, including those for which experimental data are unavailable, on the phase transformation are deduced and presented on the basis of this analysis.