Kinetics of heterogeneous photocatalytic decomposition of phenol over anatase TiO2 powder.

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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 Langmuir adsorption of O2; β, the ratio of the combined first-order rate constant of the reaction of ·OH with species other than organic compounds to the second-order rate constant of the reaction of ·OH with phenol.
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