Photoelectrochemistry with Colloidal Semiconductors; Laser Studies of Halide Oxidation in Colloidal Dispersions of TiO2 and α-Fe2O3

Authors

  • Jacques Moser,

    1. Institut de chimie physique, Ecole Polytechnique Fédérale, 1015 Lausanne, Switzerland
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  • Michael Grätzel

    Corresponding author
    1. Institut de chimie physique, Ecole Polytechnique Fédérale, 1015 Lausanne, Switzerland
    • Institut de chimie physique, Ecole Polytechnique Fédérale, 1015 Lausanne, Switzerland
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Abstract

Aqueous sols of TiO2 (anatase, particle radius 25 Å) were excited with (347.1 nm)-laser light and the reaction of valence-band holes with halide ions (X = I, Br, Cl) was investigated. Hole transfer takes place within the duration of the (10 ns)-laser pulse and results in the formation of anion radicals according to the sequence:

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The quantum yield of Xmath image increases in the order Clmath image < Brmath image < Imath image, attaining 0.8 for Imath image at pH 1. It is affected by pH, halide concentration and the presence of a protective agent for the sol.

RuO2 deposited onto TiO2 enhances markedly Clmath image and Brmath image -formation, but has no effect on the yield of Imath image.

Laser-photolysis investigation of halide oxidation were also carried out with colloidal Fe2O3 (particle radius 600 Å). For I2−formation, the quantum yield exceeds 0.9 indicating almost quantitative hole scavenging by iodide.

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