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Laser Flash Photolysis Study of the Photocatalytic Step of the Photo-Fenton Reaction in Saline Solution

Authors

  • Amilcar Machulek Jr.,

    1. Instituto de Química, Universidade de Säo Paulo, CP 26077, Säo Paulo 05513-970, Brazil
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  • Carolina Vautier-Giongo,

    1. Instituto de Química, Universidade de Säo Paulo, CP 26077, Säo Paulo 05513-970, Brazil
    2. Departamento de Engenharia Química, Escola Politécnica, Universidade de Söo Paulo, 05508-900, Säo Paulo, Brazil
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  • José E. F. Moraes,

    1. Departamento de Engenharia Química, Escola Politécnica, Universidade de Söo Paulo, 05508-900, Säo Paulo, Brazil
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  • Claudio A. O. Nascimento,

    1. Departamento de Engenharia Química, Escola Politécnica, Universidade de Söo Paulo, 05508-900, Säo Paulo, Brazil
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  • Frank H. Quina

    Corresponding author
    1. Instituto de Química, Universidade de Säo Paulo, CP 26077, Säo Paulo 05513-970, Brazil
    • To whom correspondence should be addressed: Instituto de Química, Universidade de Säo Paulo, CP 26077, Säo Paulo 05513-970, Brazil. Fax: 55-11-3815-5579; e-mail: quina@usp.br

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  • This paper is part of a special issue dedicated to Professor J. C. (Tito) Scaiano on the occasion of his 60th birthday.

ABSTRACT

The photo-Fenton reaction (Fe2+/Fe3+, H2O2, UV light) is strongly inhibited by high concentrations of added chloride ion. In this work, the effect of added chloride ion on the photocatalytic step that converts Fe(III) back to Fe(II) is studied by nanosecond laser flash photolysis over a wide range of pH (1.0-3.3) and concentrations of Fe(III) (0.1-1.0 mM) and chloride ion (0.05-0.75 M). An explicit mechanistic model based on the preferential formation of the less-reactive Cl2*- radical anion via two routes (competitive photolysis of the iron(III)-chloride complex to chlorine atoms instead of the desired hydroxyl radical and pH-dependent scavenging of the hydroxyl radical by chloride ion) is proposed. This model, which fits the laser flash photolysis data for the production and decay of Cl2*- over the entire range of conditions investigated, suggests that inhibition of the photocatalytic step of the photo-Fenton process in the presence of chloride ion can be circumvented by maintaining the pH of the medium at or slightly above 3.0 throughout the reaction.

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