Abiotic formation of methyl iodide on synthetic birnessite: A mechanistic study
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Methyl iodide is a well-known volatile halogenated organic compound that contributes to the iodine content in the troposphere, potentially resulting in damage to the ozone layer. Most methyl iodide sources derive from biological activity in oceans and soils with very few abiotic mechanisms proposed in the literature. In this study we report that synthetic manganese oxide (birnessite δ-MnO2) can catalyze the formation of methyl iodide in the presence of natural organic matter (NOM) and iodide. Methyl iodide formation was only observed at acidic pH (4–5) where iodide is oxidized to iodine and NOM is adsorbed on δ-MnO2. The effect of δ-MnO2, iodide and NOM concentrations, nature of NOM and ionic strength was investigated. High concentrations of methyl iodide were formed in experiments conducted with the model compound pyruvate. The Lewis acid property of δ-MnO2 leads to a polarization of the iodine molecule, and catalyzes the reaction with natural organic matter. As manganese oxides are strong oxidants and are ubiquitous in the environment, this mechanism could significantly contribute to the global atmospheric input of iodine.
NOTICE: this is the author’s version of a work that was accepted for publication in Science of the Total Environment. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Science of the Total Environment, Vol. 463-464 (2013). DOI: 10.1016/j.scitotenv.2013.05.079
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Allard, Sebastien; Gallard, H.; Fontaine, C.; Croue, J. (2010)This paper demonstrates that manganese oxides can initiate the formation of methyl iodide, a volatile compound that participates to the input of iodine into the atmosphere. The formation of methyl iodide was investigated ...
Formation of iodinated organic compounds by oxidation of iodide-containing waters with Manganese DioxideGallard, H.; Allard, Sebastien; Nicolau, R.; Von Gunten, Urs; Croue, J. (2009)This study shows that iodinated organic compounds can be produced when iodide-containing waters are in contact with manganese oxide birnessite (d-MnO2) in the pH range of 5-7. In the absence of natural organic matter ...
Allard, Sebastien; Von Gunten, Urs; Salhi, E.; Nicolau, R.; Gallard, H. (2009)The oxidation of iodide by synthetic birnessite (δ-MnO2) was studied in perchlorate mediain the pH range 4-8. Iodine (I2) was detected as an oxidation product that was subsequently further oxidized to iodate (IO3). The ...