Abstract:
This doctoral work focused on the study of the elimination of an herbicide, the linuron, in
aqueous phase, using various degradation processes especially iron oxides. The aim is to
apply these methods for the depollution of aqueous effluents related to the fabrication and the use of pesticides. Analytical tools for the mineralization decomposition kinetics and the
identification of by-products of degradation have been used. Hydrogen peroxide and
carboxylic acids addition significantly improves the degradation and mineralization due to the production of strong oxidizing radicals. Moreover, the implication of radical species has been demonstrated in the studied systems as evidenced by the addition of radical inhibitor
(isopropanol). In the first part, the degradation of linuron was carried out in a homogeneous
medium. The speed degradation constants were determined for the different processes (UV,
H2O2 / UV, H2O2 / Fe2+ / UV). In the second part, the heterogeneous systems using a natural
iron oxide were studied. The main photoproducts were identified by UHPLC / MS and their
kinetics were drawn. Mineralization has been followed and degradation mechanisms have
been proposed. These mechanisms primarily involve (i) the hydroxylation of the aromatic ring with or without simultaneous dechlorination, (ii) the N-demethylation of N-methylurea and (iii) the N-demethoxylation of substituted-N-methoxyurea. Finally, linuron degradation by natural iron oxide (NIO) was compared with the photocatalytic system involving a labsynthesized nanoscale iron oxide (NPs). It appeared that the degradation in NIO H2O2/ UV and NPs/ H2O2/ UV systems is effective in acid while the pH does not play an important role in NIO/ UV and NPs/ UV system.
