Résumé:
The photodegradation of the herbicide phenylurea by using a natural iron oxide (NIO) α-Fe2O3 in
aqueous solution at acidic pH has been undertaken. The NIO was characterized by the Raman
spectroscopy method. The degradation pathways and the formation of by-products were studied. A
high-pressure mercury lamp and sunlight were employed as light source. Fenuron
photodegradation using NIO with oxalic acid followed the pseudo-first order kinetics, the optimal
experimental conditions were [oxalic acid] 0 = 10−3 M and [NIO] = 0.1 g L−1 at pH 3. NIO/oxalic
acid/UV system led to a low fenuron half-life (32 min). The results were even better when solar
light is used (15 min). The effect of four carboxylic acids; oxalic, citric, tartaric and malic acids on
the degradation efficiency was studied. Oxalic acid was the most effective carboxylic acid used on
the fenuron photodegradation with NIO at pH 3. The analytical study showed many aromatic
intermediates, short-chain carboxylic acids and inorganic ion.
The role of dissolved oxygen (DO) in degradation and mineralization of fenuron in the photo
Fenton-like system by using the NIO was also studied; the NIO was used as an iron source. The
DO effect has been elucidated by carrying out experiments with and without oxygen, it has been
found that the degradation and mineralization rate were strongly affected by change in DO
concentration. In absence of oxygen, there is no photo-Fenton-like because of the lack of hydrogen
peroxide, the degradation was caused only by the photo-reduction of Fe(III) complex in this case.
Oxygenation improved the hydrogen peroxide production under irradiation. The mass balance of
the reactive species showed that dissolved oxygen was the main reactive consumed during the
process. The toxicity decrease with irradiation time proves that the intermediates generated during
photo-oxidation by the photo-Fenton-like system by using a NIO are less toxic than fenuron.
