Résumé:
The photolysis of iron(III) organic complexes in the presence of natural and simulated light was a concern for the role it plays within the environment in terms of producing hydroxyl radicals able to degrade organic products. A first part was devoted to the synthesis and characterization of iron(III) organic complexes in aqueous solution namely Fe(III)malate and Fe(III)malonate. Under light irradiation, the photolysis of the Fe(III) malate complex produced •OH radical and H2O2, however, in the case of Fe(III)malonate, •CH2COOH radical is generated without formation of H2O2. In the second part of the work, IBP was used as a model molecule to study the behavior of iron(III) organic complexes towards this pollutant. A preliminary study of the mixture complex/IBP in the dark and at room temperature was performed and confirmed the absence of interaction between the substrate and the complexes. Under irradiation at 365nm, the evolution of the mixtures complex/IBP demonstrated the disappearance of the substrate. The influence of several factors, such as pH, concentration of the complex and the substrate, oxygen and the excitation wavelength, on the photodegradation of IBP has been demonstrated. The mineralization of IBP required more time than photodegradation. The study of the mixture complex/IBP/H2O2 was compared with the previous system in kinetic
and mechanistic terms and shows an improvement in the reaction rate by the supply of H2O2 in concentration ranging from (10-4 to 10-2M). The optimization of H2O2 dose depends on the complex where 5×10-3M is the ideal concentration for Fe(III)malate, however, it is restricted 10-3M in the case of Fe(III)malonate in acidic medium (pH = 2.8). The mechanistic aspect was also taken into account and shows the role of the oxidative radicals involved in the photochemical process which would involve the radical •OH for the Fe(III)malate then the conjugated effect of the radicals •CH2COOH and •OH particularise the case of Fe(III)malonate. In the combined system an additional production of •OH improved the performance of the previous system. Seven photoproducts were identified by HPLC-MS during the irradiation of the Fe(III)MO/IBP mixture under irradiation at 365nm and the corresponding reaction mechanism was proposed. Experiments in the natural environment have been carried out under natural irradiation and show the feasibility of the photochemical process in the environment. In addition, the presence of certain elements present in aquatic environment such as humic substances and metals have been examined and reveal the influence of these elements on the photochemical process.
