Contribution à l’étude de la dégradation photochimique de polluants organiques par les oxyhydroxydes de Fe (III) en solution aqueuse en phase hétérogène

Abstract

The effectiveness of Goethite (GOE) in inducing the photodegradation of organic pollutants under artificial and solar irradiation in a heterogeneous medium and in aqueous solution was the main objective of this study. We used four organic pollutants of the phenol family (RP, BBP, BCP, phenol) whose chemical structure differs depending on the substitute nature. In the absence of light and in our experimental conditions, two distinct behaviors were observed as a function of the pollutants studied during the mixing of the GOE-substrate. Indeed, in the Phenol-GOE mixture, no interaction was observed whereas a slow reaction, in the presence of the GOE, was demonstrated with RP, BBP and BCP. This interaction can be attributed to a low adsorption of the substrate on the GOE in the following order: BCP (15%)> BBP (12%)> RP (5%)> Phenol (1%), and this phenomenon is optimal in acidic medium. The addition of H2O2 accelerates the thermal process in RP-GOE system while an inhibitory effect was observed for the other two substrates (BBP, BCP) in the presence of GOE. The presence of carboxylic acids in the substrate-GOE system has shown that oxalic acid has a positive effect on the kinetics of BCP and RP eliminations under our experimental conditions. Under irradiation at 365 nm, the photodegradation of these pollutants by the GOE, was characterized by slow kinetics and seems to be dependent on several parameters such as the pH, the concentration of the substrate, the catalyst concentration, the oxygen and the molecular structure of the substrates. The mechanistic study reveals that the radicals HO • do not intervene in the mechanism of degradation of the phenol on the other hand they govern the reaction in the case of RP, BBP and BCP. The addition of H2O2 in a GOE suspension significantly improves the rate of photodegradation due to additional production of HO• radicals generated by the Fenton photo process. Different parameters have been studied to optimize this process. In the same way, the efficiency of the photochemical process is improved by the presence of carboxylic acid in a GOE suspension following the involvement of the heterogeneous like-Fenton process resulting from the reductive photo dissolution of the surface complex formed between the Fe (III) Goethite and oxalic acid. In order to verify the feasibility of the photochemical process in the environment, the same systems were studied under solar irradiation. The results show that such systems operate with kinetics of the same order as those observed in artificial irradiation, which can reduce the energy costs of the photochemical process.