Degradation photochimique des colorants cationiques sur des supports inorganiques chromophores en solution aqueuse

Abstract

The main objective of this study is to test the effectiveness of a natural miniral through the study of the elimination of two polluting models "methylene blue and rhodamine B" in aqueous solution. In a homogeneous phase, various methods have been established to degrade the both dyes; direct photolysis, photo-oxidation with hydrogen peroxide and persulfate as well as by the Fenton reagent and photo-Fenton. The results showed that the photo-Fenton process at 254 nm is the most efficient. The analyses by XRD, IR, Raman and X-ray fluorescence of the natural mineral, which comes from Souk-Ehres North-East of Algeria, confirmed that this mineral consists of 89 % of hematite, this high content of iron lead us to use this support as a catalyst (source of iron ions) to create the photo-Fenton-like process in the presence of carboxylic acids. Among the carboxylic acids studied, oxalic acid is the most effective for the dissolution of natural iron oxide, therefore for the photodegradation of the MB and RhB. Indeed, under irradiation, oxalic acid forms a complex with iron oxide and leads to the release of Fe(III) ions. In solution and by the photoreduction reaction, the Fe(III) ions are transformed into Fe(II) and leads to the formation of hydrogen peroxide launching a photo-Fenton reaction, leading to the formation of hydroxyl radicals. The study of the influence of several physico-chemicals parameters (effect of acid concentration, temperature, O2, pH, nature of radiation ...) on the efficiency of NIO/OA/UV process yielded to the determination of optimal conditions for the dyes removal. The abatement rates of COD for MB and RhB by this process were very reasonable, confirming the effectiveness of the NIO in the treatments of wastewaters. The use of natural iron in the presence of oxalic acid under solar irradiation reduces energy costs, and required time for a total elimination of dyes.