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Rôle de l'état de surface du fer métal sur le mécanisme et la cinétique de décomposition de colorants azoïques

Abstract : Wastes produced by textile industry involve strongly recalcitrant molecules which can be hardly degraded by water treatment technology. The aim of fuis work is to monitor, understand and evaluate the mechanisms of azo- dyes degradation in aqueous solution in the presence of metallic iron in weak acidic solutions. Three dyes with specific molecular structure were investigated: orange II. orange I and orange GG. Surface and interface analytical techniques like: FTIR-external reflection spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy were applied to monitor interface phenomena. UV-Vis spectrophotometry and atomic absorbance spectroscopy (AAS) were used to perform the solution analysis. Metallic iron interaction with and without dye solution were investigated. There are striking relationships between solution pH, iron surface composition, kinetics and reaction pathways of different orange decompositions. At pH 3 a thin surface layer is formed composed by FeO and Fe(OH)2 which thickness remains constant over reaction time. At pH 5 . these products are intermediates and lepidocrocite is the final surface layer product which amount increases with time. The presence of dye in the soJution contacted with metaJJic iron does Dot produce significant ch.wges in the iron surface layer composition already mentioned but modify importantly the oxidation rates. The decomposition mechanisms were elucidated. The first step of reaction involves dye adsorption through sulphonate groups. Afterwards, a reduction step lead to the cleavage of -N=N- bond and the formation of two amine intermediates. One stars adsorbed on the surface and undergoes immediately further decomposition white the second one is released to solution. Generally, the lower the open circuit potential (OCP) of iron, the faster the dye decomposition. Though, orange GG does not show this relationship. Modifications of iron surface layer composition and structure provide changes in kinetics and reaction pathways.
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Gonzalo Monte Atenas. Rôle de l'état de surface du fer métal sur le mécanisme et la cinétique de décomposition de colorants azoïques. Sciences de la Terre. Institut National Polytechnique de Lorraine, 2004. Français. ⟨NNT : 2004INPL032N⟩. ⟨tel-01750049⟩



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