"Elimination de deux colorants (Vert de Bromocrésol et Rouge de Crésol) de structure semblable, par des techniques photochimiques et sonochimiques en milieu aqueux homogène et hétérogène"

Abstract

"The aim of this study was to compare the efficiency obtained by some processes coupled or no with light (artificial and natural) and also by sonchemical technics in the course of the degradation of two dyes having similar structure: the Bromocresol Green and the Cresol Red -In direct photolysis (254 nm, 365 nm and solar light), the yield of elimination was weak, mainly, in artificial light. However, the CR, this yield was better than that obtained in the BCG but in solar light only. Besides, this process has been improved sensitively by increasing the light intensity in one part (artificial) and by adding a sensitizer: the Acetone 0.1M in another part. The oxidation conducted in homogeneous medium has allowed an effective degradation of both substrats, especially, when these systems were coupled with light (artificial) : H2O2/UV and S2O8 2-/UV. This could be attributed to radicals OH• and SO4 •- . It should be mentioned that no reaction occurred with both dyes and S2O8 2- , H2O2 in absence of light. Similar results have been obtained with Fe2+ and Fe3+. When treated by Fenton and like-Fenton, the efficiency reached an average yield of degradation but a better one when they were coupled with light: Photo-Fenton and like-photo- Fenton. The performance of these two systems, have been optimized by varying experimental parameters like: pH, concentration of Fe2+, of Fe3+ and H2O2. The choice of the ratio H2O2/ Fe2+ or H2O2/ Fe3+ has been very necessery for this work. The oxidation in heterogeneous medium via systems like: ZnO/UV and TiO2/UV, has allowed also an effective elimination of the two substrates. Before any experimental work, we observed no adsorption of both dyes in those supports for a time equal to 30 minutes. The decolorization of both dyes was total when treated by TiO2 (PC500)/UV and ZnO/UV. This could be attributed also to radicals OH• produced by these two supports and the light. The kinetic model of Langmuir- Hinshelwood described correctly the photocatalytic process in the two cases. In solar light (TiO2 PC500/Solar), the experimental results were better than those obtained in artificial light. The mineralization process has been followed by the DCO technic and showed a sensitive decreased with time. The sonochemical systems like: US, US / H2O2 and US/ S2O8 2- have allowed also a good yield in the course of the degradation process for both dyes."