Contribution à l’élimination de colorants (Vert de méthyle et Bromocrésol pourpre) par procédés photochimiques en phase homogène (séparés et mélangés), en phase hétérogène en milieu aqueux et par adsorption (Vert de méthyle) sur ZnO.

Abstract

The study was aimed to study and to compare efficiences of photochemical processes (direct photolysis and advanced oxidation processes POAs) in the degradation of two dyes: the méthyle green and purple Bromocresol. These experiments have occurred in homogeneous phase where the two dyes were studied separately, in a binary mixture and in heterogeneous phase by using ZnO / UV and TiO2 (PC500) / UV. In Direct photolysis (365 nm and solar light), the elimination yields is weak, mainly, in artificial light. However and at 254 nm, the BCP only conducts to good results comparatively to these of MG. In another part, a total decolorization of both substrates is obtained by using a photosensitizer: acetone (10-1 mol. L-1). In photooxidation (H2O2/UV et S2O8-2/UV), this process was much efficient due to the participation of radicals •OH and SO4•-, this work was undertaken by taking into account the sensitivity of both dyes in presence of H2O2 and S2O8-2 in absence of light where we observe an insensitivity of BCP towards H2O2 but a sensitivity of MG for H2O2> 10-5M. In this research, other processes have led also to a good elimination like Fe2+/ H2O2/ UV (254 nm) and Fe3+/ H2O2/ UV (254 nm). The results obtained with these systems, were much more probants comparatively with Fenton and Like-Fenton. For the binary system, it was observed in one part that the decolorization of the dye decreases with the addition of the second dye and in another part that the process acetone/UV is the best system comparatively to direct photolysis UV and H2O2 / UV. Besides, no change in the kinetics models is observed in the binary system. In photocatalysis, the elimination of MG and BCP was total with ZnO/UV and TiO2 (PC500)/UV where this one is related directly to radical •OH. Studies were also conducted in sunlight and demonstrate the superiority of this latter comparatively to the artificial light (99, 74% in 60 minutes for MG and 100% in 120 minutes for BCP). The Langmuir Hinshelwood model describes correctly this process. It should be mentioned that in absence of light, MG showed a better adsorption capacity than BCP where it reached 92% in 180 minutes. The monitoring function of the DCO elimination showed that it depends to the organic matter and decreases over time.