Etude de l’élimination de deux colorants (Cristal violet et Jaune d’alizarine) par des procédés photochimiques en milieu homogène (lumière artificielle et solaire) et en milieu hétérogène (TiO2/UV et ZnO/UV)

Abstract

This study is focused in the application of different advanced oxidation processes in a homogeneous and heterogeneous phase for the treatment of two dyes: the AY and the CV. The direct photolysis of dyes by the artificial light (254nm and 365nm) and solar light is slow and can be accelerated by increasing of intensity of photon flux incident, or by adding a photosensitizer such as acetone at high concentration. In the case of the two dyes studied, it has been shown that the rate of decolorization by the AOPs in a homogeneous medium such as H2O2/UV, S2O82-/UV and H2O2/S2O82-/UV, has been substantially improved compared to that obtained by UV photolysis and that the rate depends on the experimental parameters such as: concentration of substrate, concentration of catalyst and pH of medium. This improvement could be related to the production of HO• and SO4•- radicals. Regarding the system UV/S2O82-/H2O2, we have observed that efficiency decreased slightly due to a competition effect. On the other hand, the persulfate can generate sulfates radicals ions by heat activation in absence of light. The degradation of the two dyes has been more effective in Photo-Fenton and Photo-like-Fenton system than in the Fenton and Fenton-like systems respectively where the performances of these systems could be optimised by variation of the experimental parameters such as the pH, the [H2O2]/ [Fe2+] and the [H2O2]/ [Fe3+] ratio. In the (Fe2+/ S2O82-) and the (UV/Fe2+/S2O82-) system, the persulfate acts on the JA similarly to H2O2 compared to the Fenton and Photo-Fenton processes. In heterogeneous photocatalysis, the degradation of the JA and the CV has been studied using different semiconductors (TiO2, ZnO, ZnOpure-Bi2O3). The photocatalysis study of the two dyes by the TiO2 process (Degussa P25)/UV and ZnO/UV has been presented after overseeing a low adsorption until saturation (30 minutes). Photocatalysis is influenced by various factors where this process is improved by the addition of H2O2 but has been inhibited by certain inorganic anions and alcohols. TiO2-P25 is more efficient than Tiona photocatalysts. In addition, the Langmuir-Hinshelwood model has adequately described this process. The follow up by the Chemical Oxygen Demand (DCO), confirms that the photocatalysis process leads to the decrease of the organic matter content until mineralization of pollutants. Tests in natural radiation showed a faster degradation of bith pollutant. The ZnO pure-Bi2O3/UV process is more efficient than the two ZnO commercial/UV and ZnO pur/UV processes in terms of degradation.