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.
