Résumé:
This work aims to study and evaluate the efficiency of a photo- catalytic process photoFenton-type for the removal from aqueous medium of an azo dye (orange methyl) and a
pesticide (linuron) belonging to phenylurea family. It was for objective to study (or to
investigate) the photocatalytic activity of a local clay rich in iron oxide for the degradation of
certain kind of organic compounds, in particular dyes and pesticides.
The first part of this work has been devoted to the acquisition of some local clay and the
obtaining of their characteristic properties by a few characterization methods such as: thermal
analysis (ATD and ATG), scanning electron microscope, X-ray diffraction, UV-visible
spectroscopy and X-ray fluorescence.
The adsorption kinetics of two pollutants showed that the equilibrium is reached practically in
30 minutes. The adsorption rate was rapid at the first 15 minutes of the process and then
becomes slow for the rest of stirring time to reach equilibrium after 30 minutes.
The photo-degradation process of heterogeneous photo-Fenton type (clay/pollutant/oxalic
acid/UV system) was studied by monitoring the change in the concentration of organic
pollutants using the UV-Vis spectroscopic analysis technique as a function of irradiation time.
The degradation was studied by investigating the effect of different operational parameters
such as: the initial pH, the concentration of the catalyst and the concentration of organic
materials.
The results indicated that the photodegradation rate of two pollutants was clearly increased
in the presence of clay compared with the direct photolysis. The introduction of oxalic acid
considerably improved the photocatalytic process (about 90% removal). The optimal
conditions for a better degradation were obtained for: [clay] = 1 g/L and acidic pH (between 3
and 4) in the presence of [oxalic acid] = 10-2 M.
The exposition of the photocatalytic system to sunlight causes the disappearance the organic
pollutant in a significant way. This fact is very promising and highlighting the possibility of
using sunlight, a source of renewable and free energy as an alternative to UV radiations for
the elimination of organic pollutants from the aquatic environment.
