Résumé:
The work is a contribution to the study of photodegradation of anionic surfactant
photoinduced by Fe(III) salts in aqueous solution.
In the first part of the thesis, a study of surfactant disappearance in darkness and at
ambient temperature is reported. In the presence of Fe(III), the surfactant shows a
complex and specific behavior ; a rapid complexation reaction followed by
precipitation and by a much slower reaction corresponding to a redox process, favored
at high Fe(III) concentrations. The effect of alkyl chain length is also presented: three
molecules with different chain lengths were studied and have showed different
interactions towards Fe(III).
In the second part, the degradation of the substrate by excitation at 365 nm of
aquacomplexes of Fe(III) in aqueous solution is presented. The most active species in
terms of hydroxyl radical formation is shown to be the monomeric complex
Fe(OH)2+. The efficiency of the degradation ,which is mainly due to the attacks by
these radicals, was proved .
The suggested mechanisms are, firstly characterized by the attack of the radicals on
preferential sites which depend on the molecular structure, and where the methylene
group of the hydrophobic chain seems to be the main target of this species, secondly
by the action of dissolved oxygen which leads to the formation of photoproducts such
as alcohol and carbonyl compound. Due to its redox properties, Fe(III) has a non
negligible role in the process of organic compound degradation.
The degradation of these molecules has been followed until it reaches a complete
mineralisation. The results obtained under solar excitation show the efficiency of the
system Fe(III)/UV under natural conditions.
The use of Fe(III) photoreactivity can be thus considered as an interesting method to
eliminate organic pollutant such as alkylbenzene sulfonate from the aqueous phase.
