Phototransformation de tensioactifs anioniques induite par les sels de fer (III) en solution aqueuse.

Abstract

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.