General conclusions

In our experimental conditions, we demonstrated that Fe(III) was complexed by EDDS with a ratio 1:1. We also checked the stability of Fe-EDDS complex in the dark and at room temperature. Fe(III)-EDDS is stable in the aqueous solutions in our experimental conditions (pH = 3.0 to pH = 6.0). Our results show that the pH is an important parameter for the stability of the complex and its speciation. At lower pH (<

2.0) a phenomenon of decomplexation can be proposed.

In the present study, formation of phenol from benzene was used to determine the concentration of ^•OH radicals by the photolysis of Fe(III)-EDDS complex.

Parameters, such as pH, the concentration of Fe(III) or EDDS, oxygen were all considered in the study. Results shows that the pH value has great effect on the photolysis of Fe(III)-EDDS complex in producing ^•OH. Interestingly, the maximum concentration of ^•OH radicals were observed at pH 6.0 (pH ranged from 3.0 to 6.0).

This particular point is fully in agreement with the disappearance of 2, 4-D which is higher at pH 6.0 than 3.0 in the presence of Fe(III)-EDDS complexes. The ^•OH concentration generated in the system increased also with the increase of Fe(III) or acid concentrations. The presence of high concentration of acid strongly favored the reoxidation of Fe(II) after the first photoredox process in the complex and as a consequence increased the efficiency of ^•OH radicals photoproduction.. Oxygen is a crucial factor for the formation of active radicals in the aqueous solutions. Without oxygen no formation of ·OH radical is observed in the containing Fe-EDDS complex even under irradiation.

EDDS has positive effects on the photogeneration of ·OH in the aqueous solution.

So, the Fe(III)-EDDS complex has the potential of utilizing sunlight as an irradiation source. Interestingly, the [S, S’]-isomer of EDDS was reported to be produced naturally by a number of microorganisms, such as Amycolatopsisjaponicum sp. nov.

So in the natural surface waters, such as lakes, which contain Fe(III)/Fe(II) and [S, S’]-EDDS, photochemical reactions can be induced by sunlight, and it will play an

important role in the oxidation of organic/inorganic pollutants in natural waters.

Further experimental and theoretical work is needed to fully understand the system and its application in natural aquatic or atmospheric environments.

Photodegradation of 2, 4-D and atrazine photoinduced by Fe(III)-EDDS complex was investigated in this study. Results indicate that irradiation wavelength, pH, oxygen, ratio and concentration of Fe(III)-EDDS complex and isopropanol, all have effect on the quantum yields of Fe(II) formation and 2,4-D degradation. Irradiation wavelength has a great effect on the quantum yields, both ΦFe(II) and Φ2, 4-D increase with the decrease of wavelength of irradiation. The pH 6.0 and high concentration of oxygen are all favorable for the photodegradation of 2, 4-D. In the presence of high concentration in oxygen and at pH 6.0 the total degradation of 2, 4-D and photogeneration of 2, 4-DCP are observed after 8 h of irradiation. Oxygen is necessary for an efficient degradation of 2, 4-D.

In the presence of goethite particles, the concentration of 2, 4-D was almost the same even after 39 h shaking period in the aqueous solutions. It means that there was no obvious adsorption of 2, 4-D in suspension with the presence of goethite at pH 4.0.

With the increasing of time, in evidence, nearly 9% of 2, 4-D was adsorbed on the goethite at pH 3.0, But even at pH 3.0, no more than 4% of 2, 4- D were adsorbed on the goethite in suspension after 8 h shaking period.

Degradation of 2, 4-D photoinduced by goethite with or without EDDS complex were investigated in this study. Results indicate that pH, concentrations of goethite and EDDS in suspension, isopropanol all have effect on the 2,4-D degradation. The pH 6.0 is favorable for the photodegradation of 2, 4-D in suspension with goethite and EDDS. This is fully in agreement with the results obtained in the presence of the complex Fe(III)-EDDS and prove that the degradation is effective through the formation of this complex in the system goethite, EDDS and light. As a contrary, in the presence of goethite without EDDS, pH 3.0 is favorable for the photodegradation of 2, 4-D. Isopropanol depress the photodegradation efficiency of 2, 4-D in all the cases. This is in agreement with the formation of ^•OH radical which react with

Under irradiation, the photolysis of Fe(III)-Pyr complexes could represent the source of active oxygen radicals, such as ^•OH, CO3•-

, CO2•-

, H^• and RCO2•. In the Fe(III)-Pyr system, free Fe(III) species could generate ^·OH radicals through the reaction Fe(III) + H2O + h → Fe(II) + ^•OH + H⁺. ·OH radicals could also be generated by direct photolysis of pyruvic acid with a relative quantum yield of 5 ± 3 %. Oxygen was always involved in the formation of active oxygen species. Acidic condition was favorable for this photochemical reaction.

Fe(III)-Pyr complex could enhance the photodegradation of atrazine in the aqueous solution and under irradiation. High degradation efficiency was obtained at high concentrations of Fe(III)/Pyr and at low pH, as a contrary of the complex Fe(III)-EDDS where the photoactivity is higher at pH 6.0. Four kinds of photoproducts were identified in this work. This type of complexes could be formed in the natural aquatic environment due to the presence of carboxylic acids and iron.

Thus, such complexes could influence the fate of inorganic and organic pollutants existing in the natural environment. This work could help us to fully understand the photoreaction processes concerning Fe(III)/Pyr complex and its potential for the degradation of pollutants in the natural surface and atmospheric water under solar irradiation.

The main conclusion of this thesis is that iron-organic acids complexes represent a class of species which can play a very important role in the environment for the transformation and as a consequence the fate of organic matter in aquatic compartments. We demonstrated that these complexes are photochemically (under solar light) in a large range of pH and in different physico-chemical properties of the aqueous solution.

VIII

APPENDIX