Otman Abida

Université Blaise Pascal - Clermont-Ferrand II, Clermont, Auvergne, France

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Publications (7)11.49 Total impact

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    ABSTRACT: The 4-chlorophenol (4-CP) degradation photoinduced by Fe(iii)-citrate complex was investigated upon irradiation at 365 nm at different pHs (2.0, 3.0, 4.0 and 6.0). The best efficiency for 4-CP degradation in the presence of Fe(iii)-citrate was at pH 3.0 with a value of quantum yield equal to 0.026. This effect is mainly attributed to speciation of Fe(iii)-citrate complex which is very sensitive to the pH. Quantum yields of 4-CP degradation, Fe(iii)-citrate disappearance and Fe(ii) formation were carried out at wavelength 365 nm at different pHs (3.0 and 6.0). The effect of the pH is less pronounced for the quantum yields of 4-CP than for Fe(iii)-citrate complex and Fe(ii) quantum yields which are species involved in the initial photochemical process. The effect of oxygen, isopropanol and Fe(iii)-citrate concentrations on the quantum yields of 4-CP degradation and also on kinetics of 4-CP disappearance was also studied. Indeed, 4-CP requires the presence of oxygen to be degraded. The disappearance of 4-CP was totally inhibited without oxygen dissolved in the solution. Oxygen is essential for the formation of oxidative species and, as a consequence, for the degradation of the pollutant.
    Photochemical and Photobiological Sciences 02/2012; · 2.92 Impact Factor
  • 01/2011;
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    ABSTRACT: Chromium(VI) reduction photoinduced by iron(III) nitrilotriacetate (FeNTA) was investigated under monochromatic excitation. 313 nm was used as the irradiation wavelength in order to minimize the absorption of the light by chromium(VI): 91% of the photons were absorbed by FeNTA at pH = 7.0. Quantum yields of FeNTA and chromium(VI) disappearance and iron(II) formation were measured at pH 2.0, 4.0 and 7.0. In all the cases, chromium(VI) reduction follows first order kinetics with maximum efficiency at pH 2.0. The observed rate constant is proportional to FeNTA concentrations up to a maximum of 6.0 x 10(-4) mol L(-1). The effect of oxygen was also investigated. If there is no large pH effect and no effect of oxygen on the quantum yields of chromium(VI) and FeNTA disappearance, the pH strongly influences the nature of the reduced chromium species. At pH 2.0, only chromium(III) was detected, whereas at pH 4.0 and 7.0 no chromium(III) resulting from chromium(VI) reduction was observed. Chromium(V) is supposed to be formed and stabilized by the chelating groups of NTA or NTA photoproducts.
    Photochemical and Photobiological Sciences 06/2010; 9(6):823-9. · 2.92 Impact Factor
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    ABSTRACT: Iron is the most abundant transition metal in the atmosphere and can play a significant role in cloudwater chemistry where its reactivity is closely related to the partitioning between Fe(II) and Fe(III). The objective of this work is to determine the total iron content and the iron speciation in a free tropospheric site, and to understand which factors influence these parameters. We collected 147 samples of cloudwater during 34 cloud events over a period of four years at the puy de Dôme summit. Besides iron we measured other chemical compounds, solar radiation, physico-chemical and meteorological parameters potentially connected with iron reactivity. The total iron concentrations ranged from 0.1 to 9.1 μM with the major frequency occurring at low levels. The pH and presence of organic complexants seem to be the most significant factors connected with total dissolved iron; while the iron oxidation state seems to be an independent factor. Light intensity, presence of complexants or oxidants (H2O2) do not influence the Fe(II)/Fe(Total) ratio, that was quite constant at about 0.75. This could be due to the potential redox that forces the Fe(II)-Fe(III) couple to the reduced form or, more probably to the complexation by Natural Organic Matter, that can stabilize iron in its reduced form and prevent further oxidation. Our field measurements did not show the diurnal cycle observed in surface water and predicted by models of atmospheric chemistry. This result prompts a more careful review of the role of iron and, by analogy, all the transition metals in atmospheric liquid phase, often over-estimated in the literature.
    Journal of Atmospheric Chemistry 01/2007; 54(3):267-281. · 1.33 Impact Factor
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    ABSTRACT: In this research work, the photochemical impact of Fe(III)-nitrilotriacetic acid complex (FeNTA) on the fate of an organic pollutant (4-chlorophenol (4-CP)) was investigated in natural waters. The quantum yields of the photodecomposition of the FeNTA complex and of Fe(II) formation, by an intra-molecular photoredox process (the first stage of the reaction) are high. This photoredox reaction represents the first step of the process leading to 4-CP disappearance. Whereas oxygen does not affect FeNTA photodegradation, 4-CP depletion requires the presence of oxygen. The radical species HO and CO3*- responsible of the degradation were identified by ESR spectroscopy under irradiation. Two different wavelength-dependent mechanisms of 4-chlorophenol degradation are proposed. It clearly appears that under solar irradiation, iron organic complexes like FeNTA can play a significant role on the fate of the organic compounds present in natural waters.
    Photochemical and Photobiological Sciences 05/2006; 5(4):395-402. · 2.92 Impact Factor
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    ABSTRACT: In this work, the comparison of 4-chlorophenol (4-CP) degradation by two different AOT processes has been performed: a) a homogeneous system with Fe(III)-NTA (1:1 complex), b) a TiO2/Fe(III)-NTA heterogeneous system. In both cases, NTA appears to play a positive role in the photochemical reaction. In the homogeneous system, the iron salt is the only absorbing species and is proved to be able to photoinduce 4-CP degradation ([4-CP] = 0.1-0.2 mM, [FeNTA] = 0.3-0.9 mM, pH 4, lambda = 365 nm). The progress of the reaction was positively affected by the FeNTA concentration, and the reaction kept going even after the total disappearance of FeNTA. However, 4-CP complete degradation requires the presence of oxygen, otherwise the reaction stops. In the heterogeneous system ([4-CP] = 2.0 mM, [FeNTA] = 1.0-2.0 mM, [TiO2] = 0.1 and 1.0 g L(-1), pH 3, lambda = 300-400 nm), an important effect of the complex on the degradation extent and on the initial reaction rate can be seen, which overcomes the effect of non-complexed Fe(III). This behaviour is more important at the highest TiO2 concentration.
    Water Science & Technology 02/2004; 49(4):123-8. · 1.10 Impact Factor
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    ABSTRACT: Iron play a significant role in atmosphere. Its reactivity depends on oxidation state and speciation. ln order to study photochemical cycle of iron in atmospheric waters, we collected cloud samples at the research station of puy de Dôme. We found very low levels: iron concentrations are ranging from 0.2 muM to 3.4 muM. The light is not an important factor towards affecting the oxidation state, in contrast with many field studies, where clear dependence from light intensity was shown. Contrary to recent studies and to chemical models iron in the cloud droplets at Puy de Dôme is mostly present as Fe(II): the ratio Fe(II)/FeTOT is 0.77 on average. No clear relationship is found between Fe and carboxylic acids. Same samples are irradiated between 300 and 450 mn in a Teflon-made reactor: H2O2, TOC, Fe^{2+}, Fe^{3+} and pH are continuously monitored during the irradiation. We observed no tendency for the Fe(II)/FeTOT ratio to increase or decrease and the DOC is not strongly varying during the irradiation. In consequence of the stability of the Fe(II)/Fe(III) ratio, we can assume that cloud water contains compounds that undergo the action of oxidants, and possibly, organic substances play an important role in this processus.
    Journal de Physique IV (Proceedings) 01/2003; 107:823-826. · 0.29 Impact Factor