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Cristallochimie des phyllomanganates nanocristallins désordonnés. Implications pour l'adsorption d'éléments métalliques

Abstract : Vernadite is a nanocrystalline phyllomanganate ubiquist in nature and exhibiting a turbostratic stacking, that is systematic random stacking faults between adjacent layers. The presence of layer vacancies and/or of manganese cations with mixed oxidation states induces a strong deficit of charge, balanced by the presence of hydrated interlayer cations. These features provide vernadite with cation adsorption capacities, and/or redox potential that are responsible for its reactivity in superficial environments where it strongly influences the fate of numerous organic and metallic pollutants. Despite this role, the structures of vernadite and of its synthetic analogue delta-MnO2 are still incompletely determined as their structural disorder precludes the use of common structure refinement methods. We have thus applied a specific approach, coupled both with chemical and synchrotron-based spectroscopic (XANES and EXAFS) techniques, to determine the structures of delta-MnO2 and of vernadites produced by freshwater fungi together with the structural features responsible for their reactivity. The structure of delta-MnO2 evolves with pH and time with a strong potential influence on its reactivity. Structural mechanisms of adsorption of model metals (Ni and Zn) on delta-MnO2 were also determined. Adsorption occurs mainly above/below vacant layer sites, adsorption mechanisms being dependent on the metal and on the actual structure of delta-MnO2
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Submitted on : Thursday, August 27, 2009 - 11:17:13 AM
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  • HAL Id : tel-00378590, version 2

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Sylvain Grangeon. Cristallochimie des phyllomanganates nanocristallins désordonnés. Implications pour l'adsorption d'éléments métalliques. Sciences de la Terre. Université Joseph-Fourier - Grenoble I, 2008. Français. ⟨tel-00378590v2⟩

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