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Structure of nanocrystalline phyllomanganates produced by freshwater fungi

Abstract : The crystal structures of biogenic Mn oxides produced by three fungal strains isolated from stream pebbles were determined using chemical analyses, XANES and EXAFS spectroscopy, and powder X-ray diffraction. The fungi-mediated oxidation of aqueous Mn2+ produces layered Mn oxides analogous to vernadite, a natural nanostructured and turbostratic variety of birnessite. The crystallites have domain dimensions of ~10 nm in the layer plane (equivalent to ~35 MnO6 octahedra), and ~1.5-2.2 nm perpendicularly (equivalent to ~2-3 layers), on average. The layers have hexagonal symmetry and from 22 to 30% vacant octahedral sites. This proportion likely includes edge sites, given the extremely small lateral size of the layers. The layer charge deficit, resulting from the missing layer Mn4+ cations, is balanced mainly by interlayer Mn3+ cations in triple-corner sharing position above and/or below vacant layer octahedra. The high surface area, defective crystal structure, and mixed Mn valence confer to these bio-minerals an extremely high chemical reactivity. They serve in the environment as sorption substrate for trace elements and possess catalytic redox properties.
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Sylvain Grangeon, Bruno Lanson, Naoyuki Miyata, Yukinori Tani, Alain Manceau. Structure of nanocrystalline phyllomanganates produced by freshwater fungi. The American Mineralogist, 2010, 95 (11-12), pp.1608-1616. ⟨10.2138/am.2010.3516⟩. ⟨insu-00544688⟩

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