Cation Effects on the Layer Structure of Biogenic Mn-Oxides

摘要

Biologically catalyzed Mn(II) oxidation produces biogenic Mn-oxides (BioMnO_x) and may serve as one of the major formation pathways for layered Mn-oxides in soils and sediments. The structure of Mn octahedral layers in layered Mn-oxides controls its metal sequestration properties, photochemistry, oxidizing ability, and topotactic transformation to tunneled structures. This study investigates the impacts of cations (H~+, Ni(II), Na~+, and Ca~(2+)) during biotic Mn(II) oxidation on the structure of Mn octahedral layers of BioMnO_x using solution chemistry and synchrotron X-ray techniques. Results demonstrate that Mn octahedral layer symmetry and composition are sensitive to previous cations during BioMnO_x formation. Specifically, H~+ and Ni(II) enhance vacant site formation, whereas Na~+ and Ca~(2+) favor formation of Mn(III) and its ordered distribution in Mn octahedral layers. This study emphasizes the importance of the abiotic reaction between Mn(II) and BioMnO_x and dependence of the crystal structure of BioMnO_x on solution chemistry.