A large number of microorganisms are responsible for the oxidation of Mn2+(aq) to insoluble Mn3+/4+ oxides (MnO x) in natural aquatic systems. This paper reports the structure of the biogenic MnOx, including a quantitative analysis of cation vacancies, formed by the freshwater bacterium Leptothrix discophora SP6 (SP6-MnOx). The structure and the morphology of SP6-MnOx were characterized by transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS), including full multiple-scattering analysis, and powder X-ray diffraction (XRD). The biogenic precipitate consists of nanoparticles that are approximately 10 nm by 100 nm in dimension with a fibrillar morphology that resembles twisted sheets. The results demonstrate that this biogenic MnO x is composed of sheets of edge-sharing of Mn4+O 6 octahedra that form layers. The detailed analysis of the EXAFS spectra indicate that 12 ± 4% of the Mn4+ layer cation sites in SPG-MnOx are vacant, whereas the analysis of the XANES suggests that the average oxidation state of Mn is 3.8 ± 0.3. Therefore, the average chemical formula of SP6-MnOx is Mn+ yMn3+0.12[□0.12Mn 4+0.88]O2· zH2O, where M n+y represents hydrated interlayer cations, □0.12 represents Mn4+ cation vacancies within the layer, and Mn3+0.12 represents hydrated cations that occupy sites above/below these cation vacancies.
ASJC Scopus subject areas
- Colloid and Surface Chemistry