Formation of nano-crystalline todorokite from biogenic Mn oxides

High Co-doping promotes the transition of birnessite layer symmetry from orthogonal to hexagonal

“…5. The oscillations match quite well with those of birnessite, i.e., the sharp diagnostic features at 6.6, 8.0 and 9.1 Å − 1 (Mckeown and Post, 2001;Manceau et al, 2004;Marcus et al, 2004;Webb et al, 2005;Feng et al, 2010;Atkins et al, 2014). The shapes of the two oscillations at~8.0 and~9.1 Å −1 are known to be affected by the type of symmetry that exists in the birnessite layers, due to the distribution order of layer Mn(III).…”

“…Because of their natural ubiquity, large amounts of structural defects and negative charges, high redox potential and large specific surface area, birnessites play an important role in the geochemical fate of heavy metals Feng et al, 2007;Peacock and Sherman, 2007a,b;Zhu et al, 2010b;Villalobos et al, 2014) and other pollutants (Li et al, 2015) in the environment. Birnessite is also the precursor of other Mn oxides, such as todorokite (Bodei et al, 2007;Feng et al, 2010;Atkins et al, 2014;Manceau et al, 2014). Natural birnessite is typically highly disordered and occurs in a finely dispersed state, commonly mixed with other phases such as phyllosilicates and Fe oxyhydroxides, thus varieties synthesized under various physicochemical conditions in the laboratory are considered analogs of natural birnessites and are used to conduct mineralogical research and to model naturally occurring redox and adsorption processes.…”

Structural study of biotic and abiotic poorly-crystalline manganese oxides using atomic pair distribution function analysis

“…However, a layered structure of BioMnO x , produced by the same type of bacteria, but in liquid media, was also reported (Grangeon et al, 2010). Todorokite and other tunnel Mn oxides are believed to be formed from layered Mn oxide precursors in the presence of template cations (Feng et al, 2010). These results suggest a direct formation pathway for todorokite from Mn 2+ oxidation without layered Mn oxides as precursors.…”

Diversity of Mn oxides produced by Mn(II)-oxidizing fungi

“…The dimensions of the fungal Mn oxides differ from those typically observed for bacterial Mn oxides. In particular, the fungal Mn oxides are smaller in diameter along the a axis (<6 nm v. 10-50 nm) but longer along the b axis (up to 1 lm v. <500 nm) than most bacterial Mn oxides (Bargar et al, 2009;Feng et al, 2010;Villalobos et al, 2003). Consistent with our results, however, recent characterization of Mn oxides formed by freshwater fungi found birnessite with average dimensions of $1.5-2.2 nm ($2-3 layers) perpendicular to the layer plane (Grangeon et al, 2010).…”

“…Despite the large diversity in Mn oxide structures, the dominant biogenic Mn oxide formed under circumneutral pH is a nanocrystalline phyllomanganate similar to hexagonal birnessite or dMnO 2 , the synthetic analog of vernadite Jurgensen et al, 2004;Nelson et al, 1999;Villalobos et al, 2006;Webb et al, 2005a). Abiotic transformations and ageing of these initial disordered biogenic phases results in the formation of more crystalline Mn phases, including todorokite and feitknechtite Feng et al, 2010). Oxidation at temperatures ranging from 3 to 70°C at circumneutral pH results in a wider range of Mn oxides, varying in structure and average oxidation state, which correspond well with the thermodynamic stability fields for these phases (Mandernack et al, 1995).…”