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 Mn 2+ 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 MnO 6 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 Mn 4+ cations, is balanced mainly by interlayer Mn 3+ 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.

Energetic basis of catalytic activity of layered nanophase calcium manganese oxides for water oxidation

“…S5) shows an endotherm for water loss at 142°C and two additional endotherms at 745°C and 887°C, which may represent both water and oxygen loss, as well as an exothermic peak at 650°C possibly caused by sample coarsening. Consistent with previously reported lamellar structures for other Mn-oxide materials (15)(16)(17)(18)(19)(20), similar structures for these CaMnO materials are suggested by XRD (Fig. S2) and confirmed by low-resolution TEM (Fig.…”

“…Because the capability for efficient water oxidation is unique to photosystem II among all biological photosystems (6, 7), these CaMnO materials that mimic the elemental composition, manganese oxidation state, and particle size of the photosynthetic water oxidation center are of special interest (8)(9)(10)(11)(12). Although a number of other metal compounds function as water-oxidizing catalysts (13), many contain rare and expensive metals like iridium and ruthenium; the advantage of manganese oxides (Mn-oxides) is that they are earth-abundant, inexpensive, and environmentally friendly (1)(2)(3)(4)(5)14).CaMnO phases have short-range order structure and lamellar morphology (12), which are hallmarks of phyllomanganates (classically known as hydrous Mn-oxides), and they possess a layered structure (15)(16)(17)(18)(19)(20). In this family of structures, manganese octahedra (and vacancies) form the layers, and charge-balancing cations (i.e., alkali and alkaline earth ions, protons) and water occupy the interlayer space.…”

“…CaMnO phases have short-range order structure and lamellar morphology (12), which are hallmarks of phyllomanganates (classically known as hydrous Mn-oxides), and they possess a layered structure (15)(16)(17)(18)(19)(20). In this family of structures, manganese octahedra (and vacancies) form the layers, and charge-balancing cations (i.e., alkali and alkaline earth ions, protons) and water occupy the interlayer space.…”

Sorption and desorption of tetracycline on layered manganese dioxide birnessite

“…7), corresponding to the 001 and 002 reflections and the 20, 11 band of a birnessite with turbostratic disorder (Drits et al 2007;Grangeon et al 2010). With an increase in TC loading, a small peak at the low-angle side with a d-spacing of *9.8 Å started to show up.…”

Use of Iron Powder to Obtain High Yields of Leptothrix Sheaths in Culture

“…The sheaths that formed in the 0.14 g/L Fe powder medium showed a broad peak between 2θ = 15° and 31° (highest at 2θ = 20°), which was probably derived from C-containing constituents of bacterial and/or medium origin [23], and no remarkable peaks for the presence of Fe oxides were detected (line B of Figure 4). The sheaths in the 1.4 g/L Fe powder medium showed slight peaks at 2θ = 35° and 61° suggesting the presence of XRD-amorphous 2Fh (line C of Figure 4), similar to those from the Fe plate medium.…”