Anionic effect on nanostructure and morphology of bio-schwertmannite dynamically produced within cellular reproduction

Schwertmannite has been considered as the host mineral and potentially excellent adsorbent of contaminates from waters, and it has various morphologies of spheroid with pincushions, whiskers, hedge-hogs, and needles. In this work, using the (high-resolution transmission and field-emission scanning) electron microscopes, we studied nanostructure, morphological evolution, and difference in chemical composition for the produced schwertmannites in the cell-rich iron solutions. All analysis results showed within cellular 36-h reproduction period, the production of only schwertmannite was examined in iron solutions at the Cl−/SO4 2− molar ratios of 0–10 and pH 3.0 ± 0.1. There were differences in two typical morphologies of “pincushions” (Cl−/SO4 2− = 0 and 3) and “hedge-hogs” (Cl−/SO4 2− = 6 and 10) for the schwertmannite nanostructures. And all final schwertmannite particles had the chemical formulas of Fe8O8(OH)8−2x (SO4) x (1.08 ≤ x ≤ 1.66), especially as Cl−/SO4 2− = 0, the visible “pincushions” only being the outermost sections of the whole needles existing in a tightly spherical assemblage of schwertmannite. Moreover, the absence of ferrihydrite and goethite was determined in the nanodimension of these needles, though the initial Fe and SO4 2− were 5600 and of 9600 µg/mL, respectively. It could be induced by the amounts and activities of aqueous Fe, SO4 2−, and Cl− associated with cellular activities and mineral precipitation. This study will be useful for understanding the actual occurrence of iron oxyhydroxide nanostructure and better developing its potential environmental application.