Structural investigations of synthetic ferrihydrite nanoparticles doped with Si

The influence of silicate on transformation pathways of synthetic 2-line ferrihydrite

“…Increasing silicon content results in a gradual broadening and a shift of the former toward lower two-theta angles. Similar features, observed for both synthetic [17,18,27] and natural [16,41,49] Si-ferrihydrites, indicate reducing crystallinity and/or lowering crystal size.…”

“…These ambiguous results might result from the character of the observed objects-Cismasu et al [17] noted the decrease in individual ferrihydrite particle sizes, but the oxyhydroxide aggregates appeared more compact. Hence, Seehra et al [27] might observe ferrihydrite aggregates rather than single crystallites. The character of silica association with ferrihydrite depends on Si/Fe molar ratio-at low values, monomeric silicate is adsorbed on the ferrihydrite surface, whereas the high ratio promotes polymerizing of silica to form a separate phase [19].…”

“…A decrease in both ferrihydrite particle size and crystallinity with increasing content of Si was found [17]. The opposite observation [27] suggested that enhanced adsorption of silicate ions to the ferrihydrite surface caused the increase in the nanoparticle dimensions. These ambiguous results might result from the character of the observed objects-Cismasu et al [17] noted the decrease in individual ferrihydrite particle sizes, but the oxyhydroxide aggregates appeared more compact.…”

“…These ions affect ferrihydrite composition, surface chemistry, reactivity and sorption properties [14,[17][18][19][20][21][22]. Silicate, the most important impurity, lowers crystallinity of this nanomineral and modifies its morphology, magnetic ordering and solubility [15,[23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39], though the ferrihydrite structure itself is not directly altered [30]. Reducing crystallinity has been thought to result from the formation of soluble Fe-Si complexes during the oxyhydroxide precipitation.…”

Silicon-Rich, Iron Oxide Microtubular Sheath Produced by an Iron-Oxidizing Bacterium, Leptothrix sp. Strain OUMS1, in Culture

“…Although Carlson and Schwertmann [29] noted that Si-O-Fe bonds were probably responsible for stability of natural ferrihydrite which always contained some silica, the role of Si in Fe/Si complex in abiotic system has not been well understood. Because the crystallinity of synthetic 2Fh is lowered when the structure is doped with Si [30][31][32], the Si-dependent changes of the texture found in the present study may not directly be associated with the existence of OUMS1, but result from direct autocatalytic oxidation, chemical/physical interactions, among elements. Referring the earlier paper [33] that organics were responsible for the poor crystallinity of microbe-associated Fe minerals, the crystallinity change observed in this study could be dependent on not only Si but also the bacterial organics.…”