Microbial Reduction of Fe(III) in Hematite Nanoparticles by Geobacter sulfurreducens

Abstract

The rates of microbial Fe(III) reduction of three sizes of hematite nanoparticles by Geobacter sulfurreducens were measured under two H2 partial pressures (0.01 and 1 atm) and three pH (7.0, 7.5, and 8.0) conditions. Hematite particles with mean primary particle sizes of 10, 30, and 50 nm were synthesized by a novel aerosol method that allows tight control of the particle size distribution. The mass-normalized reduction rates of the 10 and 30 nm particles were comparable to each other and higher than the rate for the 50 nm particles. However, the surface area-normalized rate was highest for the 30 nm particles. Consistent with a previously published model, the reduction rates are likely to be proportional to the bacteria-hematite contact area and not to the total hematite surface area. Surface area-normalized iron reduction rates were higher than those reported in previous studies, which may be due to the sequestration of Fe(II) through formation of vivianite. Similar initial reduction rates were observed under all pH and H2 conditions studied.

Nanosized Iron Oxide Colloids Strongly Enhance Microbial Iron Reduction

“…Nanosized, colloidal aggregates clearly showed a higher reactivity per unit surface than noncolloidal macroaggregates. The surface-normalized rates of 397 Ϯ 180 nmol/m 2 h ferrous iron production for our nanosized hematite aggregates lay slightly below the range observed by Yan et al of 837 to 2,280 nmol/m 2 h for monocrystalline hematite nanoparticles in a size range of 10 to 50 nm and hydrogen as an electron donor (47). Rates of 2.4 to 22.26 nmol/m 2 h Ϫ1 were reported by Roden and Zachara (41), which corresponds to the reduction rates of the macroaggregates used in our study (Table 1).…”

“…Figure 2 shows that the differences in the surface-normalized reactivities within the various colloidal aggregate species are only minor and do not follow a size-dependent relationship. Even among monocrystalline nanoparticles of Ͻ100 nm, no clear size-reactivity relationship was discovered (5,47). Instead, in our experiments we observed a size dependency of the reduction rate when comparing colloidal, nanosized aggregates to bulk macroaggregates; the difference in the determined biotic reactivity might thus be credited to the suspended state and, therefore, the high spatial bioaccessibility of the colloidal iron oxide aggregate.…”

“…This is striking, since for nanoparticulate aggregates, as used in our study, surface passivation should have even more impact than for discrete particles (47). That study also reported a degree of reduction of up to 17% for hematite nanoparticle reduction, and only a slight degree of reduction was observed when applying Shewanella instead of Geobacter (5).…”

The mineralogic transformation of ferrihydrite induced by heterogeneous reaction with bioreduced anthraquinone disulfonate (AQDS) and the role of phosphate

“…The dissimilatory reduction of numerous Fe(III)-containing subsurface mineral forms have been studied, with recognition that high surface area and high solubility are conducive to bioreduction because of surface chemical and thermodynamic constraints (Roden and Zachara, 1996;Bonneville et al, 2004;Roden, 2006;Yan et al, 2008). The following bioavailability sequence has been observed based on total Fe(III) mass: ferrihydrite $ lepidocrocite > nanocrystalline Fe(III) oxides > Fe(III) containing phyllosilicates (smectite, nontronite, illite) > crystalline Fe(III) oxides (Roden and Zachara, 1996;Kostka et al, 2002;Zachara et al, 2002;Bonneville et al, 2004).…”

Iron-Reducing Bacteria and Iron Nanostructures

“…10, 30, and 50 nm). The mass-normalized reduction rates of particles with 10 and 30 nm diameters were comparable to each other and higher than the rate for the 50 nm particles [46]. IRB are also capable to convert iron ions to iron nanoparticles.…”