Polycrystallinity of green rust minerals and their synthetic analogs: Implications for particle formation and reactivity in complex systems

Abstract

We demonstrate in this study that natural green rust nanoparticles and their synthetic analogs can be complex polycrystalline phases composed of crystallites only a few nanometers in size, and they often include nanometer-sized regions of amorphous material. The natural green rusts are Zn-bearing pseudo-hexagonal platelets previously identified by us in the contaminated mine drainage of the former Ronneburg uranium mine in Germany (Johnson et al. 2014). We also identified Ni-and Cubearing green rust platelets in the sediment underlying the drainage outflow 20 m downstream, and, using dark-field transmission electron microscopy (DF-TEM), found that these natural green rusts are not usually structurally coherent single crystals. Synthetic sulfate green rusts are also polycrystalline and composed of crystallites of only a few nanometers in size, though different synthesis conditions produced different patterns of polycrystallinity. While pseudo-hexagonal platelets are the typical morphology of green rust, we also synthesized green rust nanorods, which have not previously been reported. In addition to the known characteristics of green rusts (including a very large aspect ratio and surface area to volume ratio, and the redox properties allowed by the structural mixture of Fe 2+ and Fe 3+ ), these polycrystalline platelets exhibit a high abundance of defect sites and likely a rough surface topography. The combination of these characteristics has important implications for the reactivity of green rust with biogeochemical interfaces in natural and anthropogenic systems.

Outdoor urban nanomaterials: The emergence of a new, integrated, and critical field of study

“…More interestingly, Figure 3g shows an aggregate of pseudo-hexagonal platelets. These NMs have minor sulfur content with d-spacings of 2.49 Å and 1.46 Å, which is very close to that expected for green rust (Fe 2 (OH,SO 4 ) 4.88 (Johnson et al, 2015).Given the specific morphology and element composition (Christiansen et al, 2009;Johnson et al, 2014;Wankel et al, 2012), this green rust most likely formed in a reduced environment in the stormwater pond, which is consistent with iron sulfide NMs also found in the sediment of this pond. Green rust platelets are known to be very unstable under oxic conditions, which helps explain why they are rarely observed although they are thought to be relatively common.…”

Order and Disorder in Layered Double Hydroxides: Lessons Learned from the Green Rust Sulphate - Nikischerite Series.

“…Such a radius of curvature would mean that the average particle, if composed of a domain as wide as the particles, would have to curl back on itself to produce a nanotube. Although GR has been observed to form nanotubes, 49 we did not observe them in these experiments. Thus, particle curvature cannot explain the observed decrease in structural coherence within the metal hydroxide sheet.…”

Vivianite formation in ferruginous sediments from Lake Towuti, Indonesia

“…Detection limit of the method is 0.05 µM. Mn 2+ concentrations were analyzed spectrophotometrically as previously published (Jones et al, 2011 and, following the formaldoxime method (Brewer and Spencer, 1971). Pore water Ca 2+ , Mg 2+ and SO 2− 4 concentrations were analyzed via normal and suppressed ion chromatography, as previously described (Vuillemin et al, 2016).…”