Reduction of crystalline iron(III) oxyhydroxides using hydroquinone: Influence of phase and particle size

Abstract

Iron oxides and oxyhydroxides are common and important materials in the environment, and they strongly impact the biogeochemical cycle of iron and other species at the Earth's surface. These materials commonly occur as nanoparticles in the 3 -10 nm size range. This paper presents quantitative results demonstrating that iron oxide reactivity is particle size dependent. The rate and extent of the reductive dissolution of iron oxyhydroxide nanoparticles by hydroquinone in batch experiments were measured as a function of particle identity, particle loading, and hydroquinone concentration. Rates were normalized to surface areas determined by both transmission electron microscopy and Braunauer-Emmett-Teller surface. Results show that surface-area-normalized rates of reductive dissolution are fastest ͑by as much as 100 times͒ in experiments using six-line ferrihydrite versus goethite. Furthermore, the surface-area-normalized rates for 4 nm ferrihydrite nanoparticles are up to 20 times faster than the rates for 6 nm ferrihydrite nanoparticles, and the surface-area-normalized rates for 5 ϫ 64 nm goethite nanoparticles are up to two times faster than the rates for 22ϫ 367 nm goethite nanoparticles.

The importance of shallow hydrothermal island arc systems in ocean biogeochemistry

“…A highly variable portion (9.7–82.2%), but typically about 5 nM, of DFe occurred as “labile” Fe (see section ; Figure ), indicating that some Fe was bound to weak organic ligands (log K´ FeL < 23) or weakly crystalline mineral phases [ Hawkes et al ., ]. This “labile” portion was unrelated to the total Fe concentration, probably indicating a variable degree of crystallinity and reactivity of Fe‐oxyhydroxide and ligand phases [ Anschutz and Penn , ]. Iron‐rich particles were pervasive at both hydrothermal and mid‐caldera stations, and the fractions of oxyanions P Ox , V Ox and As Ox, and Mn covaried with Fe in the particles in ratios 0.41, 0.0046, 0.0013, and 0.16, respectively (Table ).…”

Factors modifying the structural configuration of oxyanions and organic acids adsorbed on iron (hydr)oxides in soils. A review

“…Thermodynamically unstable reduced compounds and minerals are rapidly oxidized upon contacting the atmosphere, and iron 3+ oxide is formed (Takahashil et al 1999;Cornell and Schwertmann 2003). However, a very distinctive phenomenon observed between the converted field and the upland field is the size of iron 3+ oxide particles in the soil profile (Schwertmann 1993;Anschutz and Penn 2005). The precipitation during the reconstructive transformation determines the size of iron (hydr)oxides, and newly precipitated iron 3+ oxide is found to be nanosized.…”

Facet‐Mediated Photodegradation of Organic Dye over Hematite Architectures by Visible Light

“…To explore the intrinsic photoreactivity, k was normalized to the specific surface area (Table 1), referred to k s 44. 48 Table 1 illustrates that at equivalent mass loadings, α‐Fe 2 O 3 nanorods exhibit the greatest photoreactivity with k s =3.06×10 −3 min −1 L m −2 , while k s is 2.72×10 −3 and 7.28×10 −4 min −1 L m −2 for nanocubes and nanoplates, respectively. The photonic efficiency ξ , which is defined as the ratio of the dye degradation rate and the incident photon flux at a given wavelength, is calculated according to Equation (1):49 …”