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.

Reductive Dissolution and Reactivity of Ferric (Hydr)oxides: New Insights and Implications for Environmental Redox Processes

“…The difference between rates for 5 × 64 nm goethite nanoparticles was up to two times faster than for 22 × 367 nm goethite nanoparticles [59]. But still surface area-normalized rates differed between the ferrihydrite and the goethite nanoparticles by a factor of 100.…”

Interpreting nanoscale size-effects in aggregated Fe-oxide suspensions: Reaction of Fe(II) with Goethite

“…Although their reactivity is sometimes attributed to very high specific surface areas, recent experimental evidence indicates that iron oxide nanoparticles may display reactive properties that cannot be extrapolated to the behavior of larger materials simply on the basis of surface area differences. These investigations have focused on common iron oxides such as goethite, ferrihydrite and hematite and have reported enhanced nanoparticle reactivity with respect to interfacial processes such as cation adsorption, electron transfer and oxide dissolution (Anschutz and Penn, 2005;Madden and Hochella, 2005;Madden et al, 2006). Such behavior could result from a greater density of reactive sites per unit surface area on nanoparticle surfaces, or greater inherent reactivity of nanoparticle surface sites relative to sites on larger particles (Tratnyek and Johnson, 2006).…”

Electron tunneling properties of outer-membrane decaheme cytochromes from Shewanella oneidensis

“…In the case of shuttles, it is possible that outer-membrane cytochromes donate electrons to biosynthetic shuttle molecules such as quinones, which then transfer electrons to specific sites on the oxide surface (Newman and Kolter, 2000;Lies et al, 2005). Reduction of hematite (a-Fe 2 O 3 ) surfaces by hydroquinone molecules appears to be a relatively facile process (Stack et al, 2004;Anschutz and Penn, 2005) despite the dramatic influence of adsorption, pH, and quinone structure on the thermodynamics of such reactions (Uchimiya and Stone, 2006). Reductive dissolution features on hematite surfaces observed at locations not associated with specific cell attachment sties of S. putrefaciens CN32 may also support this pathway.…”