Dynamics of interfacial charge transfer in iron(III) oxide colloids

Mulvaney, Paul; Swayambunathan, V.; Grieser, Franz; Meisel, Dan

doi:10.1021/j100334a049

Cited by 36 publications

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“…In these control experiments, there was no measurable shift in the soluble viologen concentration before and after the addition of the oxide, indicating that no sorption was occurring. Similar observations have been made in previous studies which used viologen and iron oxides(149,157,159). In all experiments, the amount of viologen added to a reactor was known, allowing for comparison between the theoretical and experimental total viologen concentrations; the viologen concentration was typically within 10 % of the expected value, with no bias in either direction (i.e., no consistent over-or under-estimation)(Tables 5.1-5.3).…”

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confidence: 66%

“…Previous work in the field of photochemistry has utilized soluble radical redox probes to determine the redox state of the solution (149,(154)(155)(156)(157)(158)(159). The viologens (4,4'-Bipyridine and its substituents) are commonly used due to their pH-independent oneelectron reversible redox potentials which can be manipulated with functional groups (155,160).…”

Section: Resultsmentioning

confidence: 99%

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Redox behavior of magnetite in the environment

Gorski¹

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Magnetite (Fe 3 O 4) is a commonly found in the environment and can form via several pathways, including biotic and abiotic reduction of Fe 3+ oxides and the oxidation of Fe 2+ and Fe 0. Despite extensive research, the redox behavior of magnetite is poorly understood. In previous work, the extent and kinetics of contaminant reduction by magnetite varied by several orders of magnitude between studies, two fundamentally different models are used to explain magnetite oxidation (i.e., core-shell diffusion and redox-driven), and reported reduction potentials vary by almost 1 V. In other fields of science (e.g., physics), magnetite stoichiometry (x = Fe 2+ /Fe 3+) is a commonly measured property, however, in environmental studies, the stoichiometry is rarely measured. The stoichiometry of magnetite can range from 0.5 (stoichiometric) to 0 (completely oxidized), with intermediate values (0 < x < 0.5) referred to as nonstoichiometric or partially oxidized magnetite. To determine the relationship between magnetite stoichiometry and contaminant fate, the reduction rates of three substituted nitrobenzenes (ArNO 2) were measured. The kinetic rates varied over five orders of magnitude as the particle stoichiometry increased from x = 0.31 to 0.50. Apparent 15 N kinetic isotope effects (15 N-AKIE) values for ArNO 2 were greater than unity for all magnetite stoichiometries investigated, and indicated that mass transfer processes are not controlling the reaction rate. To determine if the reaction kinetics were redox-driven, magnetite open circuit potentials (E OCP) were measured. E OCP values were linearly related to the stoichiometry, with more stoichiometric magnetite having a lower potential, in good agreement with redox-driven models. The reaction of aqueous Fe 2+ and magnetite was investigated. Similar to previous findings for other Fe 3+ oxides, the formation of a stable sorbed Fe 2+ species was not observed; instead, the sorbed Fe 2+ underwent interfacial electron transfer to form a partially oxidized magnetite phase, which was accompanied by reduction of the viii TABLE OF CONTENTS LIST OF TABLES .

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confidence: 66%

Section: Resultsmentioning

confidence: 99%

Redox behavior of magnetite in the environment

Gorski¹

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“…A similar approach was used by Mulvaney et al [44] to study interfacial charge transfer in Fe(III) colloids (hematite and goethite nanoparticles). Instead of AQDS they used radiolytically produced organic radicals.…”

Section: Redox Potential Of Fe(ii) Sorbed To Ferric Hydroxidesmentioning

confidence: 99%

“…It appeared that the rate of electron transfer is governed by the free energy difference between the redox potential of the redox couple in the electrolyte and the flatband potential in the solid as was demonstrated in radiolysis experiments with colloidal ferric oxides, that is, experiments where free radicals are produced to allow for electron transfer [44]. In these experiments, it was clearly demonstrated that aside from the quasi Fermi level, also the electrostatic interaction between the reducing radical and the electric double layer at the interface influenced electron transfer.…”

Section: The Semiconducting Properties Of Ferric (Hydr)oxidesmentioning

confidence: 99%

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

Peiffer

Wan

2016

Iron Oxides

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“…23 Earlier studies of iron oxide reduction using pulse radiolysis concluded that electron migration could cause indefinite trapping of electrons. 24 Thus, internal electron conduction could contribute to the overall reaction rates of iron oxide dissolution or recrystallization, but this contribution has never been quantified.…”

Section: ■ Introductionmentioning

confidence: 99%

Electron Mobility and Trapping in Ferrihydrite Nanoparticles

Soltis

Schwartzberg²,

Zarzycki

et al. 2017

ACS Earth Space Chem.

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Iron is the most abundant transition metal in the Earth's crust, and naturally occurring iron oxide minerals play a commanding role in environmental redox reactions. Although iron oxide redox reactions are well-studied, their precise mechanisms are not fully understood. Recent work has shown that these involve electron transfer pathways within the solid, suggesting that overall reaction rates could be dependent upon electron mobility. Initial ultrafast spectroscopy studies of iron oxide nanoparticles sensitized by fluorescein derivatives supported a model for electron mobility based on polaronic hopping of electron charge carriers between iron sites, but the constitutive relationships between hopping mobilities and interfacial charge transfer processes has remained obscured. We developed a coarse-grained lattice Monte Carlo model to simulate the collective mobilities and lifetimes of these photoinjected electrons with respect to recombination with adsorbed dye molecules for essential nanophase ferrihydrite and tested predictions made by the simulations using pump−probe spectroscopy. We acquired optical transient absorption spectra as a function of the particle size and under a variety of solution conditions and used cryogenic transmission electron microscopy to determine the aggregation state of the nanoparticles. We observed biphasic electron recombination kinetics over time scales that spanned from picoseconds to microseconds, the slower regime of which was fit with a stretched exponential decay function. The recombination rates were weakly affected by the nanoparticle size and aggregation state, suspension pH, and injection of multiple electrons per nanoparticle. We conclude that electron mobility indeed limits the rate of interfacial electron transfer in these systems, with the slowest processes relating to escape from deep traps, the presence of which outweighs the influence of environmental factors, such as pH-dependent surface charge.

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Dynamics of interfacial charge transfer in iron(III) oxide colloids

Cited by 36 publications

References 0 publications

Redox behavior of magnetite in the environment

Redox behavior of magnetite in the environment

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

Electron Mobility and Trapping in Ferrihydrite Nanoparticles

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