Electron Transfer Processes Between Hydroquinone and Iron Oxides

Abstract

Abstract-The kinetics of hydroquinone oxidation by aqueous suspensions of pure hematite and goethiteferrihydrite mixtures at pH 6.0, 7.4, and 9 was studied using an on-line analysis system. The electron transfer between hydroquinone and the Fe oxides was monitored by UV-visible and electron spin resonance spectroscopy. The adsorption of organics on the Fe oxide surface was detected by Fourier-transform infrared spectroscopy. For different Fe oxides, a higher surface area was correlated with a greater oxidizing ability and greater adsorption of organics, suggesting that the oxidation reaction was a surface process. A reversal of the initially rapid redox reaction was found in this system, suggesting a delayed release of Fe E § into solution as the reduction of the Fe oxide proceeded. Redox potential calculations confirmed the thermodynamic favorability of the reaction reversal. A distribution of the reduced state over neighboring Fe atoms on the oxide surface probably was responsible for the initial suppression of Fe 2+ release into the aqueous phase. Based upon these observations and detection of the semiquinone radical as an intermediate of hydroquinone oxidation, an inner-sphere one-electron transfer mechanism for the oxidation of hydroquinone at the oxide surface is proposed.

Reductive dissolution of arsenic-bearing ferrihydrite

“…The reactivity of iron oxides has been quantified previously by measuring the kinetics of reductive dissolution using hydroquinone and monitoring the formation of benzoquinone (Kung and McBride, 1988;LaKind and Stone, 1989;Anschutz and Penn, 2005;Jentzsch and Penn, 2006). Experiments were performed in duplicate or triplicate and in an anaerobic chamber (Coy Laboratories, 5% H 2 /95% N 2 ) with the pH buffered using 40 mM acetate (pH 3.75, acetic acid (Mallinckrodt) and sodium hydroxide (Mallinckrodt) in Milli-Q water).…”

Coordination Complexes of p-Hydroxybenzoate On Fe Oxides

“…Hematite was prepared by a method similar to that described by Kung and McBride (1988b). Two separate preparations (labeled A and B) were used in this study.…”

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

“…This is unsurprising since previous results have demonstrated that ferrihydrite is substantially more reactive than more crystalline iron oxides ͑i.e., goethite, hematite, etc.͒, and this was attributed to differences in crystallinity. 7,9,[28][29][30][31] Thus, 100-fold greater reactivity observed for ferrihydrite versus goethite is most likely due to a combination of greater crystallinity and larger size of the goethite particles in comparison to the ferrihydrite particles.…”

“…37,38 A number of researchers have studied the reduction of iron oxides by quinones and results show they can effectively be used to quantitatively evaluate the reactivity of these particles. 28,[39][40][41][42] …”