The Role of Iron Coordination in the Production of Reactive Oxidants from Ferrous Iron Oxidation by Oxygen and Hydrogen Peroxide

A new picture of the Fenton reaction has emerged over the last two decades that extends our understanding beyond the acidic conditions studied previously. In the absence of ligands, the reaction produces hydroxyl radical under acidic conditions and a less reactive oxidant, presumed to be the ferryl ion (Fe[IV]), at circumneutral pH values. Formation of complexes between Fe(II) and organic ligands alters the reaction mechanism, resulting in production of hydroxyl radical over a wide pH range. As a result, iron coordination and pH determine the oxidants produced by the Fenton reaction. Consideration of the reactive oxidant produced by the Fenton reaction under environmentally- and biologically-relevant conditions is necessary to develop more effective treatment systems, to predict the fate of iron and carbon in natural waters, and to assess iron-mediated oxidative damage.