Does -Butyl Alcohol Really Terminate the Oxidative Activity of OH in Inorganic Redox Chemistry?

The hydroxyl radical, OH, is one of the most reactive free radicals and plays significant roles in the oxidative degradation of organic pollutants and the electron transfer of inorganic ions in natural and engineered environmental processes. To quantitatively determine the contribution of OH to oxidative reactions, a specific scavenger, such as -butyl alcohol (TBA), is usually added to eliminate OH effects. Although TBA is commonly assumed to transform OH into oxidatively inert products, this study demonstrates that utilizing TBA as an OH scavenger generates the secondary peroxyl radical (ROO), influencing the oxidation of transition metals, such as Mn. Although ROO is less reactive than OH, it has an extended half-life and a longer diffusion distance that enables more redox reactions, such as the oxidation of Mn(aq) to Mn oxide solids. In addition to promoting Mn(aq) oxidation kinetics, TBA can also affect the crystalline phases, oxidation states, and morphologies of Mn oxide solids. Thus, the oxidative roles of OH in aqueous redox reactions cannot be examined simply by adding TBA: the effects of secondary ROO must also be considered. This study urges a closer look at the potential formation of secondary radicals during scavenged oxidative reactions in environmental systems.