Catalytic generation of hydroxyl radicals by dioxygen-mediated oxidation of p-aminophenol by simple cobalt(ii) ions in bicarbonate aqueous solution for use in Acid Orange 7 decolorization

Abstract

Dioxygen from air is the cleanest and the most abundant oxidative agent; it is of great significance to activate dioxygen to reactive oxygen species for environmental pollutant transformation and degradation. In this work, the simple cobalt(II) ion was found to exhibit high efficiency for p-aminophenol oxidation in bicarbonate aqueous solution with dioxygen as the oxidant at room temperature; simultaneously, the azo dye, Acid Orange 7, can be decolorized by the system. The formed reactive species was carefully studied by electron spin resonance and spin-trapping technologies and radical scavenging measurements. The metal-bound hydroxyl radical, which originated from a Fenton-like reaction between the Co²⁺–HCO₃⁻ complex and the intermediate of H₂O₂, was suggested as the main reactive species. This study can provide new insight into the mechanism of the molecular oxygen activation by simple metal complexes and their application to the removal or transformation of pollutants under mild reaction conditions.