Catalytic activation of dioxygen to hydroxyl radical and efficient oxidation of o-aminophenol by cobalt(II) ions in bicarbonate aqueous solution

•Simple Co2+–HCO3− system efficiently oxidized o-aminophenol with O2 as oxidant.•H2O2 was formed from protonation of two electron reduction species of O2.•HO• was generated from H2O2 and contributed to o-aminophenol oxidation.•Possible mechanism for the catalytic performance was proposed.

Increasing attention has been paid to the activation of the ideal oxidant O2 to reactive oxygen species for environmental pollutants transformation and complete degradation. In this work, the oxidation of o-aminophenol (OAP), a poor biodegradable intermediate, by simple Co2+ ions in HCO3− aqueous solution with O2 under ambient conditions was investigated. The results reveal that OAP is efficiently transformed to a less harmful compound 2-aminophenoxazine-3-one (APZ) by the Co2+–HCO3− system. HCO3− is necessary for the reaction by promoting the protonation of the two-electron reduction species of O2 to produce H2O2. The metal-bound hydroxyl radical (•OH) generated from the intermediacy of H2O2 contributes to APZ formation. Based on the analysis of electron spin resonance spin-trapping technologies, radical scavenging measurements and kinetics of APZ formation under different conditions, a possible pathway for •OH radical formation and APZ production is proposed. This study can provide new insight on the mechanism of the molecular oxygen activation by simple metal complexes and their application on pollutant removal under mil reaction conditions.

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