Rapid As(III) oxidation mediated by activated carbons: Reactive species vs. direct oxidation

Activated carbon (AC) is widely used in pollutant removal, due to its adsorption capacity, conductivity and catalytic performance. However, few studies focus on the redox activity of AC and its role in pollutant transformation. In this study, we found that AC could efficiently mediate the oxidation of As(III) and the process of As(III) oxidation was pH and oxygen concentration dependent. In general, the presence of O₂ promoted As(III) oxidation at pH 3.0-9.5. Acidic and alkaline conditions favored As(III) oxidation regardless of whether there was oxygen, but the mechanisms involved were quite different when there was oxygen. At pH 3.0, reactive species (H₂O₂ and ·OH) were generated and accounted for As(III) oxidation; at pH 9.5, As(III) was directly oxidized by O₂ (electron transfer from As(III) to O₂ mediated by carbon matrix) under aerobic conditions. Pre-oxidation and cyclic experiments results indicated the ability of AC to oxidize As(III) at pH 9.5 was sustainable and recyclable. This study provided a new insight in pollutant oxidation by AC in the environment.