Powdered activated carbon-catalyzed chlorine oxidation of bisphenol-A and methylene blue: Identification of the free radical and effect of the carbon surface functional group

Abstract

The effect of powdered activated carbon (PAC) on chlorine oxidation is not well understood, therefore this study was designed to further investigate the chlorine oxidation mechanism with the presence of PAC. The oxidation processes of two model organic pollutants (bisphenol-A and methylene blue) with chlorine were compared in the absence and presence of PAC. The results showed a significant increase in reaction rates with the addition of PAC. Electron spin resonance indicated that the PAC catalyzed the oxidation of chlorine to generate more Cl and O2−. Additionally, the analysis of the surface characteristics of thermally modified PACs under N2 and their corresponding reaction rates revealed that there existed a significant correlation between the CO groups and the catalytic effect. PAC exhibited a much lower reaction rate under H2 modification, which indicated that the π electrons of the basal plane might be involved in the catalysis. Density functional theory calculations confirmed that the various oxygen groups on PAC reduced the activation barrier for HOCl dissociation, particularly the carboxyl group. This investigation provides a better understanding of the interactions between chlorine and activated carbon materials, which could be useful for selecting suitable water treatment agents.