Quantitative prediction of generation of hydroxyl radicals from ozone microbubbles

Abstract

Concentration of hydroxyl radicals generated from ozone microbubbles was determined by using an indirect method over a wide range of pH (i.e. pH 3–10). p-Chlorobenzoic acid (PCBA) was used as the probe compound to calculate the concentration of hydroxyl radicals. A constant, Rct, was defined as the ratio of OH and O3 exposures, which was employed to estimate the concentration of hydroxyl radicals. The effects of pH and carbonate ions on the generation of hydroxyl radicals were studied. It was observed that the O3 exposure and the depletion of PCBA were higher at acidic pH than at the alkaline pH. At acidic pH, CO32− acted as the ·OH scavenger only, whereas at alkaline pH, it inhibited ozone decomposition. This changed the values of ·OH exposure, O3 exposure, and hence, Rct. The degradation of phenol was performed at pH 3–10 by using ozone microbubbles. The contributions of ·OH and O3 on the oxidation of phenol were calculated. A mechanism of the generation of ·OH from the ozone microbubbles under acidic and alkaline conditions was developed.