Probing the radical chemistry and the reaction zone during the sono-degradation of endocrine disruptor 2-phenoxyethanol in water

Abstract

Sonochemical degradation at 600 kHz of 2-phenoxyethanol (PhE), an endocrine disrupting compound, was performed in the presence of several organic additives, namely: 2-propanol, Triton X-100 and sucrose, of different volatilities to obtain detailed information on the reaction zone and the oxidation pathway of this priority emerging water contaminate. It was found that sonication at 600 kHz and 120 W completely remove PhE (10 mg L−1) from aerated solutions within 100 min of irradiation. Very little removal of PhE (∼7%) and low accumulation of H2O2 took place in the presence of adequate amount of 2-propanol, indicating that reaction with OH radical outside the bubble is the major degradation pathway of PhE. Addition of the hydrophobic surfactant Triton X-100, as an OH-probe for the interfacial region, at 10 and 100 mM reduced the degradation event by 57% and 72% and resulted in more than 50% decrease in the yield of H2O2, confirming that PhE degradation occurs mainly at the bubble/solution interface with hydroxyl radical attack. Addition of the hydrophilic substrate glucose at high doses decreased slightly (∼7%) the degradation of PhE and the formation rate of H2O2, meaning that the bulk of the solution participate marginally in the degradation of the pollutant. Finally, analyzing the degradation rates at various initial PhE concentrations (2–400 mg L−1) with a heterogeneous Langmuir type mechanism underlined the predominance of interfacial radical reactions during the oxidation of PhE, particularly at high initial pollutant concentrations.