Kinetic of benzotriazole oxidation by ozone and hydroxyl radical

Ozonation experiments were performed in batch reactors in order to determine the rate constants for the reaction of molecular ozone and OH radicals with benzotriazole (BT) at different pHs. The first group of ozonation experiments was carried out for the determination of the rate constant for the direct reactions between ozone and BT. Two different kinetic models were used for the determination of kinetic rate constants: (i) the log-reduction of BT with ozone in excess, (ii) the competition kinetic model. The second-order rate constants for BT with molecular ozone were determined to be 36.4 ± 3.8 M⁻¹ s⁻¹ and 18.4 ± 0.8 M⁻¹ s⁻¹ at pH 2 from the two methods respectively. With the competition method, the value at pH 5 was found to be 22.0 ± 2.0 M⁻¹ s⁻¹. In a following stage, the reaction of BT with OH radicals was investigated at pH values ranging from 2 to 10.2. Using a method involving two probe compounds during the ozonation, the second-order rate constants of the BT reaction with hydroxyl radicals were determined. The rate constants were found to vary from 6.2 × 10⁹ M⁻¹ s⁻¹ at pH 10.2 to 1.7 × 10¹⁰ M⁻¹ s⁻¹ at pH 2.