Determination of Rate Constants for Ozonation of Ofloxacin in Aqueous Solution

Abstract

The ozonation of the quinolone antibiotic ofloxacin in water has been investigated with focus on kinetic parameters determination. The apparent stoichiometric factor and the second-order rate constants of the reactions of ozone and hydroxyl radical with ofloxacin were determined at 20 °C in the pH range of 4–9. The apparent stoichiometric factor was found to be about 2.5 mol O3/mol ofloxacin regardless of the pH. The rate constant of the reaction between ozone and ofloxacin was determined by a competitive method (pH = 6–9) and a direct ozonation method (pH = 4). It was found that this rate constant increases with pH due to the dissociation of ofloxacin in water. The direct rate constants of ofloxacin species were determined to be 1.0 × 102, 4.3 × 104 and 3.7 × 107 for cationic, neutral-zwitterion and anionic species, respectively. Accordingly, the attack of ozone to ofloxacin mainly takes place at the tertiary amine group of the piperazine ring, though some reactivity is also due to the quinolone structure and oxazine substituent. The rate constant of the reaction between ofloxacin and hydroxyl radical was obtained from UV/H2O2 photodegradation experiments. It was found that this rate constant varies with pH from 3.2 × 109 at pH 4 to 5.1 × 109 at pH 9.