Sonochemical degradation of chlorophenols in water

Sonochemical degradation of dilute aqueous solutions of 2-, 3- and 4-chloro phenol and pentachlorophenol has been investigated under air or argon atmos phere. The degradation follows first-order kinetics in the initial state wi th rates in the range 4.5-6.6 mu M min(-1) under air and 6.0-7.2 mu M min(- 1) under argon at a concentration of 100 mu M of chlorophenols. The rate of OH radical formation from water is 19.8 mu M min(-1) under argon and 14.7 mu M min(-1) under air in the same sonolysis conditions. The sonolysis of c hlorophenols is effectively inhibited, but not completely, by the addition of t-BuOH, which is known to be an efficient OH radical scavenger in aqueou s sonolysis. This suggests that the main degradation of chlorophenols proce eds via reaction with OH radicals; a thermal reaction also occurs, although its contribution is small. The addition of appropriate amounts of Fe(II) i ons accelerates the degradation. This is probably due to the regeneration o f OH radicals from hydrogen peroxide, which would be formed from recombinat ion of OH radicals and which may contribute a little to the degradation. Th e ability to inhibit bacterial multiplication of pentachlorophenol decrease s with ultrasonic irradiation. (C) 2000 Elsevier Science B.V. All rights re served.