Decomposition of ozone in water: rate of initiation by hydroxide ions and hydrogen peroxide

The initiation of ozone decomposition in "pure water" is first order in O3 and OH- concentration and kO3,OH- becomes 70 ± 7 M-1 s-1 when a sequence of reactions is assumed by which three molecules of O3 are eliminated per primary event. The difference between this value and higher values reported in the earlier literature may be explained by interferences by radical chain reactions which have not been totally inhibited in those studies. H2O2 also reacts with O3 when present as an anion, HO2-. kO3,OH- is (2.8 ± 0.5) × 106 M-1 s-1 when it is assumed that 'two molecules of O3 are eliminated per primary event. Therefore, whenever H2O2 > 10-7 M (pH 2- has a greater effect than OH- on the decomposition rate of O3 in water. The high reactivity of HO2- explains that H2O2 is observed as a significant intermediate in the ozonated water only if the pH is low, e.g., <6.