Mechanism of improving the rate of sono-oxidation of a KI solution by introduction of CO 2 into an Ar atmosphere.

The rate of sono-oxidation of KI increased in a CO2 -Ar system compared to Ar alone. Higher values were obtained at 200 kHz with a maximum ratio of about forty. To determine the role of additional CO2 in the system, the effect of the pH of the reactant solution, the additional effect of NaHCO3 , sonoluminescence, and an analysis of products were examined. It appeared that the pH was not a significant contributor to the acceleration of sono-oxidation activity although the rate depended on the pH. On the other hand, in spite of the alkaline solution, the reaction rate in NaHCO3 -KI solution was higher than that in the solution without NaHCO3 . This behavior was similar to the case of introduction of CO2 , implying the possible evolution of CO2 from NaHCO3 . Our data suggested that CO2 reacted with H radicals, which were produced together with OH radicals during sonication and a considerable amount of OH radicals remained. Because OH radicals have strong oxidative power, the level of sono-oxidation activity increases.