Mechanism of improving the rate of sono-oxidation of a KI solution by introduction of CO2 into an Ar atmosphere

Abstract

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.