Free Radical and Free Atom Reaction in the Sonolysis of Aqueous Iodide and Formate Solutions

Article abstract of DOI:10.1021/j100266a038

Solutions of potassium iodide and sodium formate were irradiated with 300-kHz ultrasound and the products analyzed.The irradiations were carried out under atmospheres of argon, oxygen, and argon-oxygen mixtures of varying composition.In addition, experiments with pure water and water containing ozone were undertaken.The products of irradiation of iodide solutions are iodine and hydrogen peroxide; hydrogen is also formed in the absence of oxygen.With an atmosphere of 70percent argon and 30percent oxygen, the yields are drastically higher than for irradiation under puer argon or oxygen.The products of the irradiation of formate solutions are hydrogen, carbon dioxide, hydrogen peroxide, and oxalate in the absence of O2 and hydrogen peroxide and carbon dioxide in the presence of O2.A strong enhancement of the yields is also observed for formate solutions containing both argon and oxygen.Ozone could not be identified as a stable product of the irradiation of oxygenated water.On the contrary, water containing ozone was found to rapidly lose O3 upon ultrasonic irradiation.The dependence of the yields of the various products on the concentration of the dissolved substances was studied in order to derive a mechanism of the chemical action of ultrasound.The results are explained in terms of the formation of H and OH radicals in the gas bubbles.In the absence of oxygen, the H atoms form H2 and the OH radicals form hydrogen peroxide or react with nonvolatile substrates in the interfacial region.In the presence of oxygen, HO2 radicals, OH radicals, and O atoms are formed.The HO2 radicals do not attack iodide or formate but produce hydrogen peroxide.Oxygen atoms are scavenged by iodide and formate ions.An appreciable concentration of the superoxide radical anion, O2(1-), was detected after the irradiation of an oxygenated, 1E-2 M formate solution of pH 14.The O2(1-) anion decayed after irradiation with half-life of 3 min.