In this presentation, we report influences of concentration of KI and frequency on the rate of sono-oxidation in a CO2-Ar atmosphere. Sonication was performed using an ultrasonic irradiator (Shinka, ...200 kHz, 100 W and Honda, 2.4 MHz, 15 W) at 25 ℃. The rate of sono-oxidation was evaluated by KI dosimetry using UV-Vis spectrophotometer (JASCO V-650, measuring wavelength is 355 nm). The rate difference between with and without CO2 in an Ar atmosphere was indicated as Improvement index. The index means the ratio of absorbance in a CO2-Ar atmosphere to that in Ar atmosphere. Sono-oxidation rate of NaI solution increased by introduction of CO2 as same as KI. The Improvement index increased with decreasing KI concentration not only at 200 kHz but also at 2.4 MHz.
In previous paper, we demonstrated the rate of sono-oxidation increased with the introduction of a small amount of CO2. In this presentation, we report influences of concentration of KI and ...sonication time on the rate of sono-oxidation in a CO2-Ar atmosphere. Sonication was performed using an ultrasonic irradiator (shinka, 200 kHz, 100 W) for 25 ℃. The rate of sono-oxidation was evaluated by potassium iodide (0.01 M KI) dosimetry using UV-Vis spectrophotometer (JASCO V-650, measuring wavelength is 355 nm). The rate difference between with and without CO2 in an Ar atmosphere indicates Improvement index, which means the ratio of absorbance in a CO2-Ar atmosphere to that in Ar atmosphere. The Improvement index increased with decreasing KI concentration. Maximum Improvement index was recorded about 9 times at 0.01 M after 30 min sonication. Influence of sonication time on Improvement index, on the other hand, we got about 40 times at 0.01 M after 1.5 hours sonication.
A sonochemical reaction depends on the kind of gas dissolved in the reaction field, namely, in the reactant solution. In former paper, we reported an improvement of sono oxidation rate of KI solution ...in a CO2-Ar system. To study the effect of CO2 existing under alkaline condition, sonication was performed in a NaHCO3-KI solution. Sonication was carried out in a system with a 200 kHz transducer (KAIJO, QUAVA mini QR003, 50 W). The reactants comprised several concentrations of KI aqueou s solution. Before sonication, the reactor was filled with Ar gas and a certain amount of NaHCO3 was dosed to the solution. Sono-oxidation rate was evaluated by KI dosimetry (λmax = 355 nm, JASCO V730). In the cases of no addition of NaHCO3 a weak absorbance, namely, a slow rate of sono oxidation was observed. On the other hand, in spite of the alkaline solution, the system with dissolved NaHCO3 had the highe st absorbance We considered sono oxidation activity would be enhanced by CO2 produced from NaHCO3. However, effect of KI concentration on sono-oxidation rate in NaHCO3-KI system was different from that in CO2-Ar system.
In the previous presentation, we concluded that dilute NaHCO3-KI solution had moresono-oxidation rate compared with the KI solution without NaHCO3 under Argon (Ar) atmosphere using 200kHz ultrasonic ...generator. In this presentation, to confirm the previous results we carried out sonolysis of 0.1 MKI-NaHCO3 solution under high frequency using by an ultrasonic generator (Honda Electronics HM-303, 2.4MHz and maximum power 15 W). The rate of sono-oxidation was evaluated by potassium iodide (KI)dosimetry at 355 nm using UV-Vis spectrophotometer (JASCO V-650 and V-730).We also observed multi-bubble sonoluminescence (MBSL) of NaHCO3 solution. The intensity of MBSL felldown with concentration of NaHCO3. Namely, cavitation intensity decreases in the presence of NaHCO3. Asyou know, NaHCO3 reacts to CO2 during sonication and the temperature in bubbles fall down by CO2. The rateof sono-oxidation, however, increased in the solution with a small amount of NaHCO3. It has been known thatCO2 quenches •H radicals, which are produced from solvent (H2O). Remaining •OH radicals oxidize I-.Therefore, increasing rate of sono-oxidation by adding NaHCO3 in an aqueous solution was confirmed notonly at 200 kHz but also at 2.4 MHz ultrasonic atomizer.
Sonolysis of 0.1MKI-NaHCO_3 solution was carried out under Ar by an ultrasonic extraction apparatus (Honda Electronics UMS, 200 kHz and maximum power 15 W). The rate of sono-oxidation was evaluated ...by potassium iodide (KI) dosimetry at 355 nm using UV-Vis spectrophotometer (JASCO V-650). We had more rate below 1.5 mM NaHCO_3-KI solution compared with the KI solution without NaHCO_3. Over 1.5 mM solution of NaHCO_3, on the contrary, the rate fell down. Thus, sono-oxidation rate of I^- depended on concentration of NaHCO_3. We also observed multi-bubble sonoluminescence (MBSL) of NaHCO_3 solution. The intensity of MBSL fell down with concentration of NaHCO_3. Namely, cavitation intensity decreases in the presence of NaHCO_3 because NaHCO_3 reacts to CO_2 during sonication and the temperature in bubbles fall down by CO_2. The rate of sono-oxidation, however, increased in the solution with a small amount of NaHCO_3. It has been known that CO_2 quenches ^.H radicals, which are produced from solvent (H_2O). Remaining ^.OH radicals oxidize I^-. Therefore, NaHCO_3 in an aqueous solution could play the role of rate control of sono-oxidation under ultrasonic irradiation.
