Abstract
Ultrasound is used in various applications, and a frequency between 20 kHz and 2 MHz is mainly used in chemical process. In general, the maximum sonochemical effect caused by cavitation has been observed around 300 kHz, and sonochemical efficiency value (SE_<KI>) has been proposed. In our previous study, the effects of frequency on methylene blue degradation have been investigated, and simple model for estimating the apparent degradation rate constant is proposed. Threshold power is required for degradation to progress, and frequency has less influence on threshold power. However, the effects of frequency and reactant on threshold power have not been investigated. In this study, the effects of frequency on threshold power of KI oxidation and methylene blue degradation were investigated. When ultrasound was irradiated into aqueous KI solution, the generation rate of I_3^- ion was influenced by frequency, and the maximum rate has been observed at 490 kHz. It is also observed that a threshold ultrasonic power is existed for oxidation to progress. The threshold power of KI oxidation increases with increasing frequency. However, the frequency has less influence on threshold power in the case of methylene blue degradation. It is guessed that the pyrolysis of methylene blue occurs in a high frequency region, because the threshold power does not increase with increasing frequency.
