Methanol Inhibition of Sonochemistry: A Microscopic Investigation of Single Bubble Effects

Due to the sensitivity of the sonochemical production to the different operating conditions, in the present paper, a microscopic investigation is conducted to evaluate the impact of methanol concentration on the bubble temperature and hydroxyl radicals yielding. This analysis has been conducted by spanning a range of ultrasound frequency (from 140 to 515 kHz), acoustic intensity (1 and 2 W/cm(2)), and liquid temperature (from 10 to 50 degrees C). Whatever the used frequency (140-515 kHz), the variation of bubble temperature and OH formation has been negatively impacted in the presence of methyl alcohol, with a plateau from 0.1 mM methanol. On the other side, the evolution of the peak temperature and OH production were found to be frequency dependent. Moreover, in the absence of methanol, the formation of hydroxyl radicals is in the same order as that of bubble temperature (50 > 40 > 30 > 20 > 10 degrees C), whereas, in the presence of methanol, an optimal production of OH is obtained at 20 degrees C for all methanol concentrations. The decrease in bubble temperature was accelerated with the rise of liquid temperature, where no sono-activity is obtained at the liquid temperature of 50 degrees C. Based on the effects of wave frequency, acoustic intensity, and the liquid temperature, it has been concluded that the inhibition process of methanol alcohol toward the OH radicals is predominantly taking place at the bubble interface (bubble/solution region) rather than the cavitation interior (gas phase).