Oxidants Emergence under Dual-Frequency Sonication within Single Acoustic Bubble: Effects of Frequency Combinations

The sonochemical activity of an oxygen bubble formed in an aqueous medium and oscillating under a dual-frequency excitation is studied in this paper. Several couples of frequencies are formed amongst 35, 140, 300, and 515 kHz, with a maximum acoustic amplitude of 1.5 atm. The molar yields of the emerging oxidants are analyzed in accordance with the combined frequencies and compared to the cases of mono-frequency excitations of similar maximum amplitude, i.e., 1.5 atm. Qualitatively, passing from a mono to a dual-frequency excitation demonstrated to be with no effect on the predominant species which remain 𝐻𝑂•, 𝐻𝑂2•, 𝑂 and 𝑂3. However, the results exhibited a very selective quantitative evolution depending on the combined frequencies. Some couples proved to induce a negative effect and reduce the production at the single bubble level, particularly with basic frequencies of 140 and 300 kHz, while some others demonstrated a noticeable enhancement such as the couples (35, 140 kHz) and (515, 35 kHz), as compared to mono-frequency fields.