Impact of Ultrasonic Frequency on Aqueous Sonoluminescence and Sonochemistry

Abstract

A comprehensive investigation of ultrasonic frequency and its role in sonochemical activity and sonoluminescence (SL) has been performed. SL spectra and intensity were examined at four frequencies (205, 358, 618, and 1071 kHz) and in the presence of varying argon and oxygen saturation ratios. A series of high-energy reactions induced by the extreme temperatures and pressures obtained within a microbubble during acoustic cavitation contribute to the broad continuum characteristic of SL spectra. Chemical reactivity was also measured at all four frequencies. 1,4-Dioxane decomposition and hydrogen peroxide formation were chosen as representative sonochemical processes. A 358 kHz value was the optimal frequency for maximum SL intensity and chemical reaction rates. The impact of a hydroxyl radical scavenger, bicarbonate ion, on SL intensity and H2O2 formation was also examined. Results from this investigation indicate that nonlinear bubble implosions play a more significant role at lower frequencies whereas higher species flux rates influence chemical reactivity at higher frequencies.

Single-bubble sonoluminescence

“…This form of emission due to external photoexcitation changes in the same fashion as the sonoluminescence signal, with changes in solution contents and solution concentration, and thus provides a true, amplified representation of the sonoluminescence intensity. Being closely associated with chemical reactions due to cavitation, sonoluminescence light can also serve as an indicator for sonochemistry (see below) when light intensities and chemical reaction yields are correlated (Beckett and Hua, 2001). …”

“…Nevertheless, the reaction efficiency will have to be enhanced before a more widespread use of sonochemistry is feasible. One approach to achieving higher yields is the search for an optimal frequency of the driving ultrasound (Beckett and Hua, 2001).…”

Free radical generation induced by ultrasound in red wine and model wine: An EPR spin-trapping study

“…3, the application of higher ultrasound frequencies led to an increase in the intensity of DMPO / 1-hydroxylethyl free radical spin adducts, which may be attributed to the amounts increasing of the collapsing bubbles of ultrasound caviation as reported by other authors [19][20][21]. Generally, the effect of ultrasound cavitation could be reduced at higher ultrasonic frequency, since either the rarefaction cycle of the sound wave produces a great negative pressure which is insufficient in its duration and/or intensity to initiate cavitation, or the compression cycle occurs faster than the time for the microbubble to collapse [22][23][24]. As a consequence, the collapse of bubbles occurs much more rapidly, resulting in the amounts of cavitation bubbles increased and more hydroxyl free radicals released from the bubbles, finally inducing the increase of 1-hydroxylethyl free radical and its spin adducts in model wine.…”

Stable Carbon Isotope Fractionation during Sonolysis of Di-n-butyl Phthalate

“…monoester) increased with the increasing of sonication time. Owing to some of these intermediates can further break down during sonolysis, a competitive degradation existed between DBP molecules and intermediates molecules at the late stages of degradation [7], leading to a decrease in OH concentration [8]. As a result, the amounts of OH radicals reacted with target pollutant molecules decreased, leading to the lower degradation rate of DBP.…”