Acoustic cavitation is responsible for both sonochemistry and sonoluminescence. Bubble collapse in liquids results in an enormous concentration of energy from the conversion of the kinetic energy of liquid motion into heating of the contents of the bubble. The high local temperatures and pressures, combined with extraordinarily rapid cooling, provide a unique means for driving chemical reactions under extreme conditions. A diverse set of applications of ultrasound to enhance chemical reactivity has been explored, with important applications in mixed–phase synthesis, materials chemistry, and biomedical uses. For example, the sonochemical decomposition of volatile organometallic precursors in low–volatility solvents produces nanostructured materials in various forms with high catalytic activities. Nanostructured metals, alloys, carbides and sulphides, nanometre colloids, and nanostructured supported catalysts can all be prepared by this general route. Another important application of sonochemistry to materials chemistry has been the preparation of biomaterials, most notably protein microspheres. Such microspheres have a wide range of biomedical applications, including their use as echo contrast agents for sonography, magnetic resonance imaging contrast enhancement, and oxygen or drug delivery.

Acoustic cavitation and its chemical consequences

The optimization of ultrasonic irradiation as an advanced oxidation technology can be achieved by adjusting the ultrasonic frequency and saturating gas during sonolysis. The sonolytic production of hydrogen peroxide (H2O2) and hydroxyl radical (•OH) has been investigated at the ultrasonic frequencies of 20, 40, 80, and 500 kHz, respectively, in the presence of four different saturating gases (i.e., Kr, Ar, He, O2) at each frequency. H2O2 was measured with a KI dosimeter, and the formation of •OH was monitored by trapping with terephthalic acid. Both the applied frequency and the physicochemical properties of the saturating gases influ ence the sonochemical rates of production of •OH and H2O2. At 20 kHz, the rate contants for the production of H2O2 vary over an order of magnitude as a function of the nature of the dissolved gas (0.0508 and 1.31 μM min-1). Similar trends are observed for the production of •OH at the same frequencies and under an identical set of saturating gases. The highest rates of produc...

Optimization of Ultrasonic Irradiation as an Advanced Oxidation Technology

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 hig...

Impact of Ultrasonic Frequency on Aqueous Sonoluminescence and Sonochemistry

OH-radical formation by ultrasound in aqueous solution--Part II: Terephthalate and Fricke dosimetry and the influence of various conditions on the sonolytic yield.

V. I. Kvochka

Papers

The effect of bulk solution temperature on the intensity and spectra of water sonoluminescence

Sonoluminescence spectra of water