Sonochemistry

Abstract

Sonochemistry is a relatively new term that arrived on the scene in the late 1970s and was then simply defined as the uses of ultrasound in chemistry and processing. Ultrasound is part of the overall sound spectrum, but is generally classified as sound beyond the frequency that can be detected by the human ear. Sometimes called “silent sound” it ranges from 20 kHz to 10 MHz within which it can be roughly subdivided into three main regions: low frequency, high power ultrasound (20–100 kHz); intermediate frequency, medium power ultrasound (100 kHz–1 MHz); and high frequency, low power ultrasound (1–10 MHz). The range from 20 kHz to 1 MHz is generally used in sonochemistry, whereas frequencies > 1 MHz are more commonly used in nondestructive testing and medicine. The driving force for sonochemistry is acoustic cavitation, which is the formation of small cavities in a fluid produced by ultrasound that undergo highly energetic collapse. A number of text books have been published that explore different aspects of sonochemistry. This article aims to provide the readers with a fundamental understanding of acoustic cavitation and its associated physical and chemical effects. Detailed information on the events that are involved in acoustic cavitation is discussed in the first section. Among the major effects generated by acoustic cavitation is Sonoluminescence and Sonochemistry, but only brief information is provided on the former since it is not the primary focus of this article. The majority of the discussion is focused upon Sonochemistry within which reactions have been subdivided into different categories, as suggested in the literature. Although sonochemistry is useful for a variety of applications, two areas that are particularly prominent are materials synthesis and the degradation of organic pollutants.

Selected Applications of Ultrasonics in Food Processing

“…13 The effect of Tween 40 concentration on particle size D [3,2] of flaxseed oil in water emulsion prepared by microfluidisation (Reproduced with permission from [38]) by forcing it through a 10 mm orifice atomizer. The winemist was collected after 4, 8, 12 and 16 passes and compared to conventionally aged rice and maize wines, respectively.…”

“…It is for this reason that sonication of air-saturated solutions can lead to a decrease in the pH. Further details of the phenomenon of acoustic cavitation have been described elsewhere [2] and the reader is directed to this review article.…”

Effect of sonication frequency on the disruption of algae

“…Bioeffects caused by acoustic streaming have been confirmed to occur in cell cytoplasm [19]. The second type comprises cavitation effects, which consist of both chemical and physical effects, for example, free radical reactions, shock waves, shear stress, and microjet [20]. Although chemical effects have been reported as a major cause of inactivation [21], inactivation mechanisms due to shock waves [22] and shear stress of microstreaming [23] have also been suggested.…”

A convenient synthesis of pyrandione derivatives using P-toluenesulfonic acid as catalyst under ultrasound irradiation

“…Ultrasounds can promote for realizing many reactions [11][12][13], most of the effects arise from cavitations [14][15]. In the literature, it is shown that increase in yield is observed upon condensation reaction using ultrasounds.…”