ABSTRACT
The sonochemical effects produced by sonolysis are due to the phenomenon of cavitation, which is the nucleation of bubbles in a liquid under the influence of ultrasound. Sonolysis is based on the fundamental concepts and theory involved in sonochemistry; the historical perspective of sonochemistry in Table 11.1 provides an insight into the discovery and understanding of fundamental processes in sonolysis. When a liquid of relatively high vapor pressure and dynamic tensile strength (such as water) is exposed to highfrequency ultrasonic waves (a few to several hundred kilohertz), acoustic cavitation in the liquid will occur. The cavitation process includes the formation, growth, and implosive collapse of small gas bubbles. Cavitation by ultrasound is accompanied by high temperature (2000 to 2500 K) and high pressure (hundreds of atmospheres), which are responsible for the degradation of organic pollutants. Therefore, sonolysis can degrade organic pollutants to CO
and H
O or convert them to compounds that are less harmful than the original compounds. The degradation of organic pollutants may result from combustion, supercritical water oxidation, and oxidation by radicals such as hydroxyl radicals and hydrogen radicals. Sonolysis was found to be efficient and economical to decontaminate industrial organics before they are discharged into aquatic ecosystems. Therefore, the applications of ultrasound to destroy organic pollutants have increased significantly in the past decade.
