ABSTRACT

Ultrasonic irradiation has been investigated in the transformation of various environmentally important organic compounds. Sonochemistry results from acoustic cavitation, which is the formation and collapse of cavitation bubbles in response to ultrasonic waves. Extreme temperatures and pressures exist within the collapsing gas bubbles (Mason and Lorimer 1988), leading to thermolytic reactions and the formation of free-radical species. The conditions within the bubble are so extreme that the bubbles emit light, a phenomenon known as sonoluminescence (Young, 1976; Crum, 1994a; b; Putterman, 1995). An important reaction is the thermolysis of water vapor to form hydroxyl radical and hydrogen atoms. Thermolysis and radical reactions dominate inside the bubble and at the liquid/bubble interface. Any radicals that have not been scavenged in these regions, as well as hydrogen peroxide formed from the free-radical combination, will be available for reactions in the bulk liquid phase. Hydrolysis reactions can also be enhanced, particularly for compounds that partition to the bubble interface (Hua et al., 1995a; b; Tuulmets and Raik, 1999).