Scavenging of OH radicals produced in the sonolysis of water

The yield of hydrogen peroxide in the ultrasonic irradiation of argon saturated water was studied in the presence of various solutes. The efficiency of OH radical scavenging is expressed by 1/c/sub 1/2/, i.e. the reciprocal solute concentration at which the H/sub 2/O/sub 2/ yield is decreased by 50%. c/sub 1/2/ ranges over several orders of magnitude. It is not related to the specific reactivity towards OH in homogeneous solution. However, it is correlated to the hydrophobicity R of the solutes (R = ratio of hydrophobic groups, such as CH/sub 3/ and CH/sub 2/, to hydrophylic groups, such as OH, NH/sub 2/ or COOH, in a solute molecule). The competition between I/sup -/ and a second solute for OH also was studied. The competition between I/sup -/ and HCO/sub 2//sup -/ follows similar kinetics as in homogeneous solution. However, many other solutes compete in the manner which would be expected if radical scavenging occurred in different phases. The effects are explained in terms of OH radical formation in oscillating argon bubbles, combination of OH radicals to form H/sub 2/O/sub 2/ in an interfacial area, and enrichment of hydrophobic solutes in the bubbles