Free radical formation and scavenging by solutes in the sonolysis of aqueous solutions

Abstract

It has long been known that the primary radicals generated in water (H and OH), on the collapse of acoustic bubbles, largely recombine. It has been estimated that as much as 90% react within the bubble to produce molecular hydrogen, hydrogen peroxide and water [Henglein, Ultrason. Sonochem.2, S115–S121 (1995)]. This high recombination efficiency has been likened to radicals reacting within “spurs” produced by ionizing radiation in water. Several studies have shown that by using high concentrations (100s of mM) of primary radical scavengers, e.g., aliphatic alcohols, iodide, etc., a large number of the primary radicals are able to be captured in acoustically produced hot spot spurs. What is less well examined is the effect the scavengers themselves have on the production of the primary radicals and hence on the radical yields measured. The talk will consider the effect that typical radical scavengers have on active bubble populations in aqueous solutions, and on the production of primary radicals in the presence of added solutes.