Sonochemistry and sonoluminescence in aqueous AuCl4- solutions in the presence of surface-active solutes

The 515 kHz ultrasound-initiated reduction of AuCl4- to Au(0) was examined as a function of the concentration of various surface-active solutes. The a mount of AuCl4- reduced in the presence of ethanol, propan-1-ol, and butan- 1-ol was found to be dependent on the surface excess of the alcohol at the gas/solution interface, i.e., the relative concentration of the alcohol at the gas/solution interface compared to the bulk solution concentration. The efficiency of reduction of AuCl4- in the presence of the surfactants sodiu m dodecyl sulfate or octaethylene glycol monodecyl ether was found to be re lated to the monomer concentration of the surfactant in solution. The light emitted (sonoluminescence) during ultrasonic irradiation of the aqueous so lutions was also monitored and compared with the trends observed in the son ochemical experiments. The sonoluminescence was observed to be significantl y reduced in the presence of alcohol, and the effect was correlated with th e surface excess of the alcohols at the gas/solution interface. In contrast , the effect of the surfactants on the sonoluminescence was highly dependen t on concentration and headgroup type of the surfactant.