Sonochemical reduction processes in aqueous colloidal systems

The reduction of colloidal MnO2 and the formation of Au sols via the reduction of AuCl4- in aqueous solution has been found to be initiated by 20 kHz ultrasound. The presence of aliphatic alcohols was found to enhance significantly the reduction process, with the more hydrophobic alcohols showing a more marked effect at low concentrations (0.02 M). It is shown that the efficacy of the reduction reactions can be directly related to the Gibbs surface excess concentration of the alcohol at the solution-microbubble interface, irrespective of the type or bulk solution concentration of the alcohol.