SONOCHEMICAL FORMATION OF GOLD PARTICLES IN AQUEOUS-SOLUTION

Gold(III) ions in aqueous solutions of NaAuCl4 were reduced to form go ld particles by ultrasonic irradiation, The rate of formation of gold particles was accelerated in the presence of certain organic additives such as surfactants, water-soluble polymers and aliphatic alcohols an d ketones. The rates of formation of gold particles from 1 mM Au(III) ions in pure water were 3 mu M min(-1) under argon atmosphere and appr oximately zero under air, and in solutions containing additive the rat es were 9-133 mu M min(-1) under argon and 8-40 mu M min(-1) under air , Surfactants stabilized the particles as colloidal state for more tha n several months, The rates of formation of both hydrogen atoms and hy droxyl radicals were estimated to be equal to 25 mu M min(-1) in the s onolysis of pure water under argon. Three reaction pathways leading to the reduction of metal ions were proposed: (1) reduction by hydrogen atoms; (2) reduction by reducing radicals formed via reactions of hydr oxyl radicals or hydrogen atoms with the additives; (3) reduction by r adicals formed from thermal reaction of the additives at the interfaci al region between cavitation bubbles and bulk solution and/or in the c avities. The order of the contribution of these three pathways to the reduction of gold ions was (3) > (2) > (1) in most cases, The number a verages of the size of gold particles formed in surfactant solutions u nder argon atmosphere were about 10 nm with a fairly narrow size distr ibution. (C) 1996 by Radiation Research Society