Acoustic cavitation for engineering of gold sols in silver nitrate solutions

Binary gold–silver nanostructures of preformed gold nanoparticles (25 nm) in silver nitrate solutions are produced by a two step sonication (20 kHz). Ultrasonic treatment of gold–silver mixtures is carried out in the presence of sodium dodecyl sulfate in water or 2-propanol, and poly(vinyl pyrrolidone) in ethylene glycol solutions. Gold–silver nano-worms, which consist of ripened gold particles connected by ultrasonically reduced silver, are formed after 1 h of sonication in the presence of sodium dodecyl sulfate aqueous solution. In 2-propanol bimetallic nano-worms have a well defined core–shell structure. Polygonal alloy nanoparticles with gold as a core material and a silver shell are produced after 180 min of sonication in the presence of poly(vinyl pyrrolidone) in ethylene glycol solution. Bimetallic gold–silver nanostructures have defected face centered cubic structure and represent polycrystals with a large number of crystallites randomly oriented. For the first time, the mechanism of gold particle design by ultrasound is examined in detail. The role of additives (sodium dodecyl sulfate, polyvinyl pyrrolidone, ethylene glycol and 2-propanol) as reductants of silver at the gold contact surface or stabilizers of particles is highlighted.