Abstract
Metal colloids have been widely studied in recent years, because their physical and chemical properties are often quite different from those of the bulk materials. Various methods to prepare nanoparticles from metal ions in an aqueous solution have been proposed, and a sonochemical preparation is one of the unique methods, as the organic additives such as alcohols and surfactants can be used as the reducing agents. The formation rates of gold, silver and platinum nanoparticles were studied by using an ultrasonic cleaning bath of 20, 200 or 600 kHz frequencies, and it was found that the formation rate was controllable by selecting the type of the additives as well as the hydrogen ion concentration in the solution. When lower alcohols such as methanol or ethanol were used, the formation rate of gold or platinum nanoparticles in the neutral region of pH was rapid comparing with that in acid region or alkaline region. The formation rate of gold or platinum nanoparticles using higher alcohol such as pentanol or hexanol was higher than that using lower alcohol at low pH conditions. However, the formation rate became very slow at higher pH than 9.5, when butanol, pentanol or hexanol was used as an additive. On the other hand, for the preparation of silver nanoparticles, the formation rate at higher pH than 9 adjusted by ammonium was extremely high due to the silver-ammonium ion complex.
