SPONTANEOUS FORMATION OF SILVER PARTICLES IN BASIC 2-PROPANOL

Silver ions are spontaneously reduced in basic, air-saturated solution s of 2-propanol to yield stable Ag colloids in the presence of powdere d Naflon. The metal particles (7.4 nm mean diameter) react with oxygen to form Ag2O upon exposure to UV light. Changes in the absorption ban d of the Ag colloid are observed when the metal particles are in conta ct with Ag2O particles. The optical changes are explained in terms of surface effects of the metal particles that arise from metal-metal oxi de interactions. Kinetic results indicate that the reduction of Ag+ io ns is an autocatalytic process. Small metal particles deposited on the surface of larger oxide particles act as catalyst for reduction proce ss. The kinetic observations are consistent with a simple autocatalyti c model which correlates autoacceleration with increases in the number of Ag particles. It is proposed that reduction of Ag+ ions takes plac e on the Ag2O surface whereas oxidation of the solvent molecules occur s on the surface of metal particles.