SURFACE-CHEMISTRY OF COLLOIDAL SILVER IN AQUEOUS-SOLUTION - OBSERVATIONS ON CHEMISORPTION AND REACTIVITY

Colloidal silver particles (3-nm diameter) are oxidized in the absence of air by organic and inorganic electron acceptors (such as nitrobenzene, methylviologen, nitropyridine oxide, and hexacyanoferrateIII) when nucleophilic reagents (such as CN- and SH-) are present in the solution. The mechanism of catalyzed metal oxidation proposed previously 2, according to which the interaction of surface atoms with the nucleophiles leads to an excess negative charge in the metal interior which can be picked up by the electron acceptors, explains the observed phenomena. This mechanism contains reversible steps. An experiment is reported in which the reverse sequence of events is observed: chemisorption of Ag(CN)2- on silver particles, producing an excess positive charge inside the particles, followed by complete reduction of the Ag+ ions of the adsorbed complexes by excess electrons that are deposited by a reducing reagent (i.e., organic radicals generated radiolytically). Ag(CN)2- ions in solution are not reduced by radicals.