PHOTOCHEMISTRY OF COLLOIDAL SILVER PARTICLES - THE EFFECTS OF N2O AND ADSORBED CN-

Colloidal silver particles (approximately 3 nm diameter) are photo-oxidized in aqueous solution in the presence of nitrous oxide, the quantum yield increasing with decreasing wavelength. Nitrogen is formed simultaneously. The effect is explained by photo-electron emission from the particles, followed by the capture of the emitted electrons by N2O. In the presence of propanol-2, the silver particles are not destroyed but catalyse the photo-decomposition of N2O. - Silver particles carrying adsorbed CN- ions are also photo-oxidized even in the absence of N2O. At the same time, hydrogen is formed by reduction of the aqueous solvent. The silver particles even dissolve when illuminated at 420 nm, i.e. into the long-wavelength tail of the plasmon absorption band. The effect is attributed to enhanced photo-electron emission due to 1) the increased negative potential of the Fermi level in the CN(-)-modified silver particles, 2) the negative overall-charge of these particles, and 3) rapid hole capture by pre-complexed surface atoms. - For a long time, metals have been thought to possess practically no photochemistry. The observations made here show that metals, when present as a fine dispersion, are demonstrably photoactive.