Bimetallic colloids: Silver and mercury

Mercury ions, Hg2+, are radiolytically reduced in an aqueous silver sol. The plasmon absorption band of silver is blue-shifted, which is explained by the formation of a solid mercury layer around the silver particles. The metal deposition stops when the silver particles carry about two monolayers of mercury and the additionally reduced mercury forms colloidal Hg particles. Chemisorbed SH- and I- ions damp the plasmon absorption band of silver and silver-mercury particles, the effect being less pronounced with increasing mercury content of the particles. It is concluded that the collective excitation of the electron gas in the silver particles still strongly contributes to the optical absorption, even when they carry a mercury shell. The chemisorption equilibrium is shifted to the desorption side upon the deposition of excess electrons on the silver-mercury particles.