Surface chemistry of colloidal silver: surface plasmon damping by chemisorbed iodide, hydrosulfide (SH-), and phenylthiolate

Abstract

The optical changes that occur upon the addition of iodide, iodine, and colloidal silver iodide to a colloidal solution of silver particles 6 nm mean diameter were monitored spectrophotometrically. For small concentrations of added I and I2 formation of less than a monolayer of adsorbate , the changes in the shape of the silver plasmon absorption band are practically identical. Silver iodide particles in contact with silver particles affect the plasmon band only slightly. It is concluded that the AgI molecules formed by the surface oxidation of the Ag particles by iodine do not possess the properties of bulk AgI. The structure Ag delta I is proposed as in the case of adsorbed iodide. With increasing amounts of AgI on the silver particles, the optical properties of bulk AgI appear. The coadsorption of I and SH was also investigated. SH is adsorbed more strongly than I . In fact, SH displaces I even at coverages smaller than one monolayer, which is explained by an electronic mechanism SH donating electron density into the silver particle to shift the adsorption desorption equilibrium of I . The coadsorption of SH and C6H5S was also investigated. The two anions are about equally strongly bound to the silver surface. I , SH , and C6H5S ions lose their CTTS absorption bands when they are adsorbed