TIME-RESOLVED CHEMISORPTION OF I- AND SH- ON COLLOIDAL SILVER PARTICLES (A STOPPED-FLOW STUDY)

An aqueous silver sol (mean particle size: 6 nm) is mixed with KI and NaSH solution, and the changes in optical absorption and light scattering are recorded. When iodide adsorbs on the silver particles, the 225-nm band of I- disappears concurrently with the decreasing of the silver plasmon absorption band. In the same time range, the intensity of Light scattering slightly decreases, which is explained as a detachment of the colloidal particles from the polyphosphate stabilizer. At a later stage, the silver plasmon band is red-shifted and the light scattering finally increases again, which is understood in terms of loose cluster formation of the particles. The adsorption of H2S leads to damping and a simultaneous blue shift of the plasmon absorption band. The adsorption of H2S is faster than that of SH-, as there is no Coulomb repulsion between the adsorbant and the negatively charged metal particles.