Optical and Chemical Observations on Gold−Mercury Nanoparticles in Aqueous Solution

The γ-radiolytic reduction of Hg 2+ in aqueous solution in the presence of 0.3 M 2-propanol first leads to Hg 2 2+ (ε 237 nm = 3.2 × 10 4 M -1 cm -1 ), and later to colloidal mercury. When the reduction is carried out in the presence of colloidal gold nanoparticles, Hg 2 2+ does not appear as an intermediate, and Hg 2 2+ formed in the absence of gold does not react with added gold colloid. These effects are understood in terms of the reaction of a precursor, Hg +, with the gold particles. The optical absorption spectra of the resulting mercury containing gold particles are reported for various Au/Hg ratios. The plasmon absorption band of gold is blue-shifted and damped, and a broad absorption band develops around 360 nm with increasing mercury content. The mercury of the composite particles is slowly reoxidized upon exposure of the solution to air. Excess Hg 2+ ions in solution extract adsorbed mercury in the form of Hg 2 2+ . Both the absorption spectra and electron micrographs of the gold particles are interpreted by a rather weak penetration of mercury into the particles and formation of a rather labile mercury layer around them.