Colloidal silver nanoparticles:: Photochemical preparation and interaction with O2, CCl4, and some metal ions

The optical absorption of the colloidal nanoparticles is investigated, formed by the UV illumination of aqueous solutions containing AgClO4 ((1-4) x 10(-4) M), acetone (2 x 10(-2) M), 2-propanol (1 M), and various polymer stabilizers. The 7 nm particles, which are produced in the presence of polyethyleneimine, possess an unusally narrow plasmon absorption band. The wavelength and shape of this band are affected by various adsorbed solutes; adsorption phenomena can therefore be studied spectrophotometrically. The changes in band shape that occur in the presence of oxygen and of carbon tetrachloride are attributed to a partial oxidation of the silver particles by these solutes. During the oxidation, the Fermi level in the nanoparticles shifts to a more positive potential, until the oxidation comes to a halt. Chemisorbed metal cations (Cd2+, Ni2+, Ag+, Hg2+) affect the plasmon absorption band of the silver nanoparticles more strongly the more electropositive is the metal. The effect is interpreted in terms of the donation of electron density from the silver particles to the adsorbed cations. In the case of Hg2+ ions, the electron donation leads to partial Ag oxidation and amalgam formation. UV illumination of a sol that contains Cd2+ ions produces Cd metal on the surface of the silver particles.