Radiation-chemical reduction of Co2+ ions in aqueous solution. Metal sols and their properties

The radiation-chemical reduction of Co2+ ions in an aqueous solution of Co( ClO4)(2) containing sodium formate was studied. Stable metal sols containin g spherical particles with a diameter of 2-4 nm are formed under gamma-irra diation in the presence of polyacrylate as the stabilizing additive. An aqu eous solution of colloidal cobalt has an optical absorption that increases smoothly in the UV region without a maximum to 200 nm (epsilon(200) = 1.3.1 0(4) mol(-1) L cm(-1)). It is established that the radiation-chemical reduc tion of the Co2+ ions occurs via an autocatalytic mechanism. The metal sols catalyze the reduction of the Co2+ ions by CO2.- radical ions formed under irradiation. The properties of the sols were studied, and it is shown that they are readily oxidized by hydrogen peroxide and other oxidants. The mec hanism of chemical reactions involving the sols is discussed.