Reactions of organic free radicals at colloidal silver in aqueous solution. Electron pool effect and water decomposition

Abstract

Organic free radicals of high negative redox potential such as ..cap alpha..-alcohol radicals were found to transfer electrons to colloidal silver particles stabilized by sodium dodecyl sulfate in aqueous solution. The colloidal particles thus became a pool of stored electrons that could reduce water to form hydrogen or react with suitable acceptors in solution. The organic radicals were produced by irradiation, using suitable scavengers for the primary radicals from the radiolysis of the aqueous solvent. The solutions initially contained silver ions at 1 x 10/sup -4/ - 2 x 10/sup -3/ M. At doses below 10/sup 5/ rd, the silver ions were completely reduced to form the colloidal catalyst. In this dose range, the corresponding hydrogen yield amounted to 1 molecule per 100 eV. It increased steeply at higher doses up to 3 molecules per 100 eV. The H/sub 2/ yield decreased with increasing dose rate and with increasing pH in alkaline solutions. It was highest at a concentration of sodium dodecyl sulfate of 1 x 10/sup -3/ M, i.e., far below the critical micelle concentration of this surfactant. Changes in the absorption spectrum of the colloid are attributed to changes in the size of the silver particles upon chargingmore » up with electrons. The competition of radical-colloid reactions with radical-radical deactivation in the bulk of solution or at the surface of the colloidal particles is also discussed. 11 figures.« less