Determination of the surface area of silver sols based on the rate of the electrocatalytic oxidation of N,N-dimethyl-p-phenylenediamine with chloropentaamine-cobalt(III) chloride

The rate of the electrocatalytic reaction between N,N-dimethyl-p-phenylenediamine and the cobalt(III) complex [CoIII(NH3)5Cl]2+ is proportional to the surface area of silver which acts as catalyst. For a monodisperse colloid the surface area can be calculated from the size of the particles. Thus, a calibration line can be obtained by carrying out several measurements with the same silver sol but in different concentration. Silver sols of both large particles (4.6 μm diameter) and small particles (22.6 nm) were used. These sols were prepared by reduction of silver nitrate with ascorbic acid and borohydride respectively. The calibration line allows the determination of the blank surface area of silver sols from the catalytic acceleration of the chosen standard redox reaction.