KINETIC PECULIARITIES OF REDOX REACTIONS SENSITIZED BY COLLOIDAL CDS UNDER STEADY-STATE IRRADIATION - THE EFFECT OF ADSORPTION-DESORPTION PROCESSES ON THE REACTION

Photoreduction of Methyl Orange dye (MOr) by sodium sulfide was studied under steady-state photolysis (lambda = 365 nm). The reaction was sensitized by the CdS colloid with the characteristic similar to 5-nm particle size. The quantum yield of the reaction is independent of the light intensity when the latter is less than 5 mW cm(-2). The form of the dependence of the initial quantum yield of the reaction on [MOr] coincides qualitatively with the adsorption isotherm of the dye on the CdS surface. The reaction kinetics under steady-state irradiation were analyzed. The kinetics in solution as a whole are shown to be adequate to those on a single colloidal particle. On the basis of the experimental data, two types of surfaces of the colloidal particles are suggested (''open'' and ''covered'' with macromolecules of a colloid stabilizer), which significantly differ in the rate at which they establish an adsorption-desorption equilibrium with the solution.