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 ( = 365 nm). The reaction was sensitized by the CdS colloid with the characteristic 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.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 244–254, February, 1995.This work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-4816).