Kinetic studies on the persulfate oxidation of methylene blue in the absence and presence of silver(I) as a catalyst in aqueous and micellar media

The kinetics and mechanism of the oxidative decolorization of methylene blue (MB+) as a cationic dye by persulfate using silver(I) catalyst in aqueous acidic medium were studied. The effects of different parameters like [H+], [Ag+], reactant concentration, micelles, and temperatures were investigated. The kinetic data showed that the oxidative decolorization of [MB](+) by persulfate obeyed pseudo-first-order kinetics by taking a large excess of [S2O82-] over [MB+]. The observed rate constant increases with increasing of [H+]. A plausible mechanism for the silver(I) enhanced decolorization of [MB](+) by persulfate is suggested which is consistent with the experimental rate law. The effect of micelles such as SDS and Triton X-100 on the reaction rate is investigated. The rate of reaction decreases with increasing [SDS] but is not affected by Triton X-100. The mechanism of the electron transfer process between [MB](+) and S2O82- proceeds through an outer-sphere mechanism. Thermodynamic activation parameters Delta H* and Delta S* were calculated. The experimental data may be useful for the layout of wastewater treatment containing various types of dyes.