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

Abstract

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 [S 2 O 8 2− ] 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 S 2 O 8 2proceeds through an outer-sphere mechanism. Thermodynamic activation parameters ΔH* and ΔS* were calculated. The experimental data may be useful for the layout of wastewater treatment containing various types of dyes.

New heterometallic Co/Zn, Ag/Co, and Ag/Zn imidazolates: structural characterization and catalytic activity in the oxidation of organic compounds

“…We were initially convinced that the presence of silver ions should be enough to secure the activity of the complex in the oxidation reaction because silver ions are used as a catalyst of oxidation in similar systems. 81 Thus we expected that 5 will demonstrate similar catalytic activity to 6 , but this was not the case. Probably the concerted action of Co and Ag is needed to accelerate the reaction.…”