Abstract
The redox decolorization of direct violet 31 [DV-31](-) by Ag(I)/S2O8 (2-) under conditions similar to the Fenton process was studied kinetically in aqueous solution over a range of different concentrations of dye and redox system. The oxidation rate increases with decreasing pH. The reaction is catalyzed by Ag(I) through the formation of Ag(II) which is a very strong oxidizing agent. A tentative mechanism for silver(I) catalyzed oxidation of [DV-31](-) by peroxydisulfate is proposed. Pseudo-order conditions were maintained in all experiments by using an excess of S2O8 (2-) (> 10-fold). The reaction obeys the following rate law:The magnitudes of the thermodynamic activation parameters suggest that electron transfer proceeds through an outer-sphere mechanism. Sodium dodecylsulfate (SDS) was found to decrease the rate of reaction due to attraction of the Ag(I) ion into the SDS pseudo-phase, leaving other reactants in the bulk solution. Additionally, H-1 NMR spectra of [DV-31](-) before and after degradation confirmed almost complete mineralization of the dye.