Combined kinetic and spectroscopic study of oxidation of azo dyes in surfactant solutions by hypochlorite

Abstract

Combined kinetic, spectroscopic and thermodynamic investigations have been carried out to examine the influence of cationic, anionic and nonionic surfactants upon the oxidation of an azo dye, II, by hypochlorite. Oxidation rates were unaffected by the presence of anionic or nonionic surfactant (SDS or C 12E 5) either in micellar or submicellar regions: indicating the absence of any specific dye–surfactant interactions. On the other hand, specific interactions were observed with cationic surfactants, both in submicellar and micellar regions. Addition of CTAts to dye II produced a reduction in intensity of its UV–vis spectrum and caused oxidation rates to decrease. These are attributed to formation of a sparingly soluble 1:1 complex with the dye, via interactions with the sulfonate groups. Binding of DTAC to the dye in sub-micellar regions results in a slight enhancement in oxidation rates, which is attributed to break-up of small, soluble dye aggregates. In micellar regions, there was evidence that the dye becomes incorporated into the surface of micelles formed by both cationic surfactants, where they become inert to reaction with hypochlorite.