Study of rhodamine B degradation by persulfate

ABSTRACT Many studies have investigated the nonradical pathway of rhodamine B (RB) degradation by activated persulfate (PS). However, PS can also react with RB by direct oxidation, without activation. In this study, the kinetic and mechanistic investigation of this pathway was conducted by examining the effects of the initial PS concentration, ethanol addition, and temperature. The direct reaction between PS and RB exhibited a second-order rate constant of 0.037 M−1 s−1 at temperatures ranging from 9 to 25 °C. At elevated temperatures, the sulfate radicals (SRs) produced by the dissociation of PS react with RB and compete with direct oxidation. The reaction between SR and RB had second-order rate constants of 5.0 × 106, 1.7 × 107, 3.5 × 107, and 7.81 × 107 M−1 s−1 at 25, 40, 50, and 60 °C, respectively. A comparative study was conducted to evaluate these rate constants against those reported in the literature. A reaction scheme for the direct oxidation of RB by PS is finally proposed based on data obtained from UV-Vis and HPLC-MS2 methods.