Effect of water matrix on sulfate radical behavior during BTB degradation by activated persulfate

One of the primary constraints on the use of activated persulfate (PS), a precursor of the sulfate radical (SR), is a lack of understanding of its reaction pathways in the subsurface. SRs can degrade the target dye Bromothymol Blue (BTB) depending on several parameters, including the initial concentrations of PS and BTB, time, water salts cations (Na+ and K+), ionic strength, catalytic ions (), and temperature. Experiments and numerical simulations using the established kinetic model yielded second-order rate constants for the reaction of BTB with the dominant SR at pH 3 of (1.1 ± 0.55) × 108, ((1.5 ± 0.77) × 108, (1.9 ± 0.95) × 108 and (2.2 ± 1.1) × 108 M-1 s-1 at 40, 50, 60, and 70°C, respectively. These rate constants were used to calculate the kinetic activation parameters (Ea, ∆H≠, ∆S≠, ∆G≠) according to the Arrhenius and Eyring equations. The results obtained are as follows: 19.8 kJ mol-1, 16.36 kJ mol-1, - 0.038 kJ mol-1 K-1, and 27.78 kJ mol-1. Finally, a possible mechanism for the discoloration of BTB by SR is proposed, in which the destruction of aromatic ring structures occurs alongside the discoloration of BTB.