Affiliation:
1. Laboratory of Environmental Process Engineering, Faculty of Process Engineering, University Constantine 3 Salah Boubnider, P.O. Box 72, Constantine 25000, Algeria
2. Chemical Engineering Department, College of Engineering, King Saud University, P.O. Box 800, Riyadh 11421, Saudi Arabia
Abstract
Reactive oxygen species (ROS) and reactive chlorine species (RCS) and their involvement in the degradation process are explored in this work by thorough kinetic modeling of the solar-activated hypochlorite degradation of Rhodamine B (RhB) dye. The kinetic modeling enabled the determination of rate constants for both radical and non-radical pathways of hypochlorite and the oxidation of RhB by free radicals. Using COPASI® software, fed with a kinetics mechanism of 144 chemical reactions, the free radical kinetic model accurately fitted experimental data under various conditions, including temperatures ranging from 25 to 55 °C and initial hypochlorite concentrations from 300 to 1000 µM, at a controlled pH of 11. Results indicate that increasing hypochlorite dosages and temperatures enhance free radical concentrations and RhB degradation rates. •OH and ClO• radicals were quantified as primary contributors to RhB degradation, while ozone played a minor role. The model provides profiles for ROS and RCS, details on radicals distribution in RhB degradation, and predictions of rate constants for the photolysis of ClO−: kR1 = 2.67 × 10−4 s−1 for the radical pathway (ClO− →hν O•− + Cl•), and kR2 = 1.88 × 10−5 s−1 and kR3 = 0 s−1 for the non-radical pathway (i.e., ClO− →hν O(3P) + Cl− and ClO− →hν O(1D) + Cl−, respectively). The rate constants for RhB reactions with O•−, Cl•, Cl2•− and ClO• were predicted to be 4.8 × 109 M−1 s−1, 1.45 × 109 M−1 s−1, 2.5 × 107 M−1 s−1 and 8.7 × 104 M−1 s−1, respectively. Lower rate constants were predicted for RhB reactions with HOCl•−, HO2•, O2•−, and O(3P), with values of 4.1 × 104 M−1 s−1, 7.3 × 105 M−1 s−1, 3.6 × 104 M−1 s−1, and 0.40 M−1 s−1, respectively.