Chemical structure-based predictive model for the oxidation of trace organic contaminants by sulfate radical

Abstract

Second-order rate constants [Formula: see text] for the reaction of sulfate radical anion (SO₄^•-) with trace organic contaminants (TrOCs) are of scientific and practical importance for assessing their environmental fate and removal efficiency in water treatment systems. Here, we developed a chemical structure-based model for predicting [Formula: see text] using 32 molecular fragment descriptors, as this type of model provides a quick estimate at low computational cost. The model was constructed using the multiple linear regression (MLR) and artificial neural network (ANN) methods. The MLR method yielded adequate fit for the training set (R_training²=0.88,n=75) and reasonable predictability for the validation set (R_validation²=0.62,n=38). In contrast, the ANN method produced a more statistical robustness but rather poor predictability (R_training²=0.99andR_validation²=0.42). The reaction mechanisms of SO₄^•- reactivity with TrOCs were elucidated. Our result shows that the coefficients of functional groups reflect their electron donating/withdrawing characters. For example, electron donating groups typically exhibit positive coefficients, indicating enhanced SO₄^•- reactivity. Electron withdrawing groups exhibit negative values, indicating reduced reactivity. With its quick and accurate features, we applied this structure-based model to 55 discrete TrOCs culled from the Contaminant Candidate List 4, and quantitatively compared their removal efficiency with SO₄^•- and OH in the presence of environmental matrices. This high-throughput model helps prioritize TrOCs that are persistent to SO₄^•- based oxidation technologies at the screening level, and provide diagnostics of SO₄^•- reaction mechanisms.

Keywords: Degradation kinetics; Group contribution method; Mechanism; Second-order rate constant; Sulfate radical.