Quantitative structure–activity relationships for the reaction kinetics of trace organic contaminants with one-electron oxidants†

Abstract

Understanding the reactivity between trace organic contaminants (TrOCs) and radicals involved in advanced oxidation processes (AOPs) is necessary for a good process design, but the experimentally determined rate constants (k values) are not sufficient for numerous artificial TrOCs. Thus, the development of quantitative structure–activity relationships (QSARs) for predicting k values may be an effective way to address this limitation. In this work, we developed QSARs for the reactions of TrOCs with AOP-related one-electron oxidants. Specifically, 15 QSARs using Hammett constants and 8 cross-correlations were developed based on the k values of over 400 reactions between TrOCs (most contain electron-rich moieties, such as phenol, aniline, and alkoxy benzene) and 5 one-electron oxidants (SO₄˙⁻, Br˙, Br₂˙⁻, Cl₂˙⁻, and CO₃˙⁻). Overall, the developed QSARs show a good predictive performance with 94% (237/251, for Hammett constant-based QSARs) and 80% (218/274, for cross-correlations) of the k values predicted within a factor of 3. All the Hammett constant-based QSARs show negative slope values and all cross-correlations show positive relationships, suggesting all 5 one-electron oxidants mainly share similar electrophilic mechanisms with the TrOCs highlighted in this work. Previous QSAR studies on the k values of one-electron oxidants were compared and integrated into their model analysis. Furthermore, k values predicted herein from the QSARs were used to evaluate the degradation of TrOCs during UV/persulfate and UV/chlorine treatment in multiple wastewater matrices, which were demonstrated to be useful. Finally, remarks on the use of the developed QSARs were presented.