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Quantitative structure-activity relationship models for predicting reaction rate constants of organic contaminants with hydrated electrons and their mechanistic pathways

Li, Chao, Zheng, Shanshan, Li, Tiantian, Chen, Jingwen, Zhou, Junhui, Su, Limin, Zhang, Ya-Nan, Crittenden, John C., Zhu, Suiyi, Zhao, Yuanhui
Water research 2019 v.151 pp. 468-477
Gibbs free energy, dehalogenation, electron transfer, electrons, energy, models, organic compounds, pollutants, pollution control, prediction, quantitative structure-activity relationships, quantum mechanics, wastewater treatment
The hydrated electron (eaq−)-based reduction processes are promising for removing organic pollutants in water engineering systems. The reductive kinetics, especially the second order rate constants (keaq−) of eaq− with organic compounds, is important for evaluating and modeling the advanced reduction processes. In this study, the keaq−values for aliphatic compounds and phenyl-based compounds are, for the first time, modeled by the quantitative structure-activity relationship (QSAR) method. The structural features governing the reactivity of two classes of organic compounds toward eaq− were revealed, and the energy of the lowest unoccupied molecular orbital (ELUMO), one-electron reduction potential (ERED) and polarizability (α) were found to be the important molecular parameters in both two models. The built QSAR models provide robust predictive tools for estimating the removal of emerging pollutants using eaq− during wastewater treatment processes. Additionally, quantum chemical calculations were employed to probe into the mechanism and feasibility of the single electron transfer (SET) pathway in the eaq−-based reduction process. The thermodynamic investigation suggests that the compounds with electron-withdrawing groups tend to possess higher keaq− and lower Gibbs free energy (ΔGSET) and Gibbs free energies of activation (∆‡GSET∘) than the ones with electron-donating groups, indicating the SET process occurs more readily. It is also found that the refractory halogenated compounds can achieve dehalogenation via the SET pathway.