| Autor: |
Qin W; Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou 510275, China., Guo K; Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou 510275, China., Chen C; Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou 510275, China., Fang J; Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou 510275, China. |
| Abstrakt: |
Hydroxyl radical (HO • ) and chlorine atom (Cl • ) are common reactive species in aqueous environments. However, the intrinsic difference in their reactions with organic compounds has not been revealed. This study compared the reaction mechanisms of HO • and Cl • with 13 aromatic and 11 aliphatic compounds by quantum chemical calculation and laser flash photolysis. Both HO • and Cl • can spontaneously react with aromatic compounds via radical adduct formation (RAF), hydrogen atom transfer (HAT), and single electron transfer (SET) pathways. The SET reactions of Cl • were more thermodynamically favorable than HO • , but contrary results were obtained for HAT reactions. According to the free energy of activation (Δ G aq ‡ ), the dominant oxidation mechanisms of aromatic compounds were RAF and SET by HO • and SET by Cl • . The important role of SET in the HO • reactions with aromatic compounds was further verified by accurately calculating the solvation free energy of HO • /HO - and experimentally tracking the radical cations, which were generally neglected in previous studies. Meanwhile, the Δ G aq ‡ value of each reaction pathway of Cl • was lower than that of HO • , resulting in higher rate constants of Cl • with aromatic compounds than HO • . For saturated aliphatic compounds, HAT was found to be the only mechanism accounting for their transformation by HO • and Cl • . This study proposed general rules for the reaction mechanisms of HO • and Cl • and unraveled their differences in the aspects of thermodynamics and kinetics, providing fundamental information for understanding contaminant transformation in processes involving HO • and Cl • . |
