Mechanistic insights into carbonate radical-driven reactions: Selectivity and the hydrogen atom abstraction route

Yu Li; Jun Teng; Jia Wu; Sai Zhang; Zhiwei Zhao; Li Li

doi:10.1016/j.jhazmat.2024.136930

Mechanistic insights into carbonate radical-driven reactions: Selectivity and the hydrogen atom abstraction route

J Hazard Mater. 2024 Dec 21:485:136930. doi: 10.1016/j.jhazmat.2024.136930. Online ahead of print.

Authors

Yu Li¹, Jun Teng¹, Jia Wu¹, Sai Zhang¹, Zhiwei Zhao², Li Li¹

Affiliations

¹ Key Laboratory of Eco-Environments in Three Gorges Reservoir Region, Ministry of Education, College of Environment and Ecology, Chongqing University, Chongqing 400045, PR China.
² Key Laboratory of Eco-Environments in Three Gorges Reservoir Region, Ministry of Education, College of Environment and Ecology, Chongqing University, Chongqing 400045, PR China; School of Civil and Transportation Engineering, Guangdong University of Technology, Guangzhou 510006, PR China. Electronic address: hit_zzw@163.com.

PMID: 39709807
DOI: 10.1016/j.jhazmat.2024.136930

Abstract

Carbonate radical (CO₃^•) is inevitably produced in advanced oxidation processes (AOPs) when addressing real-world aqueous environments, yet it often goes unnoticed due to its relatively lower reactivity. In this study, we emphasized the pivotal role of CO₃^• in targeting the elimination of contaminants by contrasting it with conventional reactive oxygen species (ROSs) and assessing the removal of sulfamethazine (SMT). Similar to singlet oxygen (¹O₂), CO₃^• shows a preference for electron-rich organic compounds. In addition, hydrogen atom abstraction (HAA) was determined as the primary pathway in CO₃^•-driven reactions, with a lower free energy barrier (∆G^‡) compared to the addition process, while single electron transfer (SET) was found to be thermodynamically unfavorable in all selected aromatics with varying substituents, using DFT calculations. The H atoms within amino groups (NH₂ and NH) were shown to be the most susceptible to abstraction by CO₃^•, which is more facile than hydroxyl radical (^•OH) due to the shorter NH bond cleavage length. Finally, the degradation intermediates of SMT by CO₃^• were identified, with SO₂ extraction, the cleavage of SN and CN bonds, and nitration/nitrosation of NH₂ groups being the main degradation pathways. The results from this study are expected to set the stage for the large-scale utilization of CO₃^• and advance our understanding of its reaction characteristics.

Keywords: Carbonate radical; DFT calculations; H atom abstraction; Reaction mechanism; Selectivity.