Identifying the Persistent Free Radicals (PFRs) Formed as Crucial Metastable Intermediates during Peroxymonosulfate (PMS) Activation by N-Doped Carbonaceous Materials
- Yufei ZhenYufei ZhenState Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, Harbin 150090, P. R. ChinaMore by Yufei Zhen,
- Shishu ZhuShishu ZhuSchool of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, P. R. ChinaGuangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou 510275, P. R. ChinaMore by Shishu Zhu,
- Zhiqiang Sun* ,
- Yu TianYu TianState Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, Harbin 150090, P. R. ChinaMore by Yu Tian,
- Zeng LiZeng LiState Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, Harbin 150090, P. R. ChinaMore by Zeng Li,
- Chen Yang , and
- Jun Ma*
A nonradical mechanism involved in peroxymonosulfate (PMS) activation in carbonaceous materials (CMs) is still controversial. In this study, we prepared N-doped CMs, including hollow carbon spheres (NHCSs) and carbon nanotubes (N-CNTs), to probe the crucial intermediates during PMS activation. The results suggested that the higher efficiency and lower activation energy (13.72 kJ mol–1) toward phenol (PN) degradation in an NHCS/PMS system than PMS alone (∼24.07 kJ mol–1) depended on a typical nonradical reaction. Persistent free radicals (PFRs) with a g factor of 2.0033–2.0045, formed as crucial metastable intermediates on NHCS or N-CNT in the presence of PMS, contribute largely to the organic degradation (∼73.4%). Solid evidence suggested that the formation of PFRs relied on the attack of surface-bonded •OH and SO4•– or peroxides in PMS, among which surface-bonded SO4•– was most thermodynamically favorable based on theoretical calculations. Electron holes within PFRs on NHCSs shifted the Fermi level to the positive energy with the valance band increasing from 1.18 to 1.98 eV, promoting the reactivity toward nucleophilic substances. The degradation intermediates of aromatic compounds (e.g., PN) and electron rearrangement triggered the evolution of PFRs from oxygen-centered to carbon-centered radicals. Moreover, due to the specific electron configuration, graphitic N on NHCS was critical for stabilizing the PFRs. This study provides insightful understanding of the fate of organic contaminants and the structure–activity relationship of reactivity of CMs toward PMS activation.
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