Key Laboratory of Building Safety and Energy Efficiency, Ministry of Education, Department of Water Engineering and Science, College of Civil Engineering, Hunan University, Changsha, 410082, China.
Key Laboratory of Building Safety and Energy Efficiency, Ministry of Education, Department of Water Engineering and Science, College of Civil Engineering, Hunan University, Changsha, 410082, China.
Water Res. 2021 Apr 15;194:116938. doi: 10.1016/j.watres.2021.116938. Epub 2021 Feb 16.
The UV/monochloramine (NHCl) process is an advanced oxidation process that can effectively remove emerging contaminants (ECs). However, the degradation mechanisms of reactive radicals with ECs are not clear. In this work, we combined theoretical calculations with experimental studies to investigate the kinetics and mechanism of radical-mediated degradation of paracetamol (AAP) in UV/NHCl process. The degradation of AAP in UV/NHCl process accords with the pseudo first-order kinetics. Impact factors including NHCl dose, pH, natural organic matter, HCO, and NO were evaluated. The reaction mechanisms of AAP with hydroxyl radical (HO), reactive chlorine species (RCS), and reactive nitrogen species (RNS) were discussed in detail. Specifically, HO attacked AAP mainly through hydrogen atom transfer (HAT) and radical adduct formation (RAF), while Cl play a certain role through single electron transfer (SET). NH and Cl destructed AAP mainly through HAT. Based on the mechanism analysis, the second-order rate constants of AAP reacts with HO, Cl, NH, ClO, Cl and NO were calculated through transition state theory as 2.66×10 M s, 2.61×10 M s, 1.02×10 M s, 7.74×10 M s, 1.32×10 M s, 1.48×10 M s respectively. The second-order rate constants were then used to distinguish the contribution of radicals to the degradation of AAP. Thirteen transformation products were identified by high-resolution mass spectrometry. Combined active sites with potential energy surface, the detailed reaction pathways were proposed. Overall, this study provides deep insights into the mechanism of radical-mediated degradation of AAP.
UV/一氯胺（NHCl）工艺是一种高级氧化工艺，可有效去除新兴污染物（ECs）。然而，活性自由基与 ECs 的降解机制尚不清楚。在这项工作中，我们结合理论计算和实验研究，研究了 UV/NHCl 工艺中活性自由基介导的扑热息痛（AAP）降解动力学和机制。UV/NHCl 工艺中 AAP 的降解符合准一级动力学。评估了包括 NHCl 剂量、pH 值、天然有机物、HCO 和 NO 在内的影响因素。详细讨论了 AAP 与羟基自由基（HO）、活性氯物种（RCS）和活性氮物种（RNS）的反应机制。具体而言，HO 主要通过氢原子转移（HAT）和自由基加合物形成（RAF）攻击 AAP，而 Cl 通过单电子转移（SET）发挥一定作用。NH 和 Cl 主要通过 HAT 破坏 AAP。基于机制分析，通过过渡态理论计算出 AAP 与 HO、Cl、NH、ClO、Cl 和 NO 的二级反应速率常数分别为 2.66×10 M s、2.61×10 M s、1.02×10 M s、7.74×10 M s、1.32×10 M s、1.48×10 M s。然后，使用这些二级反应速率常数来区分自由基对 AAP 降解的贡献。通过高分辨率质谱鉴定出 13 种转化产物。结合活性位点和势能面，提出了详细的反应途径。总的来说，这项研究深入了解了活性自由基介导的 AAP 降解机制。
