Abstract：
Peracetic-acid-based advanced oxidation processes (PAA-AOPs) on metal-free catalysts have emerged as charming strategies for water contaminant removal. However, the involved reactive species and their corresponding active sites are ambiguous. Herein, using carbon nanotube (CNT) as a model carbocatalyst, we demonstrated that, under neutral conditions, the CNT-PAA* complex was the dominant reactive species to oxidize phenolic compounds via electron-transfer process (ETP), whereas the surface-bound hydroxyl radicals (·OHsurface) played a minor role on the basis of quenching and electrochemical tests as well as Raman spectroscopy. More importantly, the experimental and density functional theory (DFT) calculation results collaboratively proved that the active site for ETP was the sp2-hybridized carbon on the CNT bulk, while that for radical generation was the edge-located hydroxyl group (C-OH), which lowered the energy barrier for cleaving the O-O bond in CNT-PAA* complex. We further discerned the oxidation kinetic constants (koxid) of different pollutants from the apparent kinetic constants in CNT/PAA system. The significant negative linear correlation between lnkoxid and half-wave potential of phenolic compounds suggests that the pollutants with a lower one-electron oxidation potential (i.e., stronger electron-donating ability) are more easily oxidized. Overall, this study scrutinizes the hybrid radical and non-radical mechanism and the corresponding active sites of the CNT/PAA system, providing insights into the application of PAA-AOPs and the development of ETP in the remediation of emerging organic pollutants.
摘要：
在无金属催化剂上基于过乙酸的高级氧化工艺（PAA-AOPs）已成为去除水污染物的迷人策略。然而,所涉及的反应性物种及其相应的活性位点是模糊的。在这里，使用碳纳米管（CNT）作为模型碳催化剂，我们证明了，在中性条件下,CNT-PAA*络合物是通过电子转移过程（ETP）氧化酚类化合物的主要反应性物种，而表面结合的羟基自由基（·OHsurface）在猝灭和电化学测试以及拉曼光谱的基础上起着次要作用。更重要的是,实验和密度泛函理论（DFT）计算结果共同证明，ETP的活性位点是CNT本体上的sp2杂化碳，虽然自由基生成是位于边缘的羟基（C-OH），这降低了CNT-PAA*复合物中裂解O-O键的能垒。我们从CNT/PAA系统中的表观动力学常数进一步辨别了不同污染物的氧化动力学常数（koxid）。酚类化合物的lnkoxid与半波电位之间的显着负线性相关表明，具有较低的单电子氧化电位的污染物（即，更强的给电子能力)更容易被氧化。总的来说,这项研究审查了混合自由基和非自由基机制和相应的活性位点的CNT/PAA系统，提供对PAA-AOPs的应用和ETP在新兴有机污染物修复中的发展的见解。
