Guangdong Provincial Key Laboratory of Water Quality Improvement and Ecological Restoration for Watersheds, School of Ecology, Environment and Resources, Guangdong University of Technology, Guangzhou 510006, China.
School of Civil and Transportation Engineering, Guangdong University of Technology, Guangzhou 510006, Guangdong, China.
Environ Sci Technol. 2024 Feb 27;58(8):4019-4028. doi: 10.1021/acs.est.3c10703. Epub 2024 Feb 17.
Humic acid (HA) ubiquitously existing in aquatic environments has been reported to significantly impact permanganate (KMnO) decontamination processes. However, the underlying mechanism of the KMnO/HA system remained elusive. In this study, an enhancing effect of HA on the KMnO oxidation of diclofenac (DCF) was observed over a wide solution pH range of 5-9. Surprisingly, the mechanism of HA-induced enhancement varied with solution pH. Quenching and chemical probing experiments revealed that manganese intermediates (Mn(III)-HA and MnO) were responsible for the enhancement under acidic conditions but not under neutral and alkaline conditions. By combining KMnO decomposition, galvanic oxidation process experiments, electrochemical tests, and FTIR and XPS analysis, it was interestingly found that HA could effectively mediate the electron transfer from DCF to KMnO in neutral and alkaline solutions, which was reported for the first time. The formation of an organic-catalyst complex (i.e., HA-DCF) with lower reduction potential than the parent DCF was proposed to be responsible for the accelerated electron transfer from DCF to KMnO. This electron transfer likely occurred within the complex molecule formed through the interaction between HA-DCF and KMnO (i.e., HA-DCF-KMnO). These results will help us gain a more comprehensive understanding of the role of HA in the KMnO oxidation processes.
腐殖酸（HA）普遍存在于水环境中，据报道，它会显著影响高锰酸盐（KMnO）的消毒过程。然而，KMnO/HA 体系的潜在机制仍不清楚。在这项研究中，HA 对 5-9 宽溶液 pH 范围内的二氯芬酸（DCF）的 KMnO 氧化表现出增强效应。令人惊讶的是，HA 诱导增强的机制随溶液 pH 而变化。猝灭和化学探测实验表明，在酸性条件下，锰中间体（Mn(III)-HA 和 MnO）负责增强，但在中性和碱性条件下则不然。通过结合 KMnO 分解、电偶氧化过程实验、电化学测试以及 FTIR 和 XPS 分析，有趣的是发现，HA 可以在中性和碱性溶液中有效地介导 DCF 向 KMnO 的电子转移，这是首次报道。提出形成比母体 DCF 还原电势更低的有机催化剂配合物（即 HA-DCF）负责加速 DCF 向 KMnO 的电子转移。这种电子转移可能发生在通过 HA-DCF 和 KMnO 之间的相互作用形成的复合物分子内（即 HA-DCF-KMnO）。这些结果将帮助我们更全面地了解 HA 在 KMnO 氧化过程中的作用。
