MOE Key Laboratory of Deep Earth Science and Engineering, College of Architecture and Environment, Sichuan University, Chengdu 610065, China.
School of Environmental and Safety Engineering, Changzhou University, Changzhou 213164, China.
Environ Sci Technol. 2024 May 14;58(19):8576-8586. doi: 10.1021/acs.est.4c00988. Epub 2024 May 2.
Humic acid (HA) is ubiquitous in natural aquatic environments and effectively accelerates decontamination by permanganate (Mn(VII)). However, the detailed mechanism remains uncertain. Herein, the intrinsic mechanisms of HA's impact on phenolics oxidation by Mn(VII) and its intermediate manganese oxo-anions were systematically studied. Results suggested that HA facilitated the transfer of a single electron from Mn(VII), resulting in the sequential formation of Mn(VI) and Mn(V). The formed Mn(V) was further reduced to Mn(III) through a double electron transfer process by HA. Mn(III) was responsible for the HA-boosted oxidation as the active species attacking pollutants, while Mn(VI) and Mn(V) tended to act as intermediate species due to their own instability. In addition, HA could serve as a stabilizer to form a complex with produced Mn(III) and retard the disproportionation of Mn(III). Notably, manganese oxo-anions did not mineralize HA but essentially changed its composition. According to the results of Fourier-transform ion cyclotron resonance mass spectrometry and the second derivative analysis of Fourier-transform infrared spectroscopy, we found that manganese oxo-anions triggered the decomposition of C-H bonds on HA and subsequently produced oxygen-containing functional groups (i.e., C-O). This study might shed new light on the HA/manganese oxo-anion process.
腐殖酸（HA）在自然水生环境中普遍存在，能有效地促进高锰酸盐（Mn(VII)）的净化。然而，其详细机制仍不确定。在此，系统研究了 HA 对 Mn(VII)及其中间锰氧阴离子氧化酚类物质的内在机制。结果表明，HA 促进了 Mn(VII)中单电子的转移，从而依次形成 Mn(VI)和 Mn(V)。形成的 Mn(V)通过 HA 的双电子转移过程进一步还原为 Mn(III)。Mn(III)是 HA 促进氧化的活性物质，因为它攻击污染物，而 Mn(VI)和 Mn(V)由于自身的不稳定性，倾向于作为中间物种。此外，HA 可以作为稳定剂与生成的 Mn(III)形成配合物，并减缓 Mn(III)的歧化。值得注意的是，锰氧阴离子不会使 HA 矿化，但基本上会改变其组成。根据傅里叶变换离子回旋共振质谱和傅里叶变换红外光谱的二阶导数分析，我们发现锰氧阴离子引发了 HA 上 C-H 键的分解，随后产生了含氧官能团（即 C-O）。本研究可能为 HA/锰氧阴离子过程提供新的见解。
