Meng Zi-He, Wu Song-Hai, Sun Shi-Wei, Xu Zhi, Zhang Xiao-Cong, Wang Xiang-Ming, Liu Yong, Ren Hai-Tao, Jia Shao-Yi, Bai He, Han Xu
School of Chemical Engineering and Technology, Tianjin University, Tianjin, P.R. China.
School of Chemistry and Chemical Engineering, Tianjin University of Technology, Tianjin, P.R. China.
Inorg Chem. 2020 Mar 2;59(5):3171-3180. doi: 10.1021/acs.inorgchem.9b03524. Epub 2020 Feb 20.
The Mn(HCO)-HO (Mn-BAP) system shows high reactivity toward oxidation of electron-rich organic substrates; however, the predominant oxidizing species and its formation pathways involved in the Mn-BAP system are still under debate. In this study, we used the Mn-BAP system to oxidize As(III) in that As(III), Mn, and HCO are common components in As(III)-contaminated groundwater. Kinetic results show that Mn(HCO) [including Mn(HCO) and Mn(HCO)] is a key factor in the Mn-BAP system to oxidize As(III). Quenching experiments rule out contributions of OH and O to As(III) oxidation and reveal that O and the oxidizing species generated from O play predominant roles in the oxidation of As(III). We further reveal that the MnO(HCO) intermediate generated in the reaction between Mn(HCO) and O, instead of O, is the predominant oxidizing species. Although CO also contributes to As(III) oxidation, the high reaction rate constant between CO and O indicates that CO is not the predominant oxidizing species in the As(III)-Mn-BAP system. In addition, the presence of Mn(III) further indicates the important Mn(II)-Mn(III) cycling in the Mn-BAP system. We therefore suggest two important roles of Mn(HCO) in the Mn-BAP system: (i) Mn(HCO) reacts with HO to form the Mn(HCO) intermediate, followed by a subsequent reaction between Mn(HCO) and HO to produce O; (ii) Mn(HCO) can also stabilize O with the formation of MnO(HCO). MnO(HCO) is an electrophilic reagent and plays the predominant role in the oxidation of As(III) to As(V).
Mn(HCO) - HO（Mn - BAP）体系对富电子有机底物的氧化表现出高反应活性；然而，Mn - BAP体系中主要的氧化物种及其形成途径仍存在争议。在本研究中，我们使用Mn - BAP体系氧化As(III)，因为As(III)、Mn和HCO是受As(III)污染地下水中的常见成分。动力学结果表明，Mn(HCO) [包括Mn(HCO) 和Mn(HCO)] 是Mn - BAP体系氧化As(III)的关键因素。猝灭实验排除了OH和O对As(III)氧化的贡献，并揭示O以及由O产生的氧化物种在As(III)的氧化中起主要作用。我们进一步揭示，在Mn(HCO)与O的反应中生成的MnO(HCO)中间体而非O是主要的氧化物种。尽管CO也有助于As(III)的氧化，但CO与O之间的高反应速率常数表明CO不是As(III) - Mn - BAP体系中的主要氧化物种。此外，Mn(III)的存在进一步表明了Mn - BAP体系中重要的Mn(II) - Mn(III)循环。因此，我们提出Mn(HCO)在Mn - BAP体系中的两个重要作用：（i）Mn(HCO)与HO反应形成Mn(HCO)中间体，随后Mn(HCO)与HO发生后续反应生成O；（ii）Mn(HCO)还可以通过形成MnO(HCO)来稳定O。MnO(HCO)是一种亲电试剂，在将As(III)氧化为As(V)的过程中起主要作用。
