State Key Laboratory of Pollution Control and Resource Reuse, School of Environment, Nanjing University, Nanjing 210023, P. R. China.
Department of Environmental Sciences, The Connecticut Agricultural Experiment Station, New Haven, Connecticut 06511, United States.
Environ Sci Technol. 2022 May 17;56(10):6621-6630. doi: 10.1021/acs.est.1c08796. Epub 2022 May 3.
The homogeneous Fe-catalyzed Fenton reaction remains an attractive advanced oxidation process for wastewater treatment, but sustaining the Fe(III)/Fe(II) redox cycle at a convenient pH without the costly input of energy or reductants remains a challenge. Mn(II) is known to accelerate the Fenton reaction, yet the mechanism has never been confidently established. We report a systematic kinetic and spectroscopic investigation into Mn(II) acceleration of atrazine or 2,4,6-trichlorophenol degradation by the picolinic acid (PICA)-assisted Fenton reaction at pH 4.5-6.0. Mn(II) accelerates Fe(III) reduction, superoxide radical (HO/O) formation, and hydroxyl radical (HO) formation. A Mn(II/III)-HO redox cycle as an independent source of reactive oxygen species, as proposed in the literature, is shown to be insignificant. Rather, Mn(II) assists by participating directly and catalytically in the Fe(III)/Fe(II) redox cycle. Initially, Mn(II) (as Mn(PICA)) complexes with a ferric hydroperoxo species, PICA-Fe-OOH. The resulting binuclear complex undergoes intramolecular electron transfer to give Fe(II), which later generates HO from HO, plus MnO, which later decomposes to HO/O (an Fe(III) reductant) and Mn(II), completing the catalytic cycle. This scheme may apply to other Fenton-type systems that go through an Fe-OOH intermediate. The findings here will inform the design of practical and sustainable Fenton-based AOPs employing Mn(II) in combination with chelating agents.
均相 Fe 催化 Fenton 反应仍然是一种有吸引力的废水处理高级氧化工艺，但在无需昂贵的能源或还原剂输入的情况下，在方便的 pH 值下维持 Fe(III)/Fe(II)氧化还原循环仍然是一个挑战。已知 Mn(II)可以加速芬顿反应，但该机制从未得到过明确的证实。我们报告了在 pH 值为 4.5-6.0 时，用吡啶甲酸（PICA）辅助的芬顿反应，对 Mn(II)加速莠去津或 2,4,6-三氯苯酚降解的系统动力学和光谱学研究。Mn(II)加速了 Fe(III)的还原、超氧自由基（HO/O）的形成和羟基自由基（HO）的形成。Mn(II/III)-HO 氧化还原循环作为文献中提出的活性氧物种的独立来源，被证明并不重要。相反，Mn(II)通过直接参与 Fe(III)/Fe(II)氧化还原循环来协助反应。最初，Mn(II)（作为 Mn(PICA)) 与铁过氧氢物种，PICA-Fe-OOH 形成配合物。所得双核配合物发生分子内电子转移，生成 Fe(II)，后者随后从 HO 生成 HO，加上 MnO，后者随后分解为 HO/O（一种 Fe(III)还原剂）和 Mn(II)，完成催化循环。该方案可能适用于其他经历 Fe-OOH 中间体的芬顿型系统。这里的发现将为设计实用和可持续的基于芬顿的 AOPs 提供信息，这些 AOPs 采用 Mn(II)与螯合剂结合使用。
