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Metal ions-mediated concerted electron-proton transfer enables catalytic oxidation of phenolic contaminants by permanganate.

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Title: Metal ions-mediated concerted electron-proton transfer enables catalytic oxidation of phenolic contaminants by permanganate.
Authors: Chen, Tiansheng1,2 (AUTHOR), Xie, Pin1 (AUTHOR), Yu, Yanghai1 (AUTHOR), Duan, Xiaoguang3 (AUTHOR), Sun, Yuankui1,4 (AUTHOR) sunyuankui@des.ecnu.edu.cn, Guan, Xiaohong1 (AUTHOR) guanxh@tongji.edu.cn
Source: Water Research. Jan2025:Part A, Vol. 268, pN.PAG-N.PAG. 1p.
Subjects: Metal ions, Catalytic oxidation, Charge exchange, Phenols, Water purification
Abstract: • Metal ions selectively accelerated phenols oxidation by permanganate. • Concerted proton-electron transfer was catalyzed by metal ions. • Permanganate/metal system prefers to attack hydroxyl O site of phenols. • The enhancement effect of metal ions correlates with their complexing capability. Permanganate has been extensively applied in water treatment due to its ease of handling and high stability. However, the impact of common water constituents, especially metal ions, on permanganate oxidation is poorly understood. Here, we report that many redox-inactive metal ions, such as Ca2+, Mg2+, Zn2+, Cu2+, and Al3+, can enhance the reactivity of permanganate with phenolic compounds. Moreover, the enhancing effects of metal ions are highly pH-dependent with the largest promotion effect obtained at the pH close to phenols' p K a. Experimental and computational analysis revealed that the oxidation of protonated phenols by permanganate underwent proton-coupled electron transfer (PCET) pathways, regardless of the presence of metal ions. Nonetheless, metal ions could catalyze the concerted electron-proton transfer (CEPT) but exhibited negligible effect on ETPT (electron transfer followed by proton transfer) and PTET (proton transfer followed by electron transfer) reactions, accounting for the pH-dependent effects of metal ions. Correlation between CEPT rate constants and the complexing capability of metal ions with phenols suggested that the co-existing metal ions may coordinate to phenolic O–H group and thus facilitate the CEPT reaction of phenols. This study could shed light on the application of permanganate in real practice and the modulation of CEPT reactions. [Display omitted] [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:• Metal ions selectively accelerated phenols oxidation by permanganate. • Concerted proton-electron transfer was catalyzed by metal ions. • Permanganate/metal system prefers to attack hydroxyl O site of phenols. • The enhancement effect of metal ions correlates with their complexing capability. Permanganate has been extensively applied in water treatment due to its ease of handling and high stability. However, the impact of common water constituents, especially metal ions, on permanganate oxidation is poorly understood. Here, we report that many redox-inactive metal ions, such as Ca2+, Mg2+, Zn2+, Cu2+, and Al3+, can enhance the reactivity of permanganate with phenolic compounds. Moreover, the enhancing effects of metal ions are highly pH-dependent with the largest promotion effect obtained at the pH close to phenols' p K a. Experimental and computational analysis revealed that the oxidation of protonated phenols by permanganate underwent proton-coupled electron transfer (PCET) pathways, regardless of the presence of metal ions. Nonetheless, metal ions could catalyze the concerted electron-proton transfer (CEPT) but exhibited negligible effect on ETPT (electron transfer followed by proton transfer) and PTET (proton transfer followed by electron transfer) reactions, accounting for the pH-dependent effects of metal ions. Correlation between CEPT rate constants and the complexing capability of metal ions with phenols suggested that the co-existing metal ions may coordinate to phenolic O–H group and thus facilitate the CEPT reaction of phenols. This study could shed light on the application of permanganate in real practice and the modulation of CEPT reactions. [Display omitted] [ABSTRACT FROM AUTHOR]
ISSN:00431354
DOI:10.1016/j.watres.2024.122622