Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 18 Shuang-qing Road, Beijing, 100085, China.
Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 18 Shuang-qing Road, Beijing, 100085, China.
Water Res. 2018 Oct 15;143:109-116. doi: 10.1016/j.watres.2018.06.026. Epub 2018 Jun 15.
Quinone group is an important fraction of humic acid. The pseudo-first-order rate constant (k) of levofloxacin (LF) degradation by permanganate (MnO) significantly increased from 0.010 (without benzoquinone, BQ) to 0.042-0.443 min at [BQ]:[MnO] (molar ratio) = 0.03-0.25 at pH 7.5, and an acidic pH facilitated LF degradation. In the presence of BQ, MnO was first reduced to Mn(II). Then, Mn(II) reacted with BQ to produce Mn(III) and semiquinone radical, which was promoted under acidic conditions. With dissolved oxygen available, Mn(III) further oxidized semiquinone radical to produce singlet oxygen (O) and superoxide radical (O) as well as regenerate BQ. In addition, MnO could also react with Mn(II) to produce Mn(III), whose complexation with semiquinone radical in turn promoted this reaction. Due to the predominant scavenging of O by BQ, O and Mn(III) mainly contributed to the accelerated LF degradation, with a notable formation of hydroxyl, ketone and endoperoxide groups in the degradation byproducts. This study helps better understand the role of natural organic matter in the degradation of organic micropollutants by MnO in water treatment.
醌基团是腐殖酸的重要组成部分。在 pH 7.5 条件下，[BQ]：[MnO]（摩尔比）为 0.03-0.25 时，锰酸钾（MnO）对左氧氟沙星（LF）的降解一级速率常数（k）从 0.010（无苯醌，BQ）显著增加到 0.042-0.443 min，酸性条件有利于 LF 的降解。在 BQ 的存在下，MnO 首先还原为 Mn(II)。然后，Mn(II)与 BQ 反应生成 Mn(III)和半醌自由基，在酸性条件下得到促进。有溶解氧存在时，Mn(III)进一步将半醌自由基氧化为单线态氧（O）和超氧自由基（O），并再生 BQ。此外，MnO 还可以与 Mn(II)反应生成 Mn(III)，其与半醌自由基的络合又促进了这一反应。由于 O 主要被 BQ 猝灭，因此 O 和 Mn(III)主要促进 LF 的加速降解，在降解产物中形成了大量的羟基、酮基和内过氧化物基团。本研究有助于更好地理解天然有机物在水处理中 MnO 降解有机微量污染物中的作用。
