Impact of humic acid on the degradation of levofloxacin by aqueous permanganate: Kinetics and mechanism.
Impact of humic acid on the degradation of levofloxacin by aqueous permanganate: Kinetics and mechanism.
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DOI：
10.1016/j.watres.2017.06.037
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发表时间：
2017-10
期刊：
影响因子：
12.8
通讯作者：
Ke Xu;Weiwei Ben;Wencui Ling;Yu Zhang;J. Qu;Z. Qiang
中科院分区：
文献类型：
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作者：
Ke Xu;Weiwei Ben;Wencui Ling;Yu Zhang;J. Qu;Z. Qiang
左氧氟沙星(LF)是地表水中常见的氟喹诺酮类药物，高锰酸盐(MnO4-−)是饮用水处理中常用的氧化剂。从动力学和机理两方面考察了腐植酸(HA)对水相MnO4-−降解LF的影响。在无HA的条件下，测定了MnO4-−在pH 7.5时降解LF的二级速率常数(K)为3.9M−1s−1，并随pH的降低而增大。在HA存在下，当[HA]o：[KMnO4]o(质量比)=0.50时，LF降解的准一级速率常数(Kobs)分别增加3.8倍和2.8倍。二次氧化剂清除和电子顺磁共振测试表明，HA能与MnO4-−与HA反应产生的强氧化中间体Mn(III)形成络合物，诱导超氧自由基(O2·点−)和羟基自由基(点·OH)的连续生成。由此产生的自由基dotOH主要是导致LF加速降解的主要原因，而络合物[HA-Mn(III)]可以解释其余的加速。在MnO4-−氧化过程中，LF及其副产物的降解主要通过羟化、脱氢和羧化三种途径进行，HA的存在对LF的破坏作用更强。本研究有助于更好地了解MnO4−在饮用水处理中对有机微污染物的降解作用。
Levofloxacin (LF) is a frequently detected fluoroquinolone in surface water, and permanganate (MnO4−) is a commonly used oxidant in drinking water treatment. This study investigated the impact of humic acid (HA) on LF degradation by aqueous MnO4−from both kinetic and mechanistic aspects. In the absence of HA, the second-order rate constant (k) of LF degradation by MnO4−was determined to be 3.9 M−1s−1at pH 7.5, which increased with decreasing pH. In the presence of HA, the pseudo-first-order rate constant (kobs) of LF degradation at pH 7.5 was significantly increased by 3.8- and 2.8-fold at [HA]o:[KMnO4]o(mass ratio) = 0.5 and 1, respectively. Secondary oxidant scavenging and electron paramagnetic resonance tests indicated that HA could form a complex with Mn(III), a strongly oxidative intermediate produced in the reaction of MnO4−with HA, to induce the successive formation of superoxide radicals (O2radical dot−) and hydroxyl radicals (radical dotOH). The resulting radical dotOH primarily contributed to the accelerated LF degradation, and the complex [HA-Mn(III)] could account for the rest of acceleration. The degradation of LF and its byproducts during MnO4−oxidation was mainly through hydroxylation, dehydrogenation and carboxylation, and the presence of HA led to a stronger destruction of LF. This study helps better understand the degradation of organic micropollutants by MnO4−in drinking water treatment.