Redox Conversion of Arsenite and Nitrate in the UV/Quinone Systems
Redox Conversion of Arsenite and Nitrate in the UV/Quinone Systems
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紫外/醌系统中亚砷酸盐和硝酸盐的氧化还原转化
DOI：
10.1021/acs.est.8b03538
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发表时间：
2018
影响因子：
11.4
通讯作者：
Zhang Shujuan
中科院分区：
文献类型：
--
作者：
Chen Zhihao;Jin Jiyuan;Song Xiaojie;Zhang Guoyang;Zhang Shujuan
超氧阴离子自由基（O2·-）是否是砷（As（III））光化学氧化过程中的关键反应物种一直是一个有争议的问题。以对苯二酚（BQH 2）和1，4-苯醌（BQ）为氧化还原介质，研究了As（III）的光化学氧化和NO3-的还原。O2·-、单线态氧（1 O2）、H2 O2和半醌自由基（BQH·）都是辐照体系中可能的反应物种。然而，由于As（IV）的形成是As（III）氧化的必要步骤，考虑到标准还原电位，上述物种与As（III）之间的反应在化学上是不利的。在自由基清除实验的基础上，证明了羟基自由基（·OH）是导致UV/BQH 2体系氧化As（III）的关键物种。·OH自由基是由H_2O_2光解产生的，H_2O_2光解产生的·OH自由基来自O_2·-的反硝化和O_2·-与BQH_2的反应。在UV/BQH 2过程中，NO3-的还原反应主要是由1（BQH 2）* 的光电子发射和3（BQH 2）* 的直接电子转移引起的。在As（III）和NO3-的氧化还原转化中没有观察到协同效应，进一步证明BQH·在所研究的体系中的作用可以忽略不计。研究结果有助于更好地了解醌类化合物在水环境中的光化学行为。
Whether superoxide radical anion (O2•–) was a key reactive species in the oxidation of arsenite (As(III)) in photochemical processes has long been a controversial issue. With hydroquinone (BQH2) and 1,4-benzoquinone (BQ) as redox mediators, the photochemical oxidation of As(III) and reduction of nitrate (NO3–) was carefully investigated. O2•–, singlet oxygen (1O2), H2O2, and semiquinone radical (BQH•) were all possible reactive species in the irradiated system. However, since the formation of As(IV) is a necessary step in the oxidation of As(III), taking the standard reduction potentials into account, the reactions between the above species and As(III) were thermodynamically unfavorable. On the basis of radical scavenging experiments, hydroxyl radical (•OH) was proved as the key species that led to the oxidation of As(III) in the UV/BQH2system. It should be noted that the•OH radicals were generated from the photolysis of H2O2, which came from the disproportionation of O2•–and the reaction of O2•–with BQH2. Both the photoejectedeaq–from1(BQH2)* and the direct electron transfer with3(BQH2)* contributed to the reduction of NO3–in the UV/BQH2process. No synergistic effect was observed in the redox conversion of As(III) and NO3–, further demonstrating that the role of BQH•was negligible in the studied systems. The results here are helpful for a better understanding of the photochemical behaviors of quinones in the aquatic environment.