Key Laboratory of Groundwater Resources and Environment, Ministry of Education, Jilin University, Changchun, 130021, China.
Environ Sci Pollut Res Int. 2019 Oct;26(29):29780-29788. doi: 10.1007/s11356-019-06089-8. Epub 2019 Aug 12.
Since Cr(VI) is highly toxic, the environmental reduction of Cr(VI) to Cr(III) has attracted significant attention. Oxalic acid, a primary component of dissolved organic matter (DOM), is widely distributed throughout the natural environment but the reduction of Cr(VI) by oxalic acid is insignificant at the low concentrations present in the environment; however, the reduction of Cr(VI) is accelerated significantly in ice. In terms of combined pollution, Cr(VI) can coexist with other organic pollutants in the environment but the impact of organic pollutants on the reduction of Cr(VI), changes to the organic pollutants themselves, and the role of oxalic acid in these reactions are unknown. In this study, we investigated redox reactions between Cr(VI) and phenolic compounds in ice (- 15 °C) in the presence of oxalic acid and compared these to room temperature redox reactions in aqueous solutions (20 °C). While these redox reactions were negligible in aqueous solution, they were significantly accelerated in ice under acidic conditions, which was primarily attributed to the freeze concentration effect. Oxalic acid has two functions in these redox reactions; the first is to provide the H required for the reaction and the second is to serve as a reducing agent. When oxalic acid and phenolic pollutants coexist, Cr(VI) preferentially reacts with the phenolic compounds. Phenol, 4-chlorophenol (4-CP), and 2,4-dichlorophenol (2,4-DCP) were each demonstrated to reduce Cr(VI) in ice, but the reaction rate and overall reactivity of these three phenolic compounds are different.
由于 Cr(VI) 毒性很高，因此将其环境还原为 Cr(III) 引起了广泛关注。草酸是溶解有机质 (DOM) 的主要成分，广泛分布于自然环境中，但在环境中存在的低浓度下，草酸对 Cr(VI) 的还原作用并不明显；然而，在冰中，Cr(VI) 的还原作用显著加速。在联合污染方面，Cr(VI) 可以与环境中的其他有机污染物共存，但有机污染物对 Cr(VI) 还原的影响、有机污染物本身的变化以及草酸在这些反应中的作用尚不清楚。在这项研究中，我们研究了在冰（-15°C）中存在草酸时 Cr(VI) 和酚类化合物之间的氧化还原反应，并将其与水溶液（20°C）中的室温氧化还原反应进行了比较。虽然这些氧化还原反应在水溶液中可以忽略不计，但在酸性条件下在冰中显著加速，这主要归因于冻结浓缩效应。草酸在这些氧化还原反应中有两个作用；第一个是提供反应所需的 H，第二个是作为还原剂。当草酸和酚类污染物共存时，Cr(VI) 优先与酚类化合物反应。在冰中，苯酚、4-氯苯酚 (4-CP) 和 2,4-二氯苯酚 (2,4-DCP) 都被证明可以还原 Cr(VI)，但这三种酚类化合物的反应速率和整体反应活性不同。
