College of Environmental Sciences and Engineering, Peking University, The Key Laboratory of Water and Sediment Sciences, Ministry of Education, Beijing, 100871, China.
College of Environmental Sciences and Engineering, Peking University, The Key Laboratory of Water and Sediment Sciences, Ministry of Education, Beijing, 100871, China.
Environ Pollut. 2023 Sep 1;332:121987. doi: 10.1016/j.envpol.2023.121987. Epub 2023 Jun 9.
Current density was the key factor that impacted pollutant degradation by electrochemical oxidation, and reaction contributions at various current densities were non-negligible for the cost-effective treatments of organic pollutants. This research introduced compound specific isotope analysis (CSIA) into atrazine (ATZ) degradation by boron doped diamond (BDD) with current density of 2.5-20 mA/cm, in order to provide "in-situ" and "fingerprint" analysis of reaction contributions with changed current densities. As results, the increased current density displayed a positive impact on ATZ removal. The Ʌ values (correlations of ΔδC and ΔδH) were 24.58, 9.18 and 8.74 when current densities were 20, 4, and 2.5 mA/cm, with ·OH contribution of 93.5%, 77.2% and 80.35%, respectively. While DET process favored lower current density with contribution rates up to ∼20%. What's more interesting, though the carbon and hydrogen isotope enrichment factors (ε and ε) were fluctuate, the Ʌ linearly increased accompanied with applied current densities. Therefore, increasing current density was effective due to the larger ·OH contribution even though side reactions may occur. DFT calculations proved the increase of C-Cl bond length and the delocalization of Cl atom, confirming dechlorination reaction mainly occurred in the direct electron transfer process. While ·OH radical mainly attack the C-N bond on the side chain, which was more benefit to the fast decomposition of ATZ molecule and intermediates. It was forceful to discuss pollutant degradation mechanism by combining CSIA and DFT calculations. Target bond cleavage (i.e., dehalogenation reaction) can be conducted by changing reaction conditions like current density due to the significantly different isotope fractionation and bond cleavage.
电流密度是影响电化学氧化降解污染物的关键因素，在不同电流密度下的反应贡献对于有机污染物的经济有效处理是不可忽视的。本研究将化合物特定同位素分析（CSIA）引入到电流密度为 2.5-20 mA/cm 的掺硼金刚石（BDD）降解莠去津（ATZ）中，以提供不同电流密度下反应贡献的“原位”和“指纹”分析。结果表明，增加电流密度对 ATZ 的去除有积极影响。当电流密度分别为 20、4 和 2.5 mA/cm 时，Ʌ 值（ΔδC 和 ΔδH 的相关性）分别为 24.58、9.18 和 8.74，·OH 贡献分别为 93.5%、77.2%和 80.35%。而 DET 过程则有利于较低的电流密度，贡献率高达约 20%。更有趣的是，尽管碳和氢同位素富集因子（ε和ε）波动，但Ʌ 随施加电流密度线性增加。因此，尽管可能会发生副反应，但增加电流密度会由于较大的·OH 贡献而有效。DFT 计算证明了 C-Cl 键长的增加和 Cl 原子的离域化，证实了脱氯反应主要发生在直接电子转移过程中。而·OH 自由基主要攻击侧链上的 C-N 键，这更有利于 ATZ 分子及其中间产物的快速分解。通过结合 CSIA 和 DFT 计算来讨论污染物降解机制是有力的。由于同位素分馏和键断裂的显著差异，可以通过改变电流密度等反应条件来进行目标键的断裂（即脱卤反应）。
