Formation of Dichlorine Monoxide for Organic Pollutant Degradation by Free Chlorine in High Chloride-Containing Water,ACS ES&T Water

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Formation of Dichlorine Monoxide for Organic Pollutant Degradation by Free Chlorine in High Chloride-Containing Water
ACS ES&T Water ( IF 4.8 ) Pub Date : 2023-01-15 , DOI: 10.1021/acsestwater.2c00477
Chuanjing Lin ₁ , Li Ling _{1,

2} , Chii Shang _{1,

3}

Affiliation

Several ppm levels of free chlorine in high chloride-containing water of no less than 0.20 M show remarkably high degradation rate constants toward carbamazepine (k_CBZ′). Dichlorine monoxide (Cl₂O) was identified to be responsible for the high k_CBZ′. Cl₂O degrades aromatic pollutants connected to more electron-donating functional groups faster when comparing k_Cl₂O to 1,4-dimethoxybenzene, bisphenol A, benzoic acid, and CBZ. However, its formation at low free chlorine levels in high chloride-containing water cannot be explained by our current knowledge. We proposed an alternative Cl₂O formation mechanism, in which chloride transforms hypochlorous acid/hypochlorite (HOCl/ClO^–) to dichlorine (Cl₂) and polychloride monoanions (Cl_n^–), which then react with HOCl/ClO^– to form Cl₂O. Decreasing pH from 8.60 to 4.33 increases Cl₂ concentrations and thus generates about 600× higher Cl₂O concentrations. Weak acid anions, for example, phosphate and bicarbonate, are strong nucleophiles assisting the Cl₂O hydrolysis, but their presence at the testing conditions does not much affect k_CBZ′. The proposed alternative Cl₂O formation mechanism reveals the roles of chloride in shifting the equilibrium toward the Cl₂O formation, allowing the simple chlorine addition strategy to degrade recalcitrant organic pollutants in high chloride-containing wastewater. It may also change our understanding of the speciation of different free chlorine species and their impacts on the DBP formation in high chloride-containing wastewater.

中文翻译：

高氯水中游离氯降解有机污染物生成一氧化二氯

在不低于 0.20 M 的高氯化物水中，几个 ppm 水平的游离氯显示出对卡马西平的非常高的降解速率常数 ( k _CBZ ')。一氧化二氯 (Cl ₂ O) 被确定是造成高k _CBZ ' 的原因。_{与 1,4-二甲氧基苯、双酚 A 、}苯甲酸和 CBZ相比， Cl ₂_O可以更快地降解与更多供电子官能团相连的芳香族污染物_{_。}然而，我们目前的知识无法解释它在高含氯水中的低游离氯水平下的形成。我们提出了另一种 Cl ₂O 形成机制，其中氯化物将次氯酸/次氯酸盐 (HOCl/ClO ^– ) 转化为二氯 (Cl ₂ ) 和多氯单阴离子 (Cl _n^– )，然后与 HOCl/ClO ^–反应形成 Cl ₂ O。降低 pH 值8.60 至 4.33 增加了 Cl ₂浓度，因此产生了约 600 倍高的 Cl ₂ O 浓度。弱酸性阴离子，例如磷酸盐和碳酸氢盐，是有助于Cl _{2 O水解的强亲核试剂，但它们在测试条件下的存在对}k _CBZ '影响不大。提议的替代品 Cl ₂O 形成机制揭示了氯化物在使平衡向 Cl ₂ O 形成方向移动中的作用，允许简单的氯添加策略来降解高氯废水中的顽固有机污染物。它还可能改变我们对不同游离氯物种的形态及其对高氯废水中 DBP 形成的影响的理解。

更新日期：2023-01-15

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