Data for: Reactivity of bromine radical with dissolved organic matter moieties and monochloramine: effect on bromate formation during ozonation

Bromine radical (Br) has been hypothesized to be a key intermediate of bromate formation during ozonation. Once formed, Br further reacts with ozone to eventually form bromate. However, this reaction competes with the reaction of Br with dissolved organic matter (DOM), of which reactivity and reaction mechanisms are less studied to date. To fill this gap, this study determined the second-order rate constant (k) of the reactions of selected organic model compounds, a DOM isolate, and monochloramine (NH2Cl) with Br using γ-radiolysis. The kBr of all model compounds were high (kBr > 108 M-1 s-1) and well correlated with quantum-chemically computed free energies of activation, indicating a selectivity of Br toward electron-rich compounds, governed by electron transfer. The reaction of phenol (a representative DOM moiety) with Br yielded p-benzoquinone as a major product with a yield of 59% per consumed phenol, suggesting an electron transfer mechanism. Finally, the potential of NH2Cl to quench Br was tested based on the fast reaction (kBr, NH2Cl = 4.4 × 109 M-1 s-1, this study), resulting in reduced bromate formation of up to 77% during ozonation of bromide-containing lake water. Overall, our study demonstrated that Br quenching by NH2Cl can substantially suppress bromate formation, especially in waters containing low DOC concentrations (1-2 mgC/L).

溴自由基（Bromine radical, Br）被认为是臭氧化（ozonation）过程中溴酸盐（bromate）生成的关键中间产物。一旦生成，溴自由基会进一步与臭氧反应，最终生成溴酸盐。然而，该反应会与溴自由基和溶解性有机质（dissolved organic matter, DOM）的反应形成竞争，目前针对该类反应的反应活性与反应机制的研究仍相对不足。为填补这一研究空白，本研究采用γ辐解（γ-radiolysis）法，测定了所选有机模式化合物、一种溶解性有机质提取物以及一氯胺（monochloramine, NH₂Cl）与溴自由基的二级速率常数（second-order rate constant, k）。所有模式化合物的kBr值均较高（kBr > 10⁸ M⁻¹·s⁻¹），且与量子化学计算得到的活化自由能具有良好的相关性，表明溴自由基对富电子化合物具有选择性，该选择性由电子转移过程主导。以苯酚（phenol，典型DOM组分）与溴自由基的反应为例，其主要产物为对苯醌（p-benzoquinone），每消耗1mol苯酚的产物得率可达59%，这一结果印证了电子转移反应机制。最后，本研究基于一氯胺与溴自由基的快速反应（kBr,NH₂Cl = 4.4 × 10⁹ M⁻¹·s⁻¹），测试了一氯胺淬灭溴自由基的潜力；结果显示，在含溴化物（bromide）湖水的臭氧化过程中，溴酸盐生成量可被最高抑制77%。综上，本研究证实，通过一氯胺淬灭溴自由基可显著抑制溴酸盐的生成，尤其适用于溶解性有机碳（dissolved organic carbon, DOC）浓度较低（1~2 mgC/L）的水体。