Guo Ruixue, Qi Yumeng, Li Beibei, Tian Jie, Wang Zunyao, Qu Ruijuan
State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing, Jiangsu, China 210023.
State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing, Jiangsu, China 210023.
Water Res. 2022 Nov 1;226:119316. doi: 10.1016/j.watres.2022.119316.
As a class of emerging aquatic pollutants, alkylimidazole-based ionic liquids (AM-ILs) have received extensive attention due to the large acute toxicity to aquatic organisms. Therefore, in order to protect both aquatic organisms and human beings, it is necessary to seek an efficient and environmental-friendly technology for removal of AM-ILs from water bodies. In this work, we found that under simulated sunlight (Xe lamp) irradiation, periodate (KIO, PI) could efficiently degrade 1-hexyl-2,3-dimethylimidazolium bromide ([HMMIm]Br), a representative AM-ILs with six carbon atoms in the side chain. Kinetics experiments on the degradation of [HMMIm]Br were performed, and the results showed that a high degradation efficiency (≥90.00%) of the cation ([HMMIm]) was still maintained under harsh water conditions of strong acidity/alkaliny or with various non-target inorganic ions. More importantly, the anion of bromide ion (Br) was not oxidized to the carcinogenic bromate (BrO) in current reaction system. The excited stated PI (marked as PI*) was detected by Laser flash photolysis, and it was an important reactive species for [HMMIm] degradation. As rationalized by theoretical calculations and scavenging experiments, the main oxidation mechanisms of [HMMIm] were hydroxyl radicals induced substitution reaction, PI* initiated electron and double oxygen transfer, and direct photolysis mediated chemical bond cleavage reaction, which contributed to 73%, 21%, and 6% of [HMMIm] degradation, respectively. Moreover, toxicity evaluation by ECOSAR software indicated that the oxidation products were generally less toxic to three aquatic organisms (fish, water flea, and green algae) than the target molecule [HMMIm]Br. In conclusion, this work proposed novel oxidation mechanisms of sunlight-activated PI system, and the findings may inspire further researches on the application of photoactivated hypervalent acids in water purification.
作为一类新兴的水体污染物，基于烷基咪唑的离子液体（AM - ILs）因其对水生生物具有较大的急性毒性而受到广泛关注。因此，为了保护水生生物和人类，有必要寻求一种高效且环保的技术来从水体中去除AM - ILs。在这项工作中，我们发现，在模拟太阳光（氙灯）照射下，高碘酸盐（KIO，PI）能够有效降解1 - 己基 - 2,3 - 二甲基咪唑溴盐（[HMMIm]Br），这是一种侧链含有六个碳原子的代表性AM - ILs。对[HMMIm]Br的降解进行了动力学实验，结果表明，在强酸性/碱性或含有各种非目标无机离子的苛刻水体条件下，阳离子（[HMMIm]）仍保持较高的降解效率（≥90.00%）。更重要的是，在当前反应体系中，溴离子（Br⁻）的阴离子并未被氧化成致癌的溴酸盐（BrO₃⁻）。通过激光闪光光解检测到激发态的PI（标记为PI*），它是[HMMIm]降解的重要活性物种。经理论计算和清除实验分析，[HMMIm]的主要氧化机制为羟基自由基诱导的取代反应、PI*引发的电子和双氧转移以及直接光解介导的化学键断裂反应，它们分别对[HMMIm]降解的贡献为73%、21%和6%。此外，通过ECOSAR软件进行的毒性评估表明，氧化产物对三种水生生物（鱼类、水蚤和绿藻）的毒性通常低于目标分子[HMMIm]Br。总之，这项工作提出了太阳光活化PI体系的新型氧化机制，这些发现可能会激发对光活化高价酸在水净化中的应用的进一步研究。
