Environmental Technology ( IF 2.2 ) Pub Date : 2020-11-26 , DOI: 10.1080/09593330.2020.1850876 Naoyuki Kishimoto 1 , Koki Hara 2
ABSTRACT
In recent times, some researchers have successfully demonstrated the efficacy of UV photolysis of electrochemically generate free chlorine (UV/electro-chlorine) as for an advanced oxidation process. Since bromine as well as chlorine is an element belonging to halogen, it is expected that UV photolysis of electrochemically generated free bromine (UV/electro-bromine) also shows an advanced oxidation effect. To elucidate the feasibility of UV/electro-bromine system, its advanced oxidation mechanism was investigated using radical probes of 1,4-dioxane and nitrobenzene. In contrast to the UV/electro-chlorine system, the advanced oxidation effect of UV/electro-bromine system was inhibited under acidic conditions due to the accumulation of photochemically inert Br2. The most abundant radical in UV/electro-bromine system was dibromine radical anion (Br2˙−) and the second-order reaction rate constant of Br2˙− with 1,4-dioxane was estimated to be 2.4 × 105 M−1 s−1. As a result of the abundance and the reactivity of Br2˙−, it was the main contributor to 1,4-dioxane degradation. On the other hand, nitrobenzene was mainly decomposed by direct UV photolysis because Br2˙− does not react with nitrobenzene. The contribution of hydroxyl radical (HO˙) to 1,4-dioxane degradation was much lower than that of Br2˙− because its concentration was 4–5 order of magnitude lower than that of Br2˙−. However, the HO˙ concentration elevated with a decrease in the concentration of bromide ion (Br−). Consequently, the reactivity of Br2˙− with pollutants and the Br− concentration have critical impacts on the advanced oxidation performance of UV/electro-bromine system.
中文翻译:
电化学生成游离溴紫外光解的高级氧化机理
摘要
最近,一些研究人员已经成功地证明了电化学产生游离氯(UV/电氯)的紫外光解作为高级氧化过程的功效。由于溴和氯是属于卤素的元素,因此预计电化学产生的游离溴(UV/电溴)的紫外光解也显示出高级氧化效应。为了阐明紫外/电溴体系的可行性,使用1,4-二恶烷和硝基苯的自由基探针研究了其高级氧化机理。与UV/电氯体系相比,UV/电溴体系的高级氧化效应在酸性条件下由于光化学惰性Br 2的积累而受到抑制。. UV/电溴体系中最丰富的自由基是二溴自由基阴离子(Br 2 ˙ - ),Br 2 ˙ -与1,4-二恶烷的二级反应速率常数估计为2.4 × 10 5 M - 1秒-1。由于 Br 2 ˙ -的丰度和反应性,它是 1,4-二恶烷降解的主要贡献者。另一方面,硝基苯主要通过直接紫外光解分解,因为Br 2 ˙ -不与硝基苯反应。羟基自由基(HO˙)对1,4-二恶烷降解的贡献远低于Br 2˙ -因为它的浓度比 Br 2 ˙ -低 4-5 个数量级。然而,随着溴离子 (Br - )浓度的降低,HO˙ 浓度升高。因此,Br 2 ˙ -与污染物的反应性和Br -浓度对UV/电溴系统的高级氧化性能具有重要影响。