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.

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。