The Impact of pH and Irradiation Wavelength on the Production of Reactive Oxidants during Chlorine Photolysis
The Impact of pH and Irradiation Wavelength on the Production of Reactive Oxidants during Chlorine Photolysis
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DOI：
10.1021/acs.est.8b07225
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发表时间：
2019-04-16
影响因子：
11.4
通讯作者：
Remucal, Christina K.
中科院分区：
文献类型：
--
作者：
Bulman, Devon Manley;Mezyk, Stephen P.;Remucal, Christina K.
氯光解是一种高级氧化过程，它依赖于游离有效氯（即次氯酸和次氯酸盐）的光解裂解产生羟基自由基，以及臭氧和一套卤素自由基。尽管氯吸收太阳光谱中的光，但波长对活性氧化剂产生的影响知之甚少。本研究利用活性氧化剂定量、验证探针化合物和动力学建模相结合的方法，研究了氯光解过程中活性氧化剂的形成与pH（6-10）和照射波长（254、311和365 nm）的关系。由于次氯酸盐的摩尔吸收率较高（pK(a) = 7.5），在高波长照射下氯的损失率常数随pH值的增加而增加，而在254 nm处没有变化。在所有测试波长下，羟基自由基和氯自由基的稳态浓度在酸性条件下最大，在254和311 nm照射下最高。在所有条件下都观察到臭氧的产生，在311和365 nm的pH值为8时最大累积浓度。一个全面的动力学模型通常预测氯损失和氧化剂浓度的趋势，但是与先前发表的动力学模型的比较揭示了建模这个复杂系统的挑战。
Chlorine photolysis is an advanced oxidation process which relies on photolytic cleavage of free available chlorine (i.e., hypochlorous acid and hypochlorite) to generate hydroxyl radical, along with ozone and a suite of halogen radicals. Little is known about the impact of wavelength on reactive oxidant generation even though chlorine absorbs light within the solar spectrum. This study investigates the formation of reactive oxidants during chlorine 0 photolysis as a function of pH (6-10) and irradiation wavelength (254, 311, and 365 nm) using a combination of reactive oxidant quantification with validated probe compounds and kinetic modeling. Observed chlorine loss rate constants increase with pH during irradiation at high wavelengths due to the higher molar absorptivity of hypochlorite (pK(a) = 7.5), while there is no change at 254 nm. Hydroxyl radical and chlorine radical steady-state concentrations are greatest under acidic conditions for all tested wavelengths and are highest using 254 and 311 nm irradiation. Ozone generation is observed under all conditions, with maximum cumulative concentrations at pH 8 for 311 and 365 nm. A comprehensive kinetic model generally predicts the trends in chlorine loss and oxidant concentrations, but a comparison of previously published kinetic models reveals the challenges of modeling this complex system.