Effect of pH and molar ratio of pollutant to oxidant on a photochemical advanced oxidation process using hypochlorite
Effect of pH and molar ratio of pollutant to oxidant on a photochemical advanced oxidation process using hypochlorite
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DOI：
10.1080/09593330.2015.1034187
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发表时间：
2015-10-02
影响因子：
2.8
通讯作者：
Nishimura, Hideya
中科院分区：
文献类型：
--
作者：
Kishimoto, Naoyuki;Nishimura, Hideya
紫外线(UV)-光解过氧化氢(H_2O_2)是一种传统的高级氧化工艺(AOP)，尽管H_2O_2的成本很高，但它具有简单的优点。因此，我们尝试用次氯酸盐代替H_2O_2在光化学AOP中，并以1，4-二氧六环为模型污染物，讨论了pH值和污染物与次氯酸盐的摩尔比对该过程的影响。在不同pH值下，在254 nm波长处对次氯酸盐溶液进行的光化学处理表明，次氯酸(HOCl)物种的紫外光分解主要是产生羟基自由基(中心点OH)。反应效率以脱除的1，4-二氧六环与消耗的次氯酸盐的摩尔比表示，在较高的pH水平下，由于次氯酸根离子(ClO-)对自由基的清除作用比HOCl2强，反应效率变差。次氯酸盐作为AOP紫外光降解的最适pH范围为3-6。在初始1，4-二氧六环与初始次氯酸盐的摩尔比较高的情况下，反应效率超过100%，这是由于光化学生成的氯自由基(中心点Cl)再生了HOCl.最后，根据与氯物种有关的自由基反应，提出了HOCl紫外光解的总体反应，即1 mmo1 mmoL的HOCl光解化学计量生成2 mmo1 mmoL的中心点OH。由于液氯的使用比H_2O_2更经济，从化学计量和化学成本的角度来看，在光化学AOP中用H_2O_2取代H_2O_2是可行的。
Ultra violet (UV)-photolysis of hydrogen peroxide (H2O2) is a conventional advanced oxidation process (AOP) and is advantageous in its simplicity, although H2O2 is costly. Accordingly, we tried to substitute H2O2 by hypochlorite in the photochemical AOP, and discussed the effect of pH and the molar ratio of a pollutant to hypochlorite on the process using 1,4-dioxane as a model pollutant. The photochemical treatment of hypochlorite solutions at a wavelength of 254 nm under various pH values revealed that the UV-photolysis of hypochlorous acid (HOCl) species mainly contributed to hydroxyl radical (center dot OH) production. The reaction efficiency, as defined by the molar ratio of removed 1,4-dioxane to consumed hypochlorite, deteriorated under higher pH levels due to the stronger radical scavenging effect of hypochlorite ion (ClO-) as compared to that of HOCl. The optimal pH for the UV-photolysis of hypochlorite as an AOP was found to be in the range of 3-6. The reaction efficiency at a high molar ratio of initial 1,4-dioxane to initial hypochlorite exceeded 100%, which was caused by the regeneration of HOCl from photochemically generated chlorine radicals (center dot Cl). Finally, the overall reaction of the UV-photolysis of HOCl was proposed on the basis of the radical reactions that were related to chlorine species, which suggested that the UV-photolysis of 1 mmol of HOCl stoichiometrically produced 2 mmol of center dot OH. Since the use of liquid chlorine is more economical than that of H2O2, the substitution of HOCl for H2O2 in the photochemical AOP was concluded to be feasible from the viewpoints of both stoichiometry and chemical costs.