Kishimoto Naoyuki, Nishimura Hideya
a Faculty of Science and Technology , Ryukoku University , Otsu , Japan.
Environ Technol. 2015;36(19):2436-42. doi: 10.1080/09593330.2015.1034187. Epub 2015 Apr 21.
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 (•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 (•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 •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.
过氧化氢（H₂O₂）的紫外光解是一种传统的高级氧化工艺（AOP），尽管H₂O₂成本高昂，但该工艺具有操作简单的优势。因此，我们尝试在光化学AOP中用次氯酸盐替代H₂O₂，并以1,4 - 二氧六环作为模型污染物，探讨了pH值和污染物与次氯酸盐的摩尔比对该工艺的影响。在不同pH值下对次氯酸盐溶液进行254 nm波长的光化学处理表明，次氯酸（HOCl）的紫外光解是产生羟基自由基（•OH）的主要原因。由去除的1,4 - 二氧六环与消耗的次氯酸盐的摩尔比定义的反应效率，在较高pH值下会降低，这是因为与HOCl相比，次氯酸根离子（ClO⁻）具有更强的自由基清除作用。作为AOP的次氯酸盐紫外光解的最佳pH值范围为3 - 6。当初始1,4 - 二氧六环与初始次氯酸盐的摩尔比很高时，反应效率超过100%，这是由光化学产生的氯自由基（•Cl）使HOCl再生所致。最后，基于与氯物种相关的自由基反应，提出了HOCl紫外光解的总体反应，这表明1 mmol HOCl的紫外光解按化学计量会产生2 mmol的•OH。由于使用液氯比使用H₂O₂更经济，从化学计量和化学成本两个角度来看，在光化学AOP中用HOCl替代H₂O₂被认为是可行的。
