School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Republic of Singapore; Water Research Analytical Laboratories, Water Quality Office, Public Utilities Board, 82 Toh Guan Road East, #04-03, Singapore 608576, Republic of Singapore.
Water Research Analytical Laboratories, Water Quality Office, Public Utilities Board, 82 Toh Guan Road East, #04-03, Singapore 608576, Republic of Singapore.
Water Res. 2014 Feb 1;49:275-85. doi: 10.1016/j.watres.2013.11.039. Epub 2013 Dec 3.
Photodegradation of 6 iodinated trihalomethanes (ITHMs) under UV irradiation at 254 nm was investigated in this study. ITHMs underwent a rapid photodegradation process through cleavage of carbon-halogen bond with first-order rate constants in the range of 0.1-0.6 min(-1). The effects of matrix species including nitrate, humic acid (HA), bicarbonate, sulfate, and chloride were evaluated. The degradation rate increased slightly in the presence of nitrate possibly due to generation of HO at a low quantum yield via direct photolysis of nitrate, while HA lowered the photodegradation rate of ITHMs due to its competitive UV absorption. Moreover, bicarbonate, sulfate, and chloride had no significant effect on photodegradation kinetics, as there is no UV absorption for these 3 species. In the study using surface water, treated water, and secondary effluent from a wastewater treatment plant, high turbidity and natural organic matters present in the water inhibited the photodegradation of ITHMs. The degradation rates of 6 ITHMs in UV/H2O2 system were rather comparable and significantly higher than those achieved in the UV system without H2O2. To develop a quantitative structure-reactivity relationship (QSAR) model, the logarithm of measured first-order rate constants was correlated with a number of molecular descriptors. The best correlation was obtained with a combination of 3 molecular descriptors, namely the bond strength of carbon-halogen to be broken in the rate-determining step, steric and electronic effects of all substituents to the carbon center.
本研究考察了 254nm 紫外光照射下 6 种碘代三卤甲烷（ITHMs）的光降解情况。ITHMs 通过碳卤键的断裂经历了快速的光降解过程，一级速率常数范围在 0.1-0.6min(-1)之间。评估了包括硝酸盐、腐殖酸（HA）、碳酸氢盐、硫酸盐和氯化物在内的基质种类的影响。在硝酸盐存在下，降解速率略有增加，这可能是由于硝酸盐通过直接光解以低量子产率生成 HO，而 HA 则由于其对 UV 吸收的竞争而降低了 ITHMs 的光降解速率。此外，碳酸氢盐、硫酸盐和氯化物对光降解动力学没有显著影响，因为这 3 种物质没有 UV 吸收。在使用地表水、处理水和废水处理厂二级出水的研究中，水中存在的高浊度和天然有机物抑制了 ITHMs 的光降解。6 种 ITHMs 在 UV/H2O2 体系中的降解速率相当，明显高于在没有 H2O2 的 UV 体系中达到的降解速率。为了开发定量结构-反应性关系（QSAR）模型，将实测一级速率常数的对数与多个分子描述符相关联。与 3 个分子描述符的组合（即速率决定步骤中要断裂的碳卤键的键强度、所有取代基对碳原子的空间和电子效应）获得了最佳相关性。
