2-甲基-4-氯苯氧乙酸及其脱氯产物的光化学降解

紫外消毒工艺作为废水/给水处理的重要步骤，不仅可以有效控制水中的病原体，而且可使废水或水源水中存在的一些污染物发生化学降解作用，但目前对这一作用过程的研究尚不完善。本文针对一种典型的除草剂——2-甲基-4-氯苯氧乙酸（MCPA）及其脱氯产物二甲基苯氧乙酸（MPA），研究了两者在紫外灯照射下的光化学行为，并进一步考察了波长、初始pH值、H2O2及水中其他共存物质对MCPA和MPA光降解效率的影响。研究结果表明，不同光源对MCPA的光降解速率大小为：254 nm波长紫外灯 > 365 nm波长紫外灯 > 可见光灯；低pH值不利于MCPA的光降解，但对MPA光降解的影响不大；在溶液中加入H2O2，会增大MCPA和MPA的光降解速率；MCPA的光降解过程符合一级动力学方程；腐殖酸（HA）会降低MCPA的光降解速率；MPA与MCPA呈现相似的光降解效应，但反应速率比MCPA略快，且在两者共存状态下会降低MCPA的光降解速率。

Photodegradation of 2-methyl-4-chlorophenoxyacetic acid and its dechlorination product

As an important process in waste/feedwater treatment, ultraviolet (UV) disinfection can not only effectively control levels of pathogens in water, but can also degrade some of the pollutants in the wastewater or source water. However, research on the process is not enough. In this paper, the photochemical degradation of a typical herbicide (2-methyl-4-chlorophenoxy acetic acid, MCPA) and its dechlorinated product (2-methylphenoxy acetic acid, MPA) was studied under UV light irradiation, and the effects of wavelength, pH, H2O2, and coexisting substances on the degradation of MCPA and MPA were investigated. The results showed that for the degradation rate of MCPA, UV light with a wavelength of 254 nm > UV light with wavelength of 365 nm > visible light;a low solution pH was unfavorable to the degradation of MCPA, but not to MPA;the degradation rate of MCPA and MPA increased with the addition of H2O2;humic acid (HA) was able to reduce the photodegradation rate of MCPA;MPA exhibited photodegradation behavior similar to that of MCPA, but a faster rate than MCPA, and it was able to decrease the degradation rate of MCPA in the mixture.