硝酸根对水中2,4-D光解的影响

Effect of nitrate ion on 2,4-D photodegradation

以300 W汞灯为模拟太阳光光源,在滤去波长小于290 nm光的Pyrex试管中,考察了淡水和海水中不同浓度的硝酸根离子(NO-3)对除草剂2,4-二氯苯氧乙酸(2,4-D)光解动力学的影响,并利用电子顺磁共振技术研究了2,4-D光解过程中羟基自由基(OH)的作用。结果表明,淡水和海水中2,4-D的光解反应均符合一级动力学方程,2,4-D的光解速率随水中NO-3浓度的增高而加快。相同实验条件下,当NO-3初始浓度小于31 mg/L时,海水环境中2,4-D的光解速率常数略高于淡水环境。电子顺磁共振技术证实光照条件下水溶液中NO-3的存在有利于OH的生成,表明2,4-D的降解可能和OH产生的氧化反应有关。

Using a 300 W mercury lamp to simulate sunlight,and in Pyrex tubes restricting the transmission of wavelengths below 290 nm,the photodegradation processes of 2,4-dichlorophenoxyacetic acid（2,4-D） with different concentrations of nitrate ion（NO3^-） in freshwater and seawater were studied,respectively. At the same time,the effect of hydroxyl free radical（＊OH） on the photolysis of 2,4-D was also studied using electron paramagnetic resonance（EPR） technique. The results indicated that the 2,4-D photolysis reaction followed the first order kinetics in freshwater and seawater under different concentrations of NO3^-. Meanwhile,the photochemical reaction rate of 2,4-D increased with the concentration of NO-3increasing. When the concentration of NO3^- was less than 31 mg / L,the photochemical reaction rate of 2,4-D in seawater was higher than that in freshwater slightly at the same experiment conditions. EPR spectra indicated thatOH radicals were generated in the NO-3solution under simulated sunlight irradiation,implying that 2,4-D degradation could be related to oxidation reactions caused byOH.