2,4-二氯苯氧基乙酸的光转化化学发光机理研究

摘要

实验发现,2,4-二氯苯氧基乙酸(2,4-D)经紫外光转化后与KMnO4在H2SO4介质中反应可产生化学发光.采用液相色谱质谱联用技术( LC-MS)对2,4-D光降解产物进行分析,推断光降解主要生成了多酚类降解产物,如2-氯对苯二酚(CHQ)和4-氯邻苯二酚等.化学发光光谱研究发现,2,4-D经紫外光转化后,与KMnO4反应的发光波长为690 nm,与2,4-D的典型降解产物CHQ的化学发光光谱一致.此发光现象是氧化还原过程中生成的Mn(Ⅱ)吸收反应所释放出的化学能成为激发态,再返回基态时产生的特征辐射峰.该反应体系可用于2,4-D的检测,当2,4-D浓度在0.01～10 mg/L范围内与发光强度呈良好的线性关系；检出限为3.0 μg/L.%After irradiation by low pressure mercury lamp, the photoproducts of 2 , 4-dichlorophenoxyacetic acid (2,4-D) could react with KMnO4 to produce strong chemiluminescence (CD in sulfuric acid medium. Liquid chromatography-mass spectrometric (LOMS) analysis of photoproducts reveals that polyphenol products such as chlorohydroquinone(CHQ) and 4-chlorocatechol are produced in the photo reaction. These products can be readily oxidized by KMnO4 to produce light emission with a maximum wavelength at 690 nm. The photoinduced CL spectrum of 2,4-D is in good accordance with that obtained from the typical degradation product CHQ. A CL mechanism related to Mn(Ⅱ) was proposed to elucidate the light emmision process. An excited state Mn (H) is formed in the oxidation reaction, which gives off the extra energy in form of red light when it returns to the ground state. The photoinduced CL reaction can be used for the detection of 2,4-D. Under the optimized reaction conditions, the CL-emission responses linearly to 2,4-D in the range of 0. 01 -10 mg/L with a limit of detection as low as 3. 0 mg/L.