摘要/Abstract

在低压汞灯（253.7 nm）光照条件下，研究了样品制备过程中引入的有机溶剂甲醇对目标有机物阿特拉津光氧化降解速率的影响规律，并系统地分析了其影响机理.研究结果表明：反应体系中含有低浓度（<0.1%）有机溶剂甲醇时，不会对阿特拉津在单独UV工艺中的降解动力学产生影响；对UV/H₂O₂工艺中阿特拉津降解动力学的影响较小，但此含量的甲醇却能显著地降低阿特拉津在UV/TiO₂工艺中的降解速率.甲醇对阿特拉津在不同光氧化工艺中降解动力学的影响是甲醇与阿特拉津竞争光量子、改变溶液极性和淬灭活性氧化物种等作用的综合结果，但反应体系中甲醇的存在及含量未改变阿特拉津降解产物的种类及降解途径.本研究的结果可为探索溶液制备时引入到反应体系中的有机溶剂对有机目标物光氧化速率的影响提供新的研究视角，同时也能为文献中目标物配制在不同溶剂中的降解速率差异提供合理解释.
关键词: 阿特拉津, 甲醇, 紫外光, 高级氧化工艺, 降解速率, 降解机理
Stock solutions of organic micro-pollutants with low water solubility are commonly prepared using organic solvents in laboratory studies on degradation of these organic compounds. Dilution of the stock solution unavoidably introduces a small amount of organic solvent into the experimental working solutions. This could possibly affect the estimation of the degradation rate constants (k_obs) of these organic micro-pollutants by UV-based oxidation processes. To demonstrate this problem, the effect of organic solvents on the degradation rate of atrazine (ATZ) has been investigated in the sole-UV, UV/H₂O₂ and UV/TiO₂ process at the concentration levels that would likely be derived from stock solutions. Organic solvent methanol (MeOH) commonly used for stock-solution preparation was selected. The degradation of ATZ was investigated under ultraviolet irradiation (253.7 nm). The reaction was conducted in an annular photochemical reactor, in the axis of which a low-pressure mercury lamp (LPUV) was installed. The photon flux into the solution from the LPUV was determined to be at 1.18×10^-7 Einstein/s. A magnetic stirrer was located at the bottom of the reactor to maintain homogeneity of the reacting solution. A thermostatic water recirculation system was used to control the solution temperature at 20±0.5℃. Prior to irradiation, the mercury lamp was ignited for 30 min for a stable output. UV photo-oxidation was performed with ultrapure water containing an initial 0.1 or 5 mg/L ATZ and different volume ratio of methanol. Solution pH value of 4.0, 7.0 and 10.0 was buffered using phosphate or borate. Determination of ATZ using ultra-performance liquid chromatography-electrospray-triple quadrupole mass spectrometry coupled with an ACQUITY^TM UPLC BEH C8 separation column. The results show that the reaction rate of ATZ in UV/TiO₂ process could be affected significantly by the presence of MeOH, even at a concentration well below that possibly introduced during the preparation of working solutions from the organic solvent stock solutions (e.g. 0.01%, V/V). With the increase of MeOH concentration, the k_obs of ATZ in UV/TiO₂ process gradually decreases. The organic solvents having a stronger reaction activity with·OH tend to impose a greater effect on the k_obs of ATZ. However, MeOH does not affect k_obs of photolysis of ATZ in sole-UV process, and a small effect for the k_obs of ATZ in UV/H₂O₂ process. In addition, MeOH in the reaction system does not affect the speciation and degradation pathway of ATZ under different UV-based oxidation processes. The findings here provide a plausible explanation for the discrepancies in the reaction rate constants reported in the literature for some organic micro-pollutants during the UV-based oxidation processes.
Key words: atrazine, methanol, ultraviolet, advanced oxidation process, degradation rate, degradation mechanism


PDF全文下载地址:

点我下载PDF