光催化技术辅以理论计算模拟水体环境中活性氧物种(ROSs)对典型芳香性农药转化机制的研究

Their presence of organic pesticides in environmental waters, even at trace levels, may adversely affect the aquatic ecosystems and public health. However, it is very difficult to capture their metabolic intermediates of organic pesticides due to the relatively low concentrations and their complicated metabolic pathway, so that the harmful of these metabolites on aquatic ecosystem and human health cannot be evaluated effectively. In this project, we selected the aromatic pesticides with similar molecular structure as the target compounds. And then, with the help of photocatalytic technology, the degradation intermediates and mechanism of these pesticides, attacked by oOH radicals and the other reactive oxygen species (ROSs) in environmental water, will be disscussed. Additionally, the frontier electron densities (FEDs) for aromatic pesticides and transition state of degradation intermediates by Gaussian 09 software will be calculated. By combination of experimental results with theoretical data, the degradation intermediates and mechanism of different kinds of aromatic pesticides will be compared, and the effect of different substituted groups on degradation intermediates and mechanism will be explored. From above-mentioned results, the general transformation law of aromatic pesticides attacked by ROSs will be studied systematically, and the most likely metabolic intermediates and pathway will be deduced in environmental waters. By doing this, their environmental fate, transfer, effect and potential risk of aromatic pesticides can be properly elucidated in environmental waters as well as during water treatment processes.

本项目是针对残留在环境水体中的有机农药的浓度相对较低并且其代谢途径复.杂，难以捕捉其在环境水体中的代谢产物和分析其代谢途径，从而难以有效地研究这些代谢产物对水生生态系统和人类健康的危害等特点，以分子结构类似的芳香性农药为目标化合物，利用光催化技术探讨水体环境中oOH等一系列活性氧物种(ROSs)对这些目标化合物的攻击所产生的降解中间产物和降解途径，并结合Gaussian 09软件对芳香性农药的前线电子云密度（FEDs）及其主要降解中间产物的过渡态理论计算，比较同一类芳香性农药的降解产物和降解途径异同，探讨不同取代基团对芳香性农药降解途径的影响，从而系统地研究具有类似分子结构的芳香性农药在ROSs的作用下降解的一般规律，并推导出其在环境水体中可能的代谢途径，试图为芳香性农药在天然环境水体中的界面迁移、转化、及其光化学降解提供实验和理论依据。

为了探索水体环境中低浓度的有机农药在活性氧物种(ROSs)作用下的迁移转化机制，本项目选取苯胺类、取代脲类、三嗪类等芳香性农药为代表，利用光催化技术和理论计算相结合的手段，着重研究了芳香性农药的降解机制。研究结果表明•OH对芳香性农药的降解占主导作用，其他ROSs的贡献较小，而•OH和芳香性农药的反应主要包括三种类型，即吸氢反应、取代反应和加成反应；并且取代基的变化影响了•OH和芳香性农药之间的反应类型。借助理论计算的结果，运用现代仪器分离分析手段，得出了芳香性农药降解主要产物，并对其反应机制推导。研究发现苯胺类农药在降解过程中的主要途径包括母体化合物的羟基化、醚键的断裂、氯乙酰键的断裂等；取代脲类农药在降解过程中的主要途径为母体化合物的羟基化、芳香环上的官能团被•OH取代、在光生空穴的作用下母体化合物分子中脲桥键上取代基的断裂等；三嗪类农药在降解过程中的主要途径为母体化合物的羟基化、侧链的羟基化以及侧链胺基上基团的断裂等。类似的反应机理，我们在克百威、噻虫嗪和啶虫脒等有机农药的光催化降解过程中均观测到。因此，通过比较研究得出芳香性农药在ROSs作用下一般的迁移转化规律，即芳香环是羟基化的主要活性位点、芳香环上的卤原容易被•OH取代、侧链中的碳杂键容易被攻击而断裂，如C-N、C-O键等。另外，含有杂原子的侧链和芳香环相比具有较高的点电荷，其更容易被吸附而发生反应。在•OH作用下，该共性转化机制的提出为芳香性农药在天然环境水体中的界面迁移、转化、及其光化学降解提供实验和理论依据。