多氟代二苯并对二噁英(PFDDs)的光降解动力学及机理研究

As typical fluorine-containing and dioxin-like compounds, polyfluorinated dibenzo-p-dioxins (PFDDs) have been detected in the environment, and they may pose significant toxicity effects on organisms. In this study, 18 structure representative PFDDs with different fluorine substitution are selected as target compounds to explore their transformation behaviors in simulated solar irradiation, natural irradiation and UV/persulfate system. The influence of solvent, light intensity, inorganic ions, and pH of the reaction solution were systematically studied, and QSAR models between molecular structural parameters/the number and position of fluorine substitution and photodegradation rate constants were established to reveal the main molecular descriptors affecting the reaction rate. Modern analytical techniques such as LC-MS, GC-MS and NMR were used to identify the intermediate products, which were further interpreted by frontier electron density calculations and transition state theory using Gaussian program. Based on the theoretical calculation and experimental results, the photodegradation pathways and reaction mechanisms of PFDDs was proposed. Studies on the photodegradation reactions of PFDDs are very important, which will provide basis and reference information for the transformation, fate and removal of PFDDs in the environment.

多氟代二苯并对二噁英(PFDDs)是一类“类二噁英”物质，存在于环境中，并有显著的生物毒性。本研究以本课题组已合成的18种氟原子取代数目不同、结构上有代表性的PFDDs系列化合物为研究对象，研究其在模拟光降解、自然光降解和UV/过硫酸盐联合降解体系中的转化行为。考察溶剂性质、光照强度、无机离子以及pH值等反应条件对PFDDs降解速率的影响，建立其分子结构参数/取代位置参数和降解速率常数之间的QSAR模型，从分子层面探究影响其转化速率的主要因素；采用LC-MS、GC-MS以及核磁共振技术等分析鉴定反应的中间产物，使用Gaussian程序计算PFDDs的前线电荷密度和反应的过渡态，将理论计算与实验结果相结合，提出PFDDs的光解反应途径与反应机理。探索PFDDs发生光降解的难易程度及其光反应机理，可为实际环境中这类化合物的转化、归趋和去除研究提供理论支撑和实际指导。

多氟代二苯并对二噁英(PFDDs)是一类“类二噁英”物质，存在于环境中，并有显著的生物毒性。本研究以本课题组已合成的18种氟原子取代数目不同、结构上有代表性的PFDDs系列化合物为研究对象，研究其在直接光照和光氧化体系中的转化行为。发现PFDDs在正己烷中的直接光解符合准一级动力学模型，氟原子取代数目越多的PFDDs分子，其光解速度越慢。建立了PFDDs光解速率的QSAR模型，氟原子取代数目和位置以及C-O键键长是影响PFDDs直接光解速率的主要因素。对比不同光氧化体系，发现Fe(II)联合UV/PMS可实现对八氟代二苯并对二噁英(OFDD)的高效降解，溶液pH值、碳酸氢根离子、氯离子以及腐殖酸等环境因素都会影响OFDD在UV/Fe(Ⅱ)/PMS体系中的降解速率，SO4−•和HO•在反应体系中均存在，对OFDD的降解起着重要作用。PFDDs在二氧化硅上的光解速率常数(ksilica)和在正己烷中的光解速率常数(khexane)之间存在良好的线性关系，但是由于二氧化硅体系中还存在羟基自由基引发的反应，ksilica值大于khexane值。采用LC-MS和GC-MS技术鉴定了三个体系的降解产物，结合量子化学计算，推测了相应的光化学转化路径，发现PFDDs可通过羟基取代、C-O键断裂和电子转移反应生成羟基化PFDDs(OH-PFDDs)、羟基化多氟联苯醚(OH-PFDEs)和氟代苯酚，通过耦合消除反应生成三元和四元环化合物。通过研究PFDDs在不同光反应体系中发生降解的难易程度及其反应机理，可为实际环境中这类化合物的转化、归趋和去除提供理论支撑和实际指导。