典型来源腐殖酸不同光敏结构的分离与识别及对水中持久性有毒物质光解的影响机理研究

Humic acids (HA) are the most widely distributed macromolecular organic matter in the natural multimedia environment, influencing the transfer and transformation of organic pollutants significantly. In natural aquatic systems, photochemical processes are important pathways for the transformation of persistent toxic substances (PTS) that are poorly biodegradable. The vast diversity in structural components of HA might be key factors accounting for their different photochemical behavior. Considering that HA originated from different sources has its own unique photosensitive molecular structure, the project is designed to extract HA from typical areas of Northeast such as Changbai mountain forests in Jilin, prairies in inner Mongolia, brown coal in Heilongjiang, and Liaohe River in Liaoning, select the appropriate template according to the different forming environment to separate photosensitive fractions from HA of different origins using molecular imprinting technique, characterize the photosensitive structures in detail, and study the photochemical formation of reactive oxygen species (ROS) according to photodegradation of PTS in aqueous solutions in the presence of photosensitive components or their complex with metals. The study would further reveal the relationships between the photochemical activity of HA, the specific photosensitive structure of HA and their forming environment from molecular dimensions. The study is of significance and scientific value on understanding the photosensitive structures of HA existing in different environmental media correctly and the ecological risk of persistent toxic pollutants.

腐殖酸是广泛存在于自然界各种环境介质的一种大分子有机质，对环境污染物的迁移转化具有重要影响。光解是天然水体中难以生物降解的持久性有毒物质迁移转化的重要过程。腐殖酸复杂的结构特点是影响腐殖酸光化学行为的一个关键因素。本申请项目针对"不同来源的腐殖酸具有自己独特的光敏分子结构"的科学问题，拟从东北典型地区如吉林长白山森林、内蒙古大草原、黑龙江褐煤、辽宁辽河水系等，进行腐殖酸的提取，利用分子印迹技术根据不同的形成环境选择合适的模板分子，进行不同来源腐殖酸中光敏组分的分离，对印迹的光敏结构进行详细表征和识别；通过水中持久性有毒污染物的光解实验，研究腐殖酸光敏组分及其金属络合物存在下活性氧化物种的形成消失规律，进而从分子尺寸上揭示腐殖酸光化学活性和腐殖酸具体光敏结构及其形成环境之间的关系。本项研究对正确认识不同环境介质中腐殖酸的光敏结构及持久性有毒污染物的生态风险性具有重要意义和科学价值。

采用分子印迹技术对不同来源腐殖酸中具有光化学活性的特定结构进行分离，成功分离出了腐殖酸中具有类核黄素的、类叶绿素的、类醌类的外伸π-共轭大环结构的组分，这些组分具有较高的吸光强度和较多的酸性官能团。腐殖酸光敏化产生的羟基自由基（•OH）、三重态腐殖酸（3HA*）和单线态氧（1O2）是阿特拉津、2,4-D和双酚A光降解的主要原因。将污染物的光降解速率常数k与不同来源腐殖酸的光学性质(E2/E3、E4/E6和 A254)进行耦合分析，发现k与A254成反比，与E2/E3成正比；E4/E6比值越低，HA的芳香度越高，k越大，光敏性越强。测定了腐殖酸不同光敏级分光照过程中产生的1O2的稳态浓度和3HA*的量子产率，发现不同来源的腐殖酸的光敏活性具有一定的差异，其中光敏活性大小为：来源于河流底泥腐殖酸>来源于森林土壤腐殖酸>来源于草原土腐殖酸。这些内容的研究为从本质上掌握腐殖酸的环境行为及典型有机污染物在地表水中的光解过程机理奠定一定基础。