阴离子表面活性剂（SDS）溶液中PCBs的光降解研究

【作者】 王政华；

【导师】 施周；

【作者基本信息】 湖南大学 ， 市政工程， 2002， 硕士

【摘要】 多氯联苯(PCBs)是一类广泛分布的环境污染物，其理化性质稳定，且抗生物降解，但它可以被紫外光所降解。本文综述了PCBs在各种溶剂中的紫外光化学反应和降解途径：PCBs的光化学反应以氢取代氯的脱氯反应为主，除此之外，在水和醇等极性溶液中，还存在羟基化反应；PCBs的光化学反应活性与其氯原子数量和取代位置有关。另外，还简述了光降解在治理受PCBs污染土壤方面的应用。在前人研究的基础上，本文对2，2’，4，4’．四氯联苯在阴离子表面活性剂(十二烷基硫酸钠)胶束溶液中的光降解进行了研究。在紫外光(254nm)辐照下，四氯联苯被降解。通过对各个时段光解试样的紫外--可见吸收光谱的检测，发现随光解时间的增加其吸收光谱中的K波段逐渐发生蓝移。据此可以初步推论2，2’，4，4’-CB在SDS溶液中的光化学反应可能是一个逐步脱氯的降解过程，且苯环上的邻位氯原子优先脱除。利用气相色谱、气相色谱--质谱联用仪和氯离子选择电极对试样做进一步检测确定光解产物为含氯量较少的多氯联苯：2，4，4’-三氯联苯、4，4’-二氯联苯、4-氯联苯及C1-，并且2，2’，4，4’-四氯联苯与其产物之间存在很好的质量平衡关系。以上结果表明，从邻位氯原子开始的逐步脱氯反应为所试四氯联苯的主要光解途径。在整个光降解过程中，表面活性剂可以提供PCBs脱氯反应所需的氢原子，并通过形成胶束来提供脱氯反应所需的非极性溶剂环境，从而强化了多氯联苯的光降解效果。而且仅有6％的表面活性剂在1小时内被光降解，因此在光降解实践中表面活性剂可以重复使用以降低成本。更多还原

【Abstract】 Polychlorinated biphenyls (PCBs) are wildly distributed environmentalcontaminants. Though they are physically and chemical1y stable and generallyrecalcitrant to biodegradation, they are photodegradable. Characteristics andpathways of photodegradation of polychlorinated biphenyls (PCBs) in varioussolutions are reviewed. Dechlorination was attributed to the main pathway forPCB photolysis. In addition, hydroxylation was the minor pathway for PCBphotolysis in polar solvents such as water and alcohols. The photo-reactivity ofPCBs was related to the position and quantity of chlorines on the PCB congeners.The application of photolysis in remediation of PCB contaminated soils is alsobriefly reviewed.Photolysis of 2,2’,4,4’-tetrachlorobiphenyl dissolved in anionic surfactant(sodium dodecyl sulfate) micellar solutions was studied. Under UV irradiation at254 nm, 2,2’,4,4’-tetrachlorobiphenyl was decomposed. By measuring UV-VISspectra ofphotolyzed samples, it has been found that the K band of spectra shiftedblue as photolysis time increased, which implied a possible stepwisedechlorination with preferential removal of the ortho chlorines. Less chlorinatedPCB congeners (2,4,4’-trichlorobiphenyl, 4,4’-dichlorobiphenyl, 4-chlorobiphenyl)as well as chloride, were identified as the photoproducts of the tested PCB usinga GC-ECD, a GC-MS as well as a chloride selective electrode respectively.Excellent mass balance existed between 2,2’,4,4’CB and its products. Theseresults indicated that stepwise dechlorination initiated at ortho chlorine was themain photodegradation pathway of the tested PCB congener.By serving as H-atom donor in dechlorination and providing a non-polarsolvent environment fOr dechlorination inside the surfactant micelles, surfactantenhanced photolysis. Only 6% surfactants were decomposed during one hourphotolysis, suggesting surfactants could be reused during photolysis practice inorder to reduce the cost.更多还原