【作者】 刘欣华；

【导师】 施周；

【作者基本信息】 湖南大学 ， 市政工程， 2006， 硕士

【摘要】 多氯联苯(PCBs)是一类广泛分布的环境有机污染物。其理化性质稳定,且抗生物降解,但它可被紫外光所降解。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的光化学反应在非极性溶剂中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’-四氯联苯在羟丙基-β-环糊精(HPCD)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波段逐渐发生红移。据此可以初步推论2,2’,4,4’-CB在HPCD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(2或2’位)氯原子优先脱除。利用气相色谱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’-三氯联苯及Cl-,并且在降解初期,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。通过动力学试验分析发现,2,2’,4,4’-四氯联苯的光量子产率为0.1291±0.0260,其动力学方程Rate=-dC/dt=kC= 0.0154C.在整个光降解过程中,HPCD可以提供PCBs脱氯反应所需的氢原子,并通过其空腔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。由于在半小时内仅有15%的HPCD被光降解,因此在光降解实践中HPCD可以重复使用以降低成本,其自身为自然界微生物代谢产物,也证明其应用不会造成而次污染。更多还原

【Abstract】 Polychlorinated biphenyls (PCBs) are wildly distributed environmental contaminants. Though they are physically and chemically stable and generally recalcitrant to biodegradation, they are photodegradable. Characteristics and pathways of photodegradation of polychlorinated biphenyls (PCBs) in various solutions are reviewed. Dechlorination in nonpolar solvents was attributed to the main pathway for PCB photolysis. In addition, hydroxylation was the minor pathway for PCB photolysis in polar solvents such as water and alcohols. The photo-reactivity of PCBs was related to the position and quantity of chlorines on the PCB congeners. The application of photolysis in remediation of PCB contaminated soils is also briefly reviewed.Photolysis of 2,2’,4,4’-tetrachlorobiphenyl dissolved in hydroxypropyl–β-cyclodextrin(HPCD) solutions was studied. Under UV irradiation at 254 nm, 2,2’,4,4’-tetrachlorobiphenyl was decomposed. By measuring UV-VIS spectra of photolyzed samples, it has been found that theκband of spectra shifted red as photolysis time increased, which implied a possible stepwise dechlorination with preferential removal of the ortho (2 or 2’)chlorines. Less chlorinated PCB (2,4,4’-trichlorobiphenyl) as well as chloride, were identified as the photoproducts of the tested PCB using a GC-ECD. At the start of photolysis, excellent mass balance existed between 2,2’,4,4’CB and its products. These results indicated that stepwise dechlorination initiated at ortho chlorine was the main photodegradation pathway of the tested PCB congener. After analysis of kenetic of photolysis, quantum yields of the tested 2,2’4,4’-CB was 0.1291±0.0260, and the formula of kenetic of photolysis was Rate = - dC/dt= kC = 0.0154C.By serving as H-atom donor in dechlorination and providing a non-polar solvent environment for dechlorination inside the HPCD cavity, HPCD enhanced photolysis. Only 15% HPCD were decomposed during harf hour photolysis, and unable secondary pollution because of origin from metabolism product from nature microorganism, suggesting HPCD could be reused during photolysis practice in order to reduce the cost.更多还原