The Research On Photolysis Of PCBs In Hydroxypropyl-β-cyclodextrin Solution

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.