| 초록 |
The photocatalytic degradation of polychlorinated dibenzo-p-dioxins (PCDDs), whichinclude mono-, tetra-, hepta-, and octachlorinated congeners (MCDD, TCDD, HpCDDand OCDD) was carried out on TiO2 films under UV or solar light irradiation in the air.All the PCDD congeners tested were successfully degraded on TiO2 while the directphotolysis of them in the absence of TiO2 was negligible. The photocatalyticdegradations of PCDDs were well described by the first-order reaction kinetics withhalf-lives of 6.9, 4.6, 1.5 and 0.42 hrs for OCDD, HpCDD, TCDD, and MCDD,respectively. The photocatalytic degradation rates of PCDDs exponentially decreasedwith the number of substituted Cl atoms. The slower degradation rates of the highlychlorinated PCDDs are ascribed to the lack of unsubstituted carbons that are vulnerableto an OH radical attack. The natural solar light under a clear sky condition was aseffective as a 200 W mercury lamp irradiation (filtered through a Pyrex filter) indegrading OCDD on TiO2. The initial pathway of the photocatalytic degradation ofPCDDs is presumed to be an OH radical attack. From a diffuse reflectance FTIRstudy, the degradation of OCDD was found to involve the cleavage of the aromatic ringof OCDD with the accompanying appearance of the aliphatic C=C- bond. No stableintermediates or no less chlorinated PCDDs were detected during the photocatalyticdegradation.
|
