Photocatalytic Degradation of Polychlorinated Dibenzo-p-dioxins on TiO2 Film under UV or Solar Light Irradiation

The photocatalytic degradation of polychlorinated dibenzo-p-dioxins (PCDDs), which include mono-, tetra-, hepta-, and octachlorinated congeners (MCDD, TCDD, HpCDD and OCDD), was carried out on TiO2 films under UV (λ > 300 nm) or solar light irradiation in the air. All the dioxin congeners tested were successfully degraded on TiO2 while the direct photolysis of them in the absence of TiO2 was negligible. The photocatalytic degradation rates of PCDDs decreased with the number of chlorines and were described by the first-order reaction kinetics with half-lives of 5.8, 3.9, 0.71, and 0.38 h for OCDD, HpCDD, TCDD, and MCDD, respectively. The degradation rates increased with light intensity and TiO2 coating weights up to 2 mW/cm2 (300 < λ < 400 nm) and 200 μg of TiO2/cm2, respectively. Further increases in either the light intensity or the TiO2 coating mass did not much affect the degradation rate. The natural solar light under clear sky conditions was as effective as a 200-W mercury lamp irradiation (filtered ...