Photodegradation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans: direct photolysis and photocatalysis processes.

This study employed direct photolysis to treat mixed polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) solutions. The solutions included a synthetic standard 17 2, 3, 7, 8-substituted congeners solution and a practical liquid extracted from the bag filter ash of an electric arc furnace. Additionally, this work utilized a coupled catalyst (ZnO/SnO2) under UV irradiation for photocatalytic degradation of 1, 2, 3, 6, 7, 8-HxCDD and OCDD. The direct photolysis rate of PCDFs was faster than that of PCDDs. The degradation rate of international toxicity equivalency quantity (I-TEQ) for PCDDs and PCDFs in the synthetic standard solution was 1.369 and 1.472 h(-1), respectively, and that in the ash-extracted solution was 0.061 and 0.117 h(-1), respectively. The rate of photocatalytic degradation declined as the number of chlorine atoms increased. No 2, 3, 7, 8-substituted congeners were identified during photocatalytic degradation; additionally, the photolytic rate of the UV/coupled catalyst was higher than that of UV/single catalyst system. Experimental results suggested that the primary degradation pathway for direct photolysis and photocatalysis of PCDD/Fs was the CCl cleavage and CO cleavage, respectively.