Formation of Condensation Products in Advanced Oxidation Technologies: The Photocatalytic Degradation of Dichlorophenols on TiO2

Photocatalytic treatment of dichlorophenols (DCPs) leads to the formation of condensation products. These products were identified as polyhydroxyPCBs. Depending on the initial DCP isomer, different extents and yields of polyhydroxyPCB formation (up to 1%) and different types of polyhydroxyPCBs were observed. The formation of dehalogenated hydroxyphenols and hydroxytrichlorobiphenyls in the presence of oxygen suggests that, in addition to oxidative pathways, reductive pathways are also operating. In contrast to direct photolysis by UV irradiation, no evidence of hydroxypolychlorodibenzo-p-dioxins or dibenzofurans was found. PolyhydroxyPCBs are destroyed in the same time window as the initial DCP. The similarities between this photocatalytic process and other advanced oxidation processes (AOP) based on . 0H radical chemistry are discussed.