HETEROGENEOUS PHOTOCHEMICAL-REACTIONS BETWEEN VOLATILE CHLORINATED HYDROCARBONS (TRICHLOROETHENE AND TETRACHLOROETHENE) AND TITANIUM-DIOXIDE

Heterogeneous photochemical reactions of trichloroethene (C2HCl3) and tetrachloroethene (C2Cl4) on titanium dioxide (TiO2) were investigated. Both C2HCl3 and C2Cl4 were rapidly transformed to COCl2 and were mineralized to Cl2, HCl or CO2 on TiO2 under photoillumination at room temperature. CO and CHCl3 were formed from C2HCl3 alone and CCl4 from C2Cl4 alone. The decay rates of C2HCl3 and C2Cl4 as well as the formation rates of products varied with reaction conditions of relative humidity, light intensity and concentrations of C2HCl3, C2Cl4 or O2. C2HCl3 and C2Cl4 displayed roughly the same decay rate under dry conditions. Under humid conditions, the reaction rates decreased, particularly for C2Cl4. In the heterogeneous photochemical reactions, O2-, Cl and OH are considered the active chemical species, from analogy with the data reported for the gas-phase and liquid-phase reactions.