Chain photoreduction of CCl3F induced by TiO2 particles

Fluorotrichloromethane (CFC 11) is, dehalogenated. through a reductive chai n reaction upon illumination of aqueous, air-free suspensions of TiO2 parti cles in the presence of formate ions. The reduction takes place with large photonic efficiencies at pH greater than or equal to 5 even at high photon fluxes, producing mainly Cl- and dichlorofluoromethane (HCFC 21), while F- is only a minor byproduct. In the proposed mechanism (CO2-)-C-. and (CCl2F) -C-. radicals are the chain carriers, Cl- as well as HCFC 21 result from pr opagation steps, and cross-termination of the chain carriers forms F-., Sim ple steady-state assumptions, that regard propagations as the, dominant ste ps, yield kinetic equations consistent with the data of the initial fast Cl - formation step. The subsequent evolution of rates and postirradiation eff ects are consequences of the slow removal of electrons from the semiconduct or.