Heterogeneous photocatalysis: Degradation of dilute solutions of dichloromethane (CH2Cl2), chloroform (CHCl3), and carbon tetrachloride (CCl4) with illuminated TiO2 photocatalyst

In dilute (10–200 ppm) aqueous solutions, the chloromethanes CCl4, CHCl3, and CH2Cl2 are completely mineralized to CO2 and HCl by the heterogeneous photocatalyst TiO2. The reaction rates in the absence of accumulated product are described by a simple Langmuir form, rate = k · K[chloromethane]1 + K[chloromethane] The relative rate constants are in the approximate ratio of 29 (trichloro-): 9 (dichloro): 1 (tetrachloromethane). Chloride ion inhibits the rate of degradation, as do product protons, as shown by experiments with added initial CsCl or HCl.