Comparative study of heterogeneous photocatalytic decomposition of tetrachloroethene and trichloroethene in the gas phase Original Research Article

The effects of the initial concentrations of the substrates, oxygen and water vapor were studied in the heterogeneous photocatalytic decompositions of tetrachloroethene (PCE) and trichloroethene (TCE). The amounts of substrate and oxygen in the reaction mixture were found to play important roles in the degradation, while the effect of water vapor was negligible. The intermediates dichloroacetyl chloride and trichloroacetyl chloride accelerate the transformations of both substrates; vice versa in the absence of the initial substrates, the decomposition of the acetyl chloride derivatives are very slow. The proposed reaction mechanism includes some differences from that previously described; the results suggest that the initiation step is the recombination of species formed by direct charge transfer from the excited semiconductor to the substrate. The formation of the measured intermediates and products is associated with the appearance of oxy- and superoxy-radicals. The proposed, detailed mechanism is in good accordance with the distributions of the analyzed products and their reaction kinetic behavior.