Abstract
Effects of the sonication before UV irradiation on the rate of photocatalytic mineralization of some chlorinated organic comopounds in oxygen saturated aqueous solutions were examined using the pre-treated titanium dioxide (P25) of which suspensions were sonicated for 1 hour before use. The enhancement effect on the photocatalytic mineralization by the pre-sonolysis was not observed for the most of the chlorinated organic compounds examined here such as dichloroethane, chloroacetic acids, chloromethanes, trichloroethylene and tetrachloroethylene except trichloroacetic acid and tetrachloromethane. These results indicate that the sonolysis before the photo-irradiation does not always promoto the further oxidation to mineralization by the following photocatalysis. For trichloroacetic acid and tetrachloromethane, however, the pre-sonolysis enhanced the photocatalytic mineralization significantly. Both compounds are known to be resistive to the photocatalytic degradation, because they have no hydrogen atom to be abstracted by the OH radicals generated on the TiO_2 particles by the photo-irradiation since that reaction is generally considered to be the initiation step of the photocatalytical degradation of organic compounds. The. pre-sonolysis effect for these compounds would be caused by the formation of some products sonochemically at first, perhaps a partly dechlorinated compounds. Once these products are formed, they are oxidized rapidly further to carbon dioxide and chloride ion by the following photocatalytic reactions.
