The photoinduced decomposition of trichloroethylene adsorbed on Ca-montmorillonite by long-wavelength UV irradiation has been studied in a quartz tube open to air or through which air or oxygen is passed. Solid-sample and liquid-solution NMR techniques were used to identify apparent products or intermediates of the photodecomposition. Dichloroacetic acid was identified as a major organic product/intermediate; substantial amounts of pentachloroethane and trichloroacetic acid were also identified. The formation of CO sub(2) was characterized quantitatively by wet chemical analysis. About 40 and 57, respectively, of the total carbon of trichloroethylene was converted to carbon dioxide in air and O sub(2) environments over a period of 16 days. Phosgene and HCl were also detected. The photodecomposition of trichloroethylene adsorbed on whole soil, on Zn super(2+)-exchanged and Cu super(2+)-exchanged montmorillonites, on kaolinite, and on silica gel was also examined in less detail; qualitatively, the conversion of trichloroethylene to dichloroacetic acid in a 48-h period occurred with the following order of decreasing efficiencies: Zn super(2+)-montmorillonite > silica gel > kaolinite > Ca super(2+)-montmorillonite > whole soil > Cu super(2+)-montmorillonite. These results show that the photoinduced decomposition of absorbed trichloroethylene occurs on a variety of adsorbents, generating products and intermediates that are similar to what have been reported previously for TiO sub(2)-based photodecomposition but with much longer time scales. These conversions can, therefore, be expected to occur in sunlight at the air-soil interface.
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