Chemical adsorption of phosgene on TiO2 and its effect on the photocatalytic oxidation of trichloroethylene

We observed the chemical adsorption with gas-phase phosgene on TiO2 surfaces using in situ FT-IR, and examined its effect on the photocatalytic decomposition of trichloroethylene (TCE). The infrared spectrum of the adsorbed standard phosgene suggested that phosgene reacts with surface hydroxyl groups to form a bidentate carbonate compound, which binds to the TiO2 surface through two Ti–O bonds. The surface species, adsorbed phosgene, derived from dichloroacetyl chloride (DCAC), which is generated during the photocatalytic decomposition of TCE, was also found to yield the same bidentate carbonate when decomposed photocatalytically. The adsorbed phosgene was formed stably on TiO2 and was found to play an important role in accelerating the decomposition of TCE under irradiation with visible light as well as with UV. The active species was considered to be active oxygen on the structure of phosgene stably adsorbed to bidentate carbonate. The surface structure of adsorbed phosgene, bidentate carbonate may be used for the surface improvement of photocatalysts under visible light as well as UV.