Surface Modification of TiO₂ Using Chlorofluoromethane or Hydrofluoromethane

Abstract

Fine powder of TiO₂ was treated with various chlorofluoromethanes or CHF₃ in an ordinary flow reactor under an atomospheric pressure for the surface modification of the powder. The results revealed that surface fluorination readily proceeded at temperatures higher than 250°C, especially at above 350°C. Chlorine component was little introduced into the surface except for the treatment using CCl₃F. The effect of the treatment on the surface acidity was highly dependent on the pretreatment temperature. Thus, the surface acidity of TiO₂ heat-treated at 600°C was fairly enhanced by the chlorofluoromethane-treatment ; on the other hand, that of TiO₂ heat-treated at a much higher temperature, 900°C, was decreased by the treatment because surface fluorination took place instead. Adsorptions of hexane and water vapor showed that the treated TiO₂ surfaces turned out to be more hydro- and lipo-phobic with the treatment. In addition, a test for the photo-catalytic activity of TiO₂, displayed that the TiO₂ surface was made to be more stable to UV light by the chlorofluoromethane-treatment.