Under UV light irradiation at a wavelength longer than 320 nm, TiO₂ could catalyze selective oxidation of hexane by O₂ into hexanone and hexanol intermediates. It was found that addition of a small amount of NaF into the aqueous suspension could result in significant enhancement in the photocatalytic activity of anatase-type TiO₂. As fluoride concentration was increased, the amount of hexanone and hexanol, and the molar ratio of hexanol to hexanone, were all increased toward saturation, while the initial pH (3.0 and 5.5) had little effect. As the sintering temperature of TiO₂ was increased, the amounts of hexanone and hexanol formed were first increased and then decreased. In the presence of NaF, a similar sintering temperature effect was exhibited, but the trend in the increased amounts of hexanone and hexanol was not in agreement with the changes in the amount of fluoride adsorbed on TiO₂. Moreover, the photocatalytic activity of rutile-type TiO₂ was low, and in the presence of NaF, the production of hexanone and hexanol was partially inhibited. The influencing factors are discussed. The hypothesis is presented again that fluoride hydrogen bonding formed in the double layers of TiO₂ can promote desorption of surface bound hydroxyl radical, thus accelerating hexane oxidation and improving the yields of hexanone and hexanol production.

Key words: cyclohexane, cyclohexanone, cyclohexanol, titanium dioxide, photocatalysis, fluoride