Enhancement of Photocatalytic Activity of Mesporous TiO₂ Powders by Hydrothermal Surface Fluorination Treatment

Mesporous surface-fluorinated TiO 2 (F−TiO 2 ) powders of anatase phase with high photocatalytic activity are prepared by a one-step hydrothermal strategy in a NH 4 HF 2 −H 2 O−C 2 H 5 OH mixed solution with tetrabutylorthotitanate (Ti(OC 4 H 9 ) 4, TBOT) as precursor. The prepared samples are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, N 2 adsorption−desorption isotherms, UV−vis absorption spectroscopy, and transmission electron microscopy. The production of hydroxyl radicals ( • OH) on the surface of UV-illuminated TiO 2 is detected by a photoluminescence (PL) technique with use of terephthalic acid as a probe molecule. The photocatalytic activity is evaluated by photocatalytic oxidation decomposition of acetone in air under UV light illumination. The results show that the photocatalytic activity of F−TiO 2 powders is obviously higher than that of pure TiO 2 and commercial Degussa P25 (P25) powders due to the fact that the strong electron-withdrawing ability of the surface ≡Ti−F groups reduces the recombination of photogenerated electrons and holes, and enhances the formation of free OH radicals. Especially, the F−TiO 2 powder prepared at the nominal atomic ratio of fluorine to titanium ( R F ) of 0.5 shows the highest photocatalytic activity and its rate constant k exceeds that of P25 by a factor of more than 3 times.