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

Mesporous surface-fluorinated TiO2 (F-TiO2) Powders of anatase phase with high photocatalytic activity are prepared by a one-step hydrothermal strategy in a NH4HF2-H2O-C2H5OH mixed solution with tetrabutylorthotitanate (Ti(OC4H9)(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)-O-center dot) on the surface of UV-illuminated TiO2 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-TiO2 powders is obviously higher than that of pure TiO2 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-TiO2 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.