One-step hydrothermal fabrication and photocatalytic activity of surface-fluorinated TiO2 hollow microspheres and tabular anatase single micro-crystals with high-energy facets

Surface-fluorinated TiO2 hollow microspheres and tabular-shaped anatase single micro-crystals with highly energetic (001) facets exposed were prepared by a one-step hydrothermal strategy using ammonium bifluoride (NH4HF2) as a morphology controlling agent. The prepared samples were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and N-2 adsorption-desorption isotherms. Production of (OH)-O-center dot radicals on the TiO2 surface was detected by a photoluminescence (PL) technique using terephthalic acid as a probe molecule. The photocatalytic activity of the as-prepared samples was evaluated by photocatalytic decolorization of Rhodamine B (RhB) aqueous solution at ambient temperature. The results indicate that the particle morphology, average crystallite size, specific surface areas, pore structures, and photocatalytic activity of the TiO2 samples can be readily controlled by changing the concentration of NH4HF2. With increasing NH4HF2 concentration, the average crystallite size and average pore size increase, whilst the specific surface area, pore volume and porosity steadily decrease. The photocatalytic activity of the as-prepared samples exceeds that of Degussa P25 (P25) when the molar ratios of fluorine to titanium (R-F) are kept in the range of 0 to 1.