Visible-light-driven N–F-codoped TiO 2 powders derived from different ammonium oxofluorotitanate precursors

Abstract

We report on the synthesis of N–F-codoped TiO 2 powders with a homogenous anatase structure via a thermal decomposition of the ammonium oxofluorotitanate ((NH 4) 0.3TiO 1.1F 2.1, NH 4TiOF 3 and (NH 4) 2TiOF 4) precursors at 550 °C for 1 h in air. The ammonium oxofluorotitanate precursors were synthesized by a wet chemical method in the mixture of deionized water and absolute ethanol using titanium tetrachloride (TiCl 4) and ammonium fluoride (NH 4F) as reactants. The as-prepared samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetry–differential scanning calorimetry (TG–DSC), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and UV–vis spectroscopy. The results from XRD, TG–DSC and FTIR analyses confirmed a complete thermal conversion of the ammonium oxofluorotitanate precursors to N–F-codoped anatase TiO 2 at a temperature of > 500 °C. The SEM and TEM observations exhibited that the morphologies of the precursors were not considerably affected by the thermal treatment at 550 °C for 1 h. The XPS data proved the presence of the nitrogen and fluorine atoms in the TiO 2 structure. According to the resulting UV–vis spectra, the as-prepared samples demonstrated a strong visible-light absorbance in the wavelength range of 400–550 nm. The photocatalytic activity of the N–F-codoped anatase TiO 2 was evaluated through a study of the decomposition of methyl orange under visible light irradiation. It was found that the sample derived from the (NH 4) 0.3TiO 1.1F 2.1 precursor by thermal treatment at 550 °C for 1 h showed much higher photocatalytic activity compared to the commercial undoped TiO 2 (Degussa P25) due to the synergetic effects of a strong absorption in the visible-light region, red shift in absorption edge, good crystallinity, and porous structure.