Band gap and morphology engineering of TiO2 by silica and fluorine co-doping for efficient ultraviolet and visible photocatalysis

Abstract

Silicon and fluorine co-doped anatase TiO₂ (Si–F–TiO₂) photocatalysts with enhanced photocatalytic activity were successfully prepared via a facile two-step synthetic method by using SiO₂ powders and (NH₄)₂TiF₆ as the precursors. The obtained products were thoroughly characterized using various techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-visible diffuse reflectance spectroscopy and N₂ adsorption–desorption analysis. The characterization revealed the effects of molar ratio of silica to titanium (R) and pH value on morphology, size and crystal structure of Si–F–TiO₂ samples. We find that the band gap of the catalyst can be engineered from 3.16 to 2.88 eV via altering the molar ratio of Si : Ti and the pH value. Compared with un-doped or F-doped TiO₂, co-doped Si–F–TiO₂ samples exhibited improved photocatalytic degradation toward different dye molecules under both ultraviolet and visible light illumination. With the aid of hole and radical trapping experiments, we proposed a photocatalytic mechanism for the examined systems. Furthermore, first-principle calculations provide theoretical insights for the enhanced photocatalytic performance of codoped Si–F–TiO₂ photocatalyst.