Sulfur-doped highly ordered TiO2 nanotubular arrays with visible light response

The future of TiO2-based photocatalysts strongly depends on their structural optimization so as to obtain high activity as well as visible light responses Recently we successfully fabricated sulfur-doped highly ordered TiO2 nanotubular arrays by potentiostatic anodization of titanium foils, followed by annealing in a flow of H2S at 380 degrees C. The as-prepared arrays were characterized using field emission scanning electron microscopy, differential scanning calorimetry, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS), and photoelectrochemical measurements. The results clearly show that the vertically oriented nanotubular arrays are highly ordered with a wall thickness of 10 nm. After being annealed at 380 degrees C, the original TiO2 nanotubular arrays were transformed from an amorphous structure to an anatase phase with a crystallization enthalpy of 324.6 J/g. With treatment in a H2S atmosphere, sulfur ions were incorporated into oxygen atom sites in the TiO2 nanotubes to form O-Ti-S bonds, confirmed by high-resolution XPS of S2p and Ti2p and XRD analysis. The sulfur doping caused the absorption edge of TiO2 to shift into the lower energy region, making the nanotubular arrays active under visible light irradiation up to 650 nm, demonstrated by UV-vis DRS and photocurrent measurements.