A Visible Light-Driven Titanium Dioxide Photocatalyst Codoped with Lanthanum and Iodine: An Application in the Degradation of Oxalic Acid

A series of photocatalysts was synthesized by codoping TiO 2 with lanthanum and iodine (La−I−TiO 2 ). The structure and properties of the catalysts were studied by X-ray diffraction (XRD), the Brunauer−Emmett−Teller (BET) method, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV−vis diffuse reflectance spectra. The prepared anatase-phase La−I−TiO 2 (molar ratio 20:20:100) calcined at 400 °C had a BET surface area of 92.9 m 2 g −1, and the crystallite size calculated from XRD data was ∼3.57 nm, and it had a remarkable absorption in the visible light range of 400−550 nm. The catalytic efficiency was tested by monitoring the photocatalytic degradation of oxalic acid under visible light irradiation. An optimum molar ratio of 20:100 La/TiO 2 was determined for the most efficient inhibition of the recombination of electron−hole pairs and the photocatalytic activity of La−I−TiO 2 calcined at 400 °C was significantly higher than that calcined at 500 or 600 °C in aqueous oxalic acid solution. The probable process of oxalic acid degradation was that it was first adsorbed onto the surface of the catalysts, where it reacted with valence band holes ( h vb + ) and the surface-bound or adsorbed • OH radicals ( • OH ads ) as well as reactive oxygen species (ROS) derived from oxygen reduction by photogenerated electrons, and finally converted into CO 2 and H 2 O without any stable intermediate.