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 TiO2 with lanthanum and iodine (La-I-TiO2). 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-TiO2 (molar ratio 20:20:100) calcined at 400 degrees C had a BET surface area of 92.9 m(2) g(-1), and the crystallite size calculated from XRD data was similar to 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/TiO2 was determined for the most efficient inhibition of the recombination of electron-hole pairs and the photocatalytic activity of La-I-TiO2 calcined at 400 degrees C was significantly higher than that calcined at 500 or 600 degrees 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)-O-center dot radicals ((OHads)-O-center dot) as well as reactive oxygen species (ROS) derived from oxygen reduction by photogenerated electrons, and finally converted into CO2 and H2O without any stable intermediate.