Doping level effect on visible-light irradiation W-doped TiO2–anatase photocatalysts for Congo red photodegradation

A series of W-modified TiO2 (W–TiO2) photocatalysts were synthesized by a simple sol–gel method. The new photocatalysts were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis-diffuse reflectance spectroscopy (DRS), and Brunauer, Emmett and Teller (BET) surface area analyzer. The photoactivity of the W–TiO2 photocatalysts was evaluated by the photocatalytic oxidation of Congo red (CR) dye. It was found that the average size of the prepared photocatalysts is 10 nm. Moreover, they have high surface areas (∼ 216 m2 g−1) and their light-absorption extends to the visible region compared to pure TiO2. The effects of W-loading and of the calcination temperature of the prepared photocatalysts on their photocatalytic activity were also studied. The obtained results show that the W0.5–TiO2 photocatalyst calcined at 350 °C is much highly photoactive than non-doped or highly doped TiO2. The enhanced photocatalytic activity of the weakly doped TiO2 may be attributed to the increase in the charge separation efficiency and the presence of surface acidity on the W0.5–TiO2 photocatalyst.