Photodegradation of azo dye Congo Red from aqueous solution by the WO3–TiO2/activated carbon (AC) photocatalyst under the UV irradiation

The WO3–TiO2/AC (activated carbon) photocatalyst used in the experiment was prepared by the sol–gel-dipping-calcination method. The photocatalyst was characterized by XRD and the photoactivity of it was tested by the degradation of azo dye Congo Red. In order to obtain the optimum preparation conditions of the photocatalyst and the optimum degradation conditions of Congo Red, two orthogonal tests have been applied. The results showed that the optimal preparation conditions of the photocatalyst were: calcination temperature 500 °C, the content of WO3 3% and the hours of calcination 3 h and the optimal conditions of Congo Red degradation were: the dosage of catalyst 10 g L−1, pH 7 and the amount of H2O2 114 mM. The effect of several co-existing negative ions on the photodegradation of Congo Red was investigated. It was found that ClO2−, BrO3− and S2O82− had a positive effect on the photodegradation of Congo Red in the following order: S2O82− > ClO2− > BrO3−. On the contrary, the anions such as SO42−, NO3−, Cl−, SO32−, H2PO4− decreased the photodecolorization percent of Congo Red. Their inhibitory effect were in the order SO32− > Cl− > H2PO4− > SO42− > NO3−. Finally, the kinetics process was studied and the photodegradation rate of Congo Red was found to obey pseudo-first-order kinetics equation represented by the Langmuir–Hinshelwood model.