Preparation and evaluation of composite with a natural red clay and TiO2 for dye discoloration assisted by visible light

Abstract A composite with a natural red clay (taua) and TiO2, labeled TiO2/Taua, was prepared and its photocatalytic activity assessed using methylene blue as model molecule. The photocatalytic activity for the individual components, taua and TiO2, was also evaluated under the same conditions. The natural clay was previously characterized by XRD and TGA that found the presence of hematite phase, a narrow band gap semiconductor (Eg = 2.1 eV), and low organic matter content. The X-ray diffraction analysis has shown also the presence of anatase, the most photoactive phase, in the composite as well as in the pure TiO2 prepared by sol-gel method. The results indicate that the TiO2/Taua composite has a higher photocatalytic activity than the individual components when irradiated with visible light in the presence of H2O2. The synergistic effect of the composite can be attributed to the highest adsorption capacity of dye and the heterojunction formation, TiO2/α-Fe2O3. The results have shown that the set of parameters providing the largest dye degradation rate was: initial dye concentration of 30 mg L− 1, H2O2 concentration of 1.7 mg L− 1 and power lamp fixed at 700 W. Under these conditions the methylene blue degradation was around 100% in 180 min.