Role of calcination in sol-gel synthesis of 5%In-0.05%Sm-TiO2 for photocatalytic degradation of methyl orange

Sol-gel method was used to prepare a novel 5% In-0.05% Sm-TiO2 photocatalyst. The materials were characterized by XRD, SEM, FT-IR/FIR, UV-Vis diffuse reflectance, and N-2 adsorption-desorption analyses. Anatase phase TiO2 is formed in all the samples while calcination temperature ranges from 350 degrees C to 600 degrees C. Cell volume of anatase TiO2 slightly expands with rising calcination temperature. The band gap energies of the 5% In-0.05% Sm-TiO2 samples calcined at 350 degrees C, 400 degrees C, 450 degrees C, 500 degrees C and 600 degrees C are 2.84, 2.90, 2.91, 2.95 and 3.02 eV, respectively. Specific surface area of the samples gradually decreases with rising calcination temperature, while the average pore size and total pore volume constantly increase at the same time. The maximum photocatalytic activity is found on the sample calcined at 400 degrees C. 97.7% of the initial methyl orange is removed from the solution after 45 min of irradiation. The conjugated chromophores in methyl orange molecule are almost decomposed at this time.