Comparative study of the structural, optical and photocatalytic properties of semiconductor metal oxides toward degradation of methylene blue

Indium oxide (In2O3), zinc oxide (ZnO), stannic oxide (SnO2), and titanium dioxide (TiO2) thin films were prepared on glass substrates using electron beam evaporation. The samples characterized by UV–vis spectroscopy, diffraction ray-X and scanning electron microscopy techniques. The photocatalytic degradation of methylene blue in an aqueous solution, as a model compound, was investigated using different metal oxides in an attempt to compare the decomposition reaction rate. The progress of degradation was monitored using UV–vis spectrophotometry. The effects of various experimental parameters such as initial concentration of methylene blue (5–10 mg/l), pH of the solution (2–8), annealing temperature (250–550 °C), and catalyst nature and its microstructure were systematically studied in order to achieve maximum degradation efficiency. The results obtained were fitted with the Langmuir–Hinshelwood model to study the degradation kinetics and discussed in detail. Nearly complete degradation was obtained at optimal operational parameters including the higher annealing temperature of thin film and the increase in MB solution pH. The degradation with In2O3 was more efficient than with SnO2, ZnO and TiO2 films.