Thickness dependent activity of nanostructured TiO2/α-Fe2O3 photocatalyst thin films

The effect of thickness of TiO2 coating on synergistic photocatalytic activity of TiO2 (anatase)/α-Fe2O3/glass thin films as photocatalysts for degradation of Escherichia coli bacteria in a low-concentration H2O2 solution and under visible light irradiation was investigated. Nanograined α-Fe2O3 films with optical band-gap of 2.06 eV were fabricated by post-annealing of thermal evaporated iron oxide thin films at 400 °C in air. Increase in thickness of the Fe2O3 thin film (here, up to 200 nm) resulted in a slight reduction of the optical band-gap energy and an increase in the photoinactivation of the bacteria. Sol–gel TiO2 coatings were deposited on the α-Fe2O3 (200 nm)/glass films, and then, they were annealed at 400 °C in air for crystallization of the TiO2 and formation of TiO2/Fe2O3 heterojunction. For the TiO2 coatings with thicknesses ≤50 nm, the antibacterial activity of the TiO2/α-Fe2O3 (200 nm) was found to be better than the activity of the bare α-Fe2O3 film. The optimum thickness of the TiO2 coating was found to be 10 nm, resulting in about 70 and 250% improvement in visible light photo-induced antibacterial activity of the TiO2/α-Fe2O3 thin film as compared to the corresponding activity of the bare α-Fe2O3 and TiO2 thin films, respectively. The improvement in the photoinactivation of bacteria on surface of TiO2/α-Fe2O3 was assigned to formation of Ti–O–Fe bond at the interface.