Effect of Both Sn Doping and Annealing Temperature on the Properties of Dip-Coated Nanostructured TiO2 Thin Films

The synthesis of active thin films supported on substrates overcomes the drawbacks of powder-based photocatalysis and energy harvesting. In this study, semiconducting thin films of pristine TiO2 and Sn doped TiO2 were coated on glass substrates by the sol–gel dip-coating method. The effect of both annealing temperature (450 and 500 °C, during 2 h in air atmosphere) and Sn dopant content (1, 3 and 5 at.%) on the structural, morphological and optical properties of Sn doped TiO2 films were studied. The correlation between these properties and the photocatalytic performance of the films in the removal of Rhodamine B solution under UV light was investigated. At 450 °C, Sn:TiO2 films exhibit anatase–brookite mixed phase, while at 500 °C, the films exhibit anatase phase. The crystallites sizes of the films were on a nanometer scale, between 19.01 and 26.57 nm. The pristine TiO2 film treated at 450 °C has a compact morphology with spherical grains, and after adding different Sn content, the nano-spheres turn into nanorods. At 500 °C, all the films illustrate a porous morphology with spherical grains. The two series are transparent in the visible region and have an optical band gap of 3.23–3.54 eV. The (e−/h+) recombination rate of TiO2 film decreases as a function of Sn doping. The latter enhances the photocatalytic efficiency of porous TiO2 film and 1 at.% Sn:TiO2 exhibits the highest degradation rate, which can be attributed to a larger surface area and less (e−/h+) recombination rate.