Synthesis, characterization and visible light photocatalytic activity of Sn:TiO2/Si(100) thin films: impact of Sn doping and annealing temperature

In this research work the impact of Sn doping and different annealing temperature on the structural, morphological, optical and photocatalytic properties of titanium dioxide (TiO₂) and Sn doped TiO₂ thin films (TFs) were studied. The pristine TiO₂ and Sn doped TiO₂ TFs were prepared over dip-coated Si(100) substrate using sol–gel method. The XRD and Raman analysis results revealed that all TiO₂/Si(100) TFs crystallize into both anatase and rutile phases, and increasing the temperature accelerates the anatase–rutile phase transition. While, the addition of 1 at.% Sn leads to a complete transition from anatase to rutile phase at 800 °C. At the same time, the crystallites size of TiO₂ increased with the annealing temperature. However, reverse behavior is observed after doping TiO₂ with 1 at.% Sn. The morphological analysis done using AFM and SEM micrographs showed that, 1 at.% Sn dopant led to the formation of pores in the TiO₂/Si(100) TFs. Based on the reflectance results, 1 at.% Sn dopant shifted the absorption band of TiO₂/Si(100) TF from UV to visible region, and consequently reduced its band gap energy. The photocatalytic degradation of RhB under visible light proved that all 1 at.% Sn:TiO₂/Si(100) TFs were activated, and the film annealed at 600 °C has more enhanced activity (D% = 52%, K = 2.5 × 10^–3 min⁻¹), compared to other temperatures. This is attributed to the synergistic effect between anatase and rutile phases leading to better (e⁻/h⁺) pair’s separation.