Experimental and theoretical studies of Fe-doped TiO₂ films prepared by peroxo sol-gel method

Transparent, uniform, crack-free and visible light activated Fe-doped TiO₂ thin films have been prepared by an organic-free approach using titanium tetrachloride (TiCl₄), Fe³⁺ and ammonium hydroxide solutions to form yellow aqueous peroxo titanic acid (PTA) solution. Pure glass was made superhydrophilic after heating at 550 °C for 1 h and was used as the coating substrate. The PTA solution dispersed uniformly on the superhydrophilic glass by forming a thin film, resulting in a crack-free Fe-doped TiO₂ film as observed under FESEM. XRD results confirmed the presence of only anatase phase for all samples after calcination at 550 °C. The Fe-doped TiO₂ films exhibited slight red-shift in absorbance and enhanced absorbance in the visible-light region compared with undoped TiO ₂, attributed to bandgap narrowing by successful Fe³⁺ doping into TiO₂, which is supported by DOS calculations. Photodegradation of stearic acid (SA) revealed that Fe³⁺ doping increased visible light photocatalytic activity four-fold compared to undoped TiO₂ at optimal Fe-doped TiO₂ (1 wt% Fe³⁺) film. At higher Fe ions concentrations, the existence of increased charge recombination sites and segregated iron oxide phase suppressed the photoactivity.