Optical and photocatalytic properties of Fe3+-doped TiO2 thin films prepared by a sol–gel spin coating

Various iron ion (Fe3+) doped titanium dioxide (TiO2) thin films (Fe3+-doped TiO2) have been successfully prepared on a glass substrate by a sol–gel spin coating route using titanium tetraisopropoxide and iron(III) nitrate nonahydrate as the initial materials. After the Fe3+-doped TiO2 thin films were calcined at 823 K for 1 h, the effect of Fe3+-doping on the optical properties and photocatalytic activity were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), ultraviolet– visible spectroscopy, spectroscopic ellipsometry and photocatalytic degradation of methylene blue. The XRD results showed that all Fe3+-doped TiO2 thin films contained only a single crystalline phase of anatase TiO2 after calcining at 823 K for 1 h. Moreover, the XRD results also revealed that the crystallinity and crystalline size decreased with increased Fe3+-doping due to worsening of the crystallization of anatase TiO2. FESEM micrographs showed that all Fe3+-doped TiO2 thin films have smooth surfaces containing granular nanocrystallines and are without cracks. The UV–vis absorption spectra showed that the absorption of the TiO2 thin films had a small red-shift as the Fe3+-doping increased. The direct band gap energy (Egd) and indirect band gap energy (Egind) of Fe3+-doped TiO2 films decreased with increasing Fe3+-doping. Moreover, the rate constant of methlylene blue decomposition increased from 0.018 to 0.038/h as the Fe3+-doped content increased from 0 to 25 wt%.