Optical and photocatalytic properties of Fe~(3+)-doped TiO_2 thin films prepared by a sol-gel spin coating

摘要

Various iron ion (Fe~(3+)) doped titanium dioxide (TiO_2) thin films (Fe~(3+)-doped TiO_2) 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 Fe~(3+)-doped TiO_2 thin films were calcined at 823 K for 1 h, the effect of Fe~(3+)-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 Fe~(3+)-doped TiO_2 thin films contained only a single crystalline phase of anatase TiO_2 after calcining at 823 K for 1 h. Moreover, the XRD results also revealed that the crystallinity and crystalline size decreased with increased Fe~(3+)-doping due to worsening of the crystallization of anatase TiO_2. FESEM micrographs showed that all Fe~(3+)-doped TiO_2 thin films have smooth surfaces containing granular nanocrystallines and are without cracks. The UV-vis absorption spectra showed that the absorption of the TiO_2 thin films had a small red-shift as the Fe~(3+)-doping increased. The direct band gap energy (E_g~d) and indirect band gap energy (E_g~(ind)) of Fe~(3+)-doped TiO_2 films decreased with increasing Fe~(3+)-doping. Moreover, the rate constant of methlylene blue decomposition increased from 0.018 to 0.038/h as the Fe~(3+)-doped content increased from 0 to 25 wt%.