Structural and optical properties of nitrogen-iron co-doped titanium dioxide films prepared via sol-gel dip-coating: Effect of urea and iron nitrate concentration in the sol

In this study, nitrogen-iron co-doped titanium dioxide films were prepared via sol-gel dip-coating method using urea and iron nitrate as nitrogen and iron source, respectively. Nonmetal doping of TiO₂ have some disadvantages such as massive charge carrier recombination and losing the photo-catalytic capability. Three different nitrogen-iron co-doped titanium dioxide sols with different urea and iron nitrate concentration were prepared. The resulting sols were homogeneous and transparent, and no precipitation was observed in any of them. It was observed that the film prepared with middle urea-iron nitrate concentration sol got opaque in a short time after the dip-coating process. All prepared films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, confocal microscopy and ultraviolet–visible (UV-Vis) spectroscopy. It was found that the concentration of the urea and iron nitrate in the sol had an effect on the crystal structure, microstructure, surface morphology and optical properties of the resulting films. Samples with middle concentrations had amorphous structure and bigger particle size. It was seen that sample with higher iron amount has lower band-gap. It is concluded that we can prepare transparent anatase, transparent amorphous and opaque amorphous titanium dioxide films by changing the urea and iron nitrate concentration in the sol.