Elaboration and characterization of undoped and doped titanium dioxide thin layers by sol gel (spin coating) for photocatalytic applications

Abstract

Titanium dioxide thin films were deposited by sol-gel spin coating technique using titanium tetra-isopropoxide, absolute ethanol and acetylacetone as precursor solution, solvent and catalyzer, respectively. The effect of the solution concentration, rotation speed, molar ratio and gallium doping concentration on the structural, morphological, optical and photocatalytic properties of TiO2 thin films was studied. All films were characterized by multiple techniques such as X-ray diffraction (XRD), UV-Visible spectroscopy, scanning electron microscope (SEM), photoluminescence (PL) spectroscopy and Fourier transform infrared (FTIR) spectroscopy to investigate the physical properties of titanium dioxide films. X-ray diffraction analysis shows that all films are oriented preferentially along to (101) plane. SEM images show that the films are homogenous, uniform and dense with some holes and cracks. The optical transparency of TiO2 films around to 90% in visible range which related to good crystalline state of the films. The direct band gap was varied between 2.99 and 3.6 eV. The photoluminescence analysis revealed mainly three emission peaks (ultraviolet, blue and green) corresponding to the near band edge (NBE) and defect levels (DL) emissions. It found at 0.2 M, the samples have a photocatalytic property with the photodegradation rate reach to 84%. The latter is improved used galuim doping TiO2 which became equal to 95%. Whereas, the photodegradation rate reaches to 94 % at t = 180 min in undoped TiO2 films with molar ratio y = 0.66. The elaborated films (deposited at 4000 rpm) as a photocatalyst to change the water acidity from pH = 4.8 to pH = 7.4 with produce H2 gas. The latter used as a promising fuel for the future that protects the environment from pollution.