Effects of Lithium Doping in TiO<sub>2</sub> Thin Films on Their Structural, Optical, and Morphological Properties, and on the Degradation Efficiency of Methylene Blue Dye

In this study, we investigate the impact of lithium (Li+) doping on the structural, morphological, optical, and photocatalytic properties of TiO2 thin films. Li+-doped TiO2 films were fabricated on glass substrates using the sol–gel spin-coating technique and subsequently annealed at 550°C for 2 h. X-ray diffraction analysis confirmed that all films crystallize exclusively in the anatase phase. The crystallite size was found to decrease from 19 to 13 nm with increasing Li+ doping. The surface morphology, examined through scanning electron microscopy and atomic force microscopy, revealed noticeable changes influenced by the Li+ content. With higher Li+ concentrations, optical transmittance (T [%]) increased, while the optical band gap (Eg [eV]) decreased. Additionally, lithium doping enhanced the photocatalytic efficiency of TiO2 films in degrading methylene blue.