Phase Composition, Microstructure, and Optical Characteristics of Spin-Coated La-TiO2 and Fe-TiO2

Herein, TiO2, La-added, and Fe-added TiO2 coatings are synthesized by sol-gel spin coating using acid catalyst-free titania precursors, and their microstructural and optical characteristics are studied. The possible reaction mechanism for synthesizing TiO2-based coatings using catalyst-free precursor is presented and correlated to their microstructural characteristic. TiO2 coatings are developed and found to be anatase in phases having submicron morphological features. The anatase composition of TiO2 coating decreases with increasing La or Fe ion concentrations. This manifests the inhibitory effect of increasing La and Fe ions to the formation of anatase TiO2. Moreover, the addition of La ions caused no significant changes in the reflectance spectra and bandgap energy of TiO2. In contrast, a remarkable red shift was observed with increasing Fe ion concentration. The calculated bandgap decreases from 3.261 to 2.096 eV with the addition of 7.5 mol% Fe ions, attributed to the formation of new energy states below the conduction band of TiO2 induced by the Fe ion. These results suggested that a low-cost Fe added-TiO2 material can be synthesized using an acid catalyst-free precursor that could extend the photocatalytic efficiency of TiO2 to the visible light region.