Physico-Chemical Properties of TiO2 Coatings Derived From Acid Catalyst-Free Precursor via Spin Coating

The present method of producing titania (TiO2) coatings involves the addition of an acid catalyst to prolong the shelf life of the initial precursor. However, this method has complex chemical routes that favor rutile TiO2 and result in higher bandgap energy. In this current work, unheated and heated TiO2 coatings were successfully prepared via spin-coating using an acid catalyst-free titania precursor. The TiO2 coatings were thoroughly investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman, Fourier transformed infrared (FTIR), and UV-Visible spectroscopic techniques. From XRD and Raman data, the unheated coating is amorphous, while the heated sample consists of anatase polymorph of TiO2. The FTIR results revealed traces of organic residues for the heated sample due to the organic nature of the precursor used. SEM showed that both samples were not uniform, porous, and consisted of spherical micro/nanostructured particles with some aggregation ascribed to the nature of the precursor. Diffuse reflectance indicated an absorption band edge at the UV region and showed similar absorption spectra to commercial TiO2 powder. However, a redshift of the UV-Vis reflectance spectra of the heated sample was observed. Using the baseline approach, the indirect optical bandgap of the unheated TiO2 coating decreased from 3.31 to 3.26 eV (+/- 0.2 eV) after the heat treatment, which is due to the crystallization of the sample into anatase TiO2.