Study of the incorporation of S in TiO2/SO42− Coatings produced by PEO process through XPS and DFT

TiO2 has been widely studied due to its wide range of applications. Various techniques have been used for its synthesis. Plasma Electrolytic Oxidation (PEO) has been a synthesis technique of great interest since it allows obtaining coatings and incorporating different ions at environmental conditions. In this work, the synthesis of TiO2/SO42− was carried out by means of PEO, characterized by Raman, XRD (X-Ray Diffraction) and XPS (X-Ray Photoelectrons Spectroscopy). The experimental results were used for DFT (Density Functional Theory) simulations. For the PEO process, 99% Ti sheets, 0.10 M H2SO4 and 6 min synthesis time were used with useful cycle variations of 2% and 50%. On the other hand, DFT calculations were carried out to demonstrate the formation of structural defects in TiO2/S systems from the experimental results. The Raman and the XRD results show the presence of anatase and rutile phase of TiO2 in both useful cycles. The XPS results showed the presence of S in the form of SO42−, both on the surface of the material and in the bulk. The calculations showed that the quantification of sulfate ions in the Ti site was energetically favorable with a formation energy value of −3.09 eV, slightly lower than that of the bulk without substitution, which was −3.21 eV. Additionally, the DOS (densities of state) and substitution energy were analyzed.