Abstract

Recently the advantages of titanium dioxide (TiO2), as one of the most recognized photocatalysts for the degradation of organic compounds in wastewater, have prompted a great deal of research. However, its unsatisfactory efficiency caused by the large bandgap of TiO2 and high recombination rate of photo-generated e-/h+ has limited its application. Thermal spray processes as environmentally friendly technologies appear as a versatile and rapid processing approach compatible with industrial production. Suspension plasma spray (SPS) deposition could be used to obtain TiO2 deposits with an effective photoactive performance to decompose organic compounds and antiviral applications. Furthermore, TiO2 coatings with various degrees of sub-stoichiometric oxidation can be achieved with plasma spray deposition.
In this project, coatings with different anatase phase contents were produced. The results show no direct correlation between anatase content and the photocatalytic activity of as-sprayed coatings due to their unique microstructure and the presence of oxygen vacancies. In comparison, anatase phase positively enhanced the photocatalytic activity in the post-treated coatings with similar coating characteristics and oxygen contents.
Moreover, oxygen vacancy presented an influential role in improving the photocatalytic activity of sub-stoichiometric TiO2-x coatings produced by SPS. The energy levels introduced by oxygen vacancies and Ti3+ ions in TiO2 lattice sites decreased the bandgap energy and shifted the absorption edge to visible light. The energy levels can also improve the charge carriers’ lifetime by acting as traps for electrons and holes. Results showed that the photocatalytic activity of as-sprayed sub-stoichiometric TiO2-x coatings was 2-3 times higher than that of post-treated stoichiometric TiO2 coatings.
Further studies on the cerium-doped TiO2 showed SPS-SPPS technique as a promising method for doping TiO2. However, results revealed the importance of adding an optimum amount of dopant to reach the highest photoactivity. Moreover, a nanocomposite of TiO2- CeO2 can help photocatalytic activity. Otherwise, sub-micron CeO2 particles in the composite matrix could cover the active surface of TiO2 particles and decrease the photocatalytic efficiency.
Finally, the antiviral performance of the coatings was assessed. The results show that thermally sprayed coatings can introduce a potentially cost-effective solution to produce efficient antiviral high-touch coatings for indoor/ outdoor applications.