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In this research, pure SnO 2 was deposited on 316 stainless steel plates using air plasma spraying. Micrograph and phase composition of the deposited films were studied using SEM and X-ray diffraction, respectively; and methylene blue solution was used to evaluate the activity of the deposited photocatalytic coatings. It was shown that air plasma spraying could be used as an efficient method to deposit pure SnO 2 photocatalytic coatings. UV-vis diffuse reflectance spectra analysis showed higher photo-absorption ability of the deposited films as compared to the initial powder. Although all the tin oxide coatings had lower band gap energy than the initial powder, further studies are needed to deposit SnO 2 films, which can act as photocatalytic coatings under visible light irradiation. Comparison of the photocatalytic activity of tin oxide coatings with that of ZnO film showed the adequate activity of tin oxide coatings deposited by air plasma spraying.

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Water pollution is considered a serious threat to human life. An advanced oxidation process in the presence of semiconductor photocatalysts is a popular method for the effective decomposition of organic pollutants from wastewater. TiO2 nanoparticles are widely used as photocatalysts due to their low cost, chemical stability, environmental compatibility and significant efficiency. The aim of this study is to review the photocatalytic processes and their mechanism, reaction kinetics, optical and electrical properties of semiconductors and unique characteristics of titanium as the most widely used photocatalyst; and to compare the photocatalytic activity between different titania phases (anatase, rutile, and brookite) and between colorful and white TiO2 nanoparticles. Photocatalytic processes are based on the creation of electron–hole pairs. Therefore, increasing stability and separation of charge carriers could improve the photocatalytic activity. The synthesis method has a significant effect on the intensity of photocatalytic activity. The increase in the density of surface hydroxyls as well as the significant mobility of the electron–hole pairs in the anatase phase increases its photocatalytic activity compared to other phases. Electronic and structural changes lead to the synthesis of colored titania with different photocatalytic properties. Among colored titania materials, black TiO2 showed promising photocatalytic activity due to the formation of surface defects including oxygen vacancies, increasing the interaction with the light irradiation and the lifetime of photogenerated electron–hole pairs. Among non-metal elements, nitrogen doping could be effectively used to drive visible light-activated TiO2.

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