Dependence of photocatalytic activity on the compositions and photo-absorption of functional TiO2–Fe3O4 coatings deposited by plasma spray

Owing to the much concern with global environmental issues, Fe3O4 added photocatalytic TiO2 coatings were deposited using plasma spray for environmental depollution. The influence of the content of Fe3O4 additive to the TiO2 powder on the phase composition, microstructure and photo-absorption of plasma-sprayed TiO2 coatings was systematically studied. The results showed that the TiO2–Fe3O4 coatings consisted of anatase TiO2, rutile TiO2 and Fe2TiO5 pseudobrookite phase which appeared when the content of Fe3O4 additive was equal to or over 10%. The content of FeTiO3 was highest in the sprayed TiO2–10%Fe3O4 coatings. The addition of Fe3O4 improved the anatase–rutile transformation of TiO2–Fe3O4 powders. Furthermore, it was found that TiO2 coatings can decompose acetaldehyde under the illumination of ultraviolet rays, and the degrading efficiency was improved with an increase of FeTiO3 content in the coatings. A two-step electron transfer model was proposed to explain the good photocatalytic activity of the sprayed coating with high content of FeTiO3. However, presence of large amount of Fe2TiO5 compound substantially reduced the photocatalytic efficiency of the sprayed TiO2–Fe3O4 coatings for its unfavorable photo-excited electron–hole transfer process.