Microstructure and photocatalytic properties of WO3/TiO2 composite films by plasma electrolytic oxidation

WO3/TiO2 composite films were prepared by plasma electrolytic oxidation in electrolytes containing different tungstate concentration. The morphology, topography, compositions, crystal structure and photophysical properties of films were characterized by SEM, AFM, EDX, XRD, XPS, UV–vis DRS and PL, the surface acidity of films was investigated by ATR-IR. The results showed porous films formed on the titanium substrate, consisted of Ti, O and W, and presented mixed crystal of anatase and rutile. Tungsten species were well-dispersed for WO3/TiO2 film formed in lower tungstate concentration, but were in crystalline WO3 in higher concentration. For WO3/TiO2 film prepared in optimal tungstate concentration, the highest content of anatase and the maximum surface acidity were obtained, and the recombination of holes and electrons was effectively inhibited. However, coupled-WO3 did not shift the optical absorption to the visible region. The improvement of photocatalytic activity was attributed to the increased surface acidity, better separation between photo-induced carriers and higher content of anatase.