Influence of fluorine on the structure and photocatalytic activity of TiO2 film prepared in tungstate-electrolyte via micro-arc oxidation

TiO2 films were prepared on pure titanium substrate via micro-arc oxidation (MAO) technique in tungstate-electrolyte. The influence of fluorine ion concentration in electrolyte on the microstructure and photocatalytic activity of TiO2 films was investigated. The results showed that the porosity, element content and phase composition of TiO2 films were affected by fluorine ion concentration in electrolyte. The number of pores, the content of tungsten and the content of anatase phase all increased when appropriate fluorine ion was added into the electrolyte. Thus, the photocatalytic activity of TiO2 films could be promoted by adding appropriate fluorine ion into the electrolyte. The addition of fluorine ion did not alter the iso-electric points of TiO2 films. It was confirmed by UV–Vis spectrophotometer that the photocatalytic activity of the film prepared in electrolyte containing 2 g/L NaF was higher than that of the films prepared in other electrolytes during the degradation of methyl orange.