Role of lanthanum species in improving the photocatalytic activity of titanium dioxide

Abstract

Series of lanthanum-modified TiO₂ catalysts were prepared by a UV photodeposition method to exclude any heat treatments that may affect the properties and photocatalytic activity of TiO₂. Results showed that the lanthanum modification did not significantly affect the properties of TiO₂, but increased the formation of Ti³⁺. Under UV light irradiation, the activity for 2,4-D decomposition rose by a maximum factor of 5.5 when TiO₂ was loaded with 5 mol% La; further increase of La deposition led to a decrease in photocatalytic activity. From the electrochemical impedance and photocurrent results, it was shown that the positive influence of La on TiO₂ photocatalytic activity was caused by the increased charge separation in the TiO₂ photocatalysts, owing to the additional formation of Ti³⁺ states. On the other hand, when tested with the colourless 2,4-D model pollutant under visible and solar simulator irradiation, the presence of lanthanum species did not improve the photocatalytic activity of TiO₂ significantly. Hence, it was shown that lanthanum species only improved the UV photocatalytic activity of TiO₂.