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.