Photocatalytic removal of 2,4-d herbicide on lanthanum oxide-modified titanium dioxide

Titanium dioxide (TiO2) has been recognized as an active photocatalyst for degradation of various organic pollutants. In this study, in order to improve the photocatalytic activity of TiO2, the effect of lanthanum oxide modification was investigated by using commercial P25 as the benchmark. Lanthanum oxide/P25 TiO2 composites with 0.1, 0.5, 1 and 5 mol% of La loadings were prepared via an impregnation method. The resultant composites were characterized by X-ray diffraction (XRD), UV-Vis absorption spectroscopy, transmission electron microscopy (TEM), inductively coupled plasma optical emission spectrometry (ICP-OES) and electrochemical impedance spectroscopy (EIS). It was confirmed that the addition of lanthanum oxide did not much affect the crystallinity, crystal structure and the morphology of P25 TiO2. The catalytic activities of the lanthanum oxide/P25 TiO2 catalysts were tested by using 2,4-dichlorophenoxyacetic acid (2,4-D) as the test pollutant and UV light as the irradiation source. The reaction was caried out for 1 hour at room temperature and the percentage removal was determined using a UV spectrophotometer. The results showed that La loading was an important factor that influenced the photocatalytic activity of the composites. After 1 hour reaction, the best catalyst with 0.1 mol% of La loading showed 24% higher photocatalytic activity than the unmodified P25 TiO2 catalyst. It is shown by EIS that the enhanced photocatalytic activity of the composites was due to the ability of lanthanum oxide in improving the charge separation of the photogenerated electron-hole pairs in TiO2