Synthesis and characterization of La 2O 3/TiO 2− xF x and the visible light photocatalytic oxidation of 4-chlorophenol

Abstract

In this work, we investigated the synergetic effect of La and F on the visible light photocatalytic activity of TiO 2 catalysts. La 2O 3/TiO 2− x F x photocatalysts were prepared by a simple sol-gel process using tetrabutyl titanate (TBT), La(NO 3) 3 and NH 4F as precursors. XPS results revealed that La 2O 3 accumulated on the surface of TiO 2, which enhanced the surface area of TiO 2 and inhibited the recombination of electron–hole pairs. It also showed that two kinds of fluorine species were formed and these increased the acid active sites and enhanced the oxidation potential of the photogenerated holes in the valance band. UV–vis diffuse reflection spectra of La 2O 3/TiO 2− x F x showed that intraband gap states were present and these are probably responsible for its absorption of visible light while the intrinsic absorption band was shifted slightly to a longer wavelength. At molar ratios of La and F to Ti of 1.5:100 and 5:100 and after calcination at 500 °C, the degradation rate of 4-chlorophenol (4-CP) over the sample was about 1.2–3.0 times higher than that of the other doped samples and undoped TiO 2. The total organic carbon (TOC) removal rates of 4-CP showed that 4-CP was mineralized efficiently in the presence of the sample under visible light illumination.