The synthesis and characterization of ytterbium-doped TiO2 hollow spheres with enhanced visible-light photocatalytic activity

Abstract

Using (C₁₆H₃₆O₄)Ti and Yb(NO₃)₃ solutions as raw materials, Yb-doped TiO₂ hollow spheres (Yb-TiO₂HS) with different doping ratios (Yb : Ti = 0.5%, 1%, and 1.5%) were successfully fabricated via a sol–gel template method with melamine–formaldehyde polymer microspheres (MF) as templates. The Yb-TiO₂HS were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, specific surface area and porosity analysis, ultraviolet-visible-light diffused reflection spectroscopy (UV-DRS), and luminescence spectroscopy. The Yb-TiO₂HS can absorb visible-light and exhibit a lower recombination of electrons (e⁻) and holes (h⁺) when compared with commercial P25 TiO₂ powder (P25). The photocatalytic activities of the prepared samples were estimated by the degradation process of methyl orange (MO) dye under irradiation with visible-light (λ > 450 nm). With H₂O₂ and Yb-TiO₂HS (Yb : Ti = 1%) as the promoter and photocatalyst, respectively, the degradation ratio of MO achieved a maximum value (89%) after irradiation for 5 h. While excessive Yb doping resulted in a negative effect on the photocatalysis, an appropriate doping ratio restrained the recombination of electron–hole pairs and extended the light absorption range, thus enhancing the ability of the visible-light photocatalysis. Moreover, the addition of H₂O₂ improved the dye adsorptive activity of TiO₂HS, which further enhanced the photocatalytic effect.