Characterization and Computation of Yb/TiO₂ and Its Photocatalytic Degradation with Benzohydroxamic Acid

Yb-doped TiO₂ (Yb/TiO₂) compositions were synthesized by sol-gel method, and the prepared materials were characterized by X-ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-visible diffuse-reflectance spectrum (UV-Vis DRS), transmission electron microscope (TEM) and high resolution transmission electron microscope (HRTEM), energy dispersive spectrometer (EDS), and N₂ adsorption. A beneficiation reagent of benzohydroxamic acid (BHA) was used to test the photocatalytic activity of Yb/TiO₂. The characterizations indicate that the doping of Yb could inhibit the crystal growth of TiO₂, enhance the specific surface area, increase the binding energy of Ti2p, and also slightly expand the adsorption ranges to visible light. Furthermore, the computation of band structure also indicates that Yb-doped TiO₂ could make the forbidden band narrower than pure anatase TiO₂, which presents a red shift in the absorption spectrum. As a result of the photodegradation experiment on BHA, Yb/TiO₂ (0.50% in mass) sintered at 450 °C displayed the highest catalytic activity for BHA when compared with pure TiO₂ or other doped Yb/TiO₂ compositions, and more than 89.2% of the total organic carbon was removed after 120 min. Almost all anions, including Cl^-, HCO₃^-, NO₃^-, and SO₄^2-, inhibited the degradation of BHA by Yb/TiO₂, and their inhibition effects followed the order of HCO₃^- > NO₃^- > SO₄^2- > Cl^-. Cations of Na⁺, K⁺, Ca²⁺, and Mg²⁺ displayed a slight suppressing effect due to the impact of Cl^- coexisting in the solution. In addition, Yb/TiO₂ maintained a high photocatalytic ability with respect to BHA after four runs. It is hypothesized that ·OH is one of the main species involved in the photodegradation of BHA, and the mutual transformation of Yb³⁺ and Yb²⁺ could promote the separation of electron-hole pairs.