Effect of metal-ion doping on the characteristics and photocatalytic activity of TiO₂ nanotubes for the removal of toluene from water

Toluene is an extensively used reagent that could cause water pollution and endanger human health. In this work, an O₃/UV/ion-doped TiO₂ nanotubes process was investigated to obtain the optimum TiO₂ nanotubes for effective toluene decomposition. Photocatalytic activity is found to be influenced by the doped-ion type by affecting the ionic radius, valence state, and configuration of the dopant. The calcination temperature and doping concentration, which change the weight fractions of the anatase phase (f_A), the Brunauer–Emmett–Teller surface area (S_BET), and the energy band gap (E_g) of the catalyst, also affect the photocatalytic activity. When TiO₂ is doped with ions, S_BET decreases and E_g becomes narrower. The photocatalytic activities of TiO₂ for toluene removal increase after doping with Ag⁺, Al³⁺, Cu²⁺, Fe³⁺, Mn²⁺, Ni²⁺, V⁵⁺, and Zn²⁺. Moreover, the 1.0% Fe³⁺-doped TiO₂ nanotubes calcined at 550 °C have the highest catalytic activity, with a toluene removal efficiency of 70.7%.