Ni2+ and Ti3+ co-doped porous black anatase TiO2 with unprecedented-high visible-light-driven photocatalytic degradation performance

Abstract

A novel Ni²⁺ and Ti³⁺ co-doped porous black anatase TiO₂ is successfully synthesized by a facile sol–gel technique combined with an in situ solid-state chemical reduction approach, followed by mild calcinations (350 °C) in argon atmosphere. The obtained photocatalysts are characterized in detail by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance, N₂ adsorption, and transmission electron microscopy. The results indicate that the Ni²⁺ and Ti³⁺ elements are co-doped into the lattice of anatase TiO₂. The prepared Ni²⁺/Ti³⁺ co-doped black anatase TiO₂ possesses a mesoporous structure, consisting of disordered Ti³⁺ and oxygen vacancy layers. Based on UV-vis diffuse reflectance spectra and valence band analysis, the doped Ni²⁺ and Ti³⁺ species can significantly narrow the band gap of anatase TiO₂ due to the formation of mid-gap states, which allows utilization of visible-light and prevents fast recombination of photogenerated charges effectively. Furthermore, the prepared co-doped photocatalysts exhibit unprecedented higher photocatalytic activity than that of the pure TiO₂ and the Ni²⁺ doped TiO₂. The degradation ratio of methyl orange and rhodamine B is up to 95.38 and 95.86%, respectively, within 150 min irradiation of visible-light by the obtained Ni²⁺/Ti³⁺ co-doped porous black anatase TiO₂. The high visible-light photocatalytic degradation performance may be ascribed to the efficient doping of Ni²⁺ and Ti³⁺ in favor of the absorption of visible-light and the separation of photogenerated charges, and the porous structure facilitating the diffusion of reactants and products.