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

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.