The electronic structure, optical absorption and photocatalytic water splitting of (Fe + Ni)-codoped TiO₂ : A DFT + U study

The electronic and optical properties of Fe or/and Ni (co)doped anatase and rutile TiO₂ were investigated using the spin-polarized density functional theory. Our calculated results indicate that the synergistic effect of (Fe + Ni) codoping can lead to a band gap narrowing and the hybridized states of Fe 3d and Ni 3d appearing in the forbidden gap, which enhances greatly the optical absorption of TiO₂ nanomaterials from the ultraviolet-light to the infrared-light region and reduces the recombination of photogenerated electron–hole pairs. In particular, (Fe + Ni) codoping can improve greatly the infrared-light absorption of TiO₂ nanomaterials. Furthermore, the researches of electronegativity show that (Fe + Ni)-codoped TiO₂ system has a stronger redox power for hydrogen generation by photocatalytic water splitting compared with pure, Fe-doped, and Ni-doped TiO₂ systems. These results lead to an outstanding solar energy photocatalytic water splitting for hydrogen generation in (Fe + Ni)-codoped TiO₂ photocatalyst.