Characterization and photocatalytic activity of Fe- and N-co-deposited TiO2 and first-principles study for electronic structure

Titanium dioxide (TiO2), co-deposited with Fe and N, is first implanted with Fe by a metal plasma ion implantation (MPII) process and then annealed in N2 atmosphere at a temperature regime of 400–600 °C. First-principle calculations show that the (Fe, N) co-deposited TiO2 films produced additional band gap levels at the bottom of the conduction band (CB) and on the top of the valence band (VB). The (Fe, N) co-deposited TiO2 films were effective in both prohibiting electron–hole recombination and generating additional Fe–O and N–Ti–O impurity levels for the TiO2 band gap. The (Fe, N) co-deposited TiO2 has a narrower band gap of 1.97 eV than Fe-implanted TiO2 (3.14 eV) and N-doped TiO2 (2.16 eV). A significant reduction of TiO2 band gap energy from 3.22 to 1.97 eV was achieved, which resulted in the extension of photocatalytic activity of TiO2 from UV to Vis regime. The photocatalytic activity and removal rate were approximately two-fold higher than that of the Fe-implanted TiO2 under visible light irradiation.