Introducing oxygen vacancies in TiO₂ lattice via trivalent iron to enhance photocatalytic removal of indoor NO

The synthesis of oxygen vacancies (OVs) modified TiO₂ under mild conditions is attractive. In this work, OVs were easily introduced in TiO₂ lattice during the hydrothermal doping process of trivalent iron ions. Theoretical calculations based on a novel charge-compensation structure model were employed with experimental methods to reveal the intrinsic photocatalytic mechanisms of Fe doped TiO₂ (Fe-TiO₂). The OVs’ formation energy in Fe-TiO₂ (1.12 eV) was only 23.6% of that in TiO₂ (4.74 eV), explaining why Fe³⁺ doping could introduce OVs concentration in TiO₂ lattice. The calculation results also indicated that impurity states introduced by Fe³⁺ and OVs enhanced the light absorption activity of TiO₂. Additionally, the charge carriers’ transport was investigated by carriers’ lifetime and relative mass. The carriers’ lifetime of Fe-TiO₂ (4.00 ns, 4.10 ns and 3.34 ns for 1%, 2% and 3% doping concentration, respectively) was longer than that of undoped TiO₂ (3.22 ns), indicating Fe³⁺ and OVs could promote the separation of charge carriers, which can be attributed to the bigger relative effective mass of electrons and holes. Herein, the Fe-TiO₂ has higher photocatalytic indoor NO removal activity compared with other photocatalysts because it has strong light absorption activity and high carriers’ separation efficiency.