Preparation and characterization of visible-light-driven N–F–Ta tri-doped TiO2 photocatalysts

A new strategy to synthesize visible-light-driven N doped and N–F–Ta tri-doped TiO2 nanocatalysts via a hydrothermal combined with heat treatment method applied in Rhodamine B (RhB) and phenol decomposition was reported. The tri-doped sample gave the highest visible-light photocatalytic activity when the molar ratio of Ta to Ti was 1%. At a low tri-doping level, physicochemical analysis indicated that the synergistic effects of N, F and Ta could effectively increase not only the crystallite surface area but also the light absorption and radical dotOH generation ability, which contributed to the enhancement of visible-light photocatalytic activities. EPR and XPS analysis demonstrated that N–Ta interaction induced the charge compensation to form N 2p–Ta 5d hybridized states which improved the separation ability of the photoexcited electron–hole pairs. Still, F incorporation facilitated the incorporation of N which further promoted the N 2p–Ta 5d hybridized states. The N 2p, π*N–O, oxygen vacancy, Ti3+ and Ta 5d states were also responsible for the band gap narrowing. However, a high tri-doping level would affect the crystal growth and introduce too many defects into the lattice, reducing the visible-light photoactivity.