Two-step synthesis of a novel visible-light-driven K2Ta2O6−xNx catalyst for the pollutant decomposition

Visible-light-driven K2Ta2O6−xNx catalysts have been synthesized successfully from N-doped Ta2O5 precursors in KOH solutions by a simple hydrothermal process. K2Ta2O6−xNx with pyrocrhore structure could be obtained at above 160 °C for 24 h. K2Ta2O6−xNx crystals presented cube-shaped morphologies, and absorbed the visible-light up to the wavelength of 600 nm. The as-prepared sample could decompose formaldehyde efficiently under the visible irradiation (λ > 400 nm), and its photocatalytic activity depended on the N-doping content and the hydrothermal temperature. K2Ta2O5.982N0.018 prepared at 220 °C for 24 h showed the highest photoactivity for the formaldehyde degradation. Additionally, it presented much higher activity than that of the sample prepared by the NH3 annealing directly. The visible-light response of K2Ta2O6−xNx catalyst could be closely related to the N-doping content. As the x values were >0.256, the valence-band of the catalyst was composed of the hybrid O 2p and N 2p orbitals, and the visible-light sensitivity was due to the narrowing of the band-gap by mixing the N 2p and O 2p states. However, as the x values were <0.073, the isolated narrow band formed above the valence-band of O 2p was responsible for the visible-light response.