Highly active amorphous nitrogen-doped niobium oxide for deep photocatalytic oxidation of NO under visible light

A series of amorphous nitrogen-doped niobium oxide (X-N-Nb₂O₅, X = 2, 3, 4) was synthesized via high-temperature annealing under an ammonia atmosphere. Their photocatalytic performance for deep NO oxidation under visible light was systematically evaluated. Nitrogen doping effectively narrowed the band gap by introducing impurity energy levels, enhanced visible-light absorption responsiveness and improved photogenerated charge separation efficiency. By inducing oxygen vacancies (OVs), nitrogen doping improved the surface reactivity toward NO and O₂ adsorption and activation. Among the as-prepared samples, 3-N-Nb₂O₅ exhibited the highest NO removal efficiency and excellent cyclic stability, maintaining 80 % conversion after five cycles under 50 % relative humidity, with markedly suppressed NO₂ generation. In-situ DRIFTS and EPR analyses revealed the enhanced production of reactive oxygen species and provided insights into the reaction mechanism. This work offers a promising strategy for designing visible-light-responsive photocatalysts for air purification.