Facile Fabrication of N-Doped K2Nb2O6 Nanocrystals with Defective Pyrochlore Structure for Improved Visible-Light Photocatalytic Hydrogen Production

Semiconductor-based photocatalytic water splitting is one of the effective ways for future hydrogen (H-2) production. However, the wide bandgap of most semiconductors severely limits the solar spectral absorption range, which seriously hinders their practical applications. Herein, porous N-doped K2Nb2O6 nanocrystals with defective pyrochlore structure are rationally designed to extend the absorption range from ultraviolet to visible region around 550 nm by NH3 heat treatment. The obtained 6N-K2Nb2O6 shows the highest visible-light activity with an H-2 evolution rate of 20.4 mu mol h g(-1). More detailed exploration demonstrates that NH3 heat treatment can promote the substitutional nitrogen doping in K2Nb2O6 crystals while accompanied by the formation of oxygen vacancies or Nb4+ species. The hybridization of N 2p and O 2p orbitals in the valence band (VB) of the nitrogen-doped K2Nb2O6 makes the VB maximum move more negatively, whereas the conduction band minimum shifted more positively due to the role of defective Nb4+ species. Such a synergistic effect endows the samples with visible-light absorption and greatly enhances charge separation and transfer efficiency, resulting in the excellent H-2 production performance. This study provides additional insights into the understanding of the effect of nitrogen doping on photocatalysts with excellent visible-light-driven photocatalytic activity.

Automated summary

This study reports the rational design of porous N-doped K2Nb2O6 nanocrystals to extend the absorption range and enhance the visible-light activity for photocatalytic water splitting. The nitrogen doping and the presence of defective Nb4+ species result in a synergistic effect that improves charge separation and transfer efficiency. This study contributes to a better understanding of the effect of nitrogen doping on photocatalysts with visible-light-driven photocatalytic activity.