Double-Hole-Mediated Codoping on KNbO3 for Visible Light Photocatalysis.

Abstract

In this theoretical study, the double-hole-mediated codoping strategy has been adopted to improve the photocatalytic activity of cubic KNbO3 as compared with the corresponding individual doping. The strong double-hole-mediated dopant-dopant coupling significantly reduces the effective bandgaps for the anionic-anionic (N-N, P-P, N-P, C-S) codoped systems with removing the appearing acceptor states above the Fermi level. No dopant-O coupling occurs in the cationic-anionic (V-C, Ti-P, Ti-N, Zr-P, Zr-N, Sc-S, Y-S) codoped systems. The V-C and Ti-P codoping could lead to narrowed bandgaps without unfilled localized states appearing above the Fermi level. N, Ti, Zr, Sc, Y monodoping and Ti-N, Zr-P, Zr-N, Sc-S, Y-S codoping introduce unoccupied impurity states between the valence band maximum and conduction band minimum, which makes them unfavorable for photocatalysis as these impurity states may serve as electron-hole recombination centers. For P-P, N-P, and C-S codoped systems, the intermediate states are higher or close to the hydrogen evolution potential, which is thermodynamically unfavorable for production of both oxygen and hydrogen. Producing hydrogen only, the N-N and C-S codoped KNbO3 materials will be good choices for Z-scheme photocatalysis. V, S, and V-C codoped KNbO3 may be promising visible light photocatalysts for water splitting, as they have suitable effective bandgaps without the introduction of unoccupied impurity states above the Fermi level, and they also own proper band edge positions with respect to the water redox level. The calculated optical absorption curves also indicate that C, V, and S monodoping and N-N, V-C, and Ti-P codoping can effectively enhance the visible light absorption.