Band-to-Band Visible-Light Photon Excitation and Photoactivity Induced by Homogeneous Nitrogen Doping in Layered Titanates

Abstract

The distribution of dopants in semiconductors can intrinsically determine the electronic structure and consequently the absorbance, redox potential, and charge-carrier mobility of the semiconductor photocatalysts. In contrast to most reported nitrogen-doped titania photocatalysts with some localized states in the intrinsic band gap and small visible light absorption shoulders induced by inhomogeneous nitrogen doping near the particle surface, we report here the homogeneous substitution of O by N in the whole particles of layered titanates. The resultant materials Cs 0.68 Ti 1.83 O 4− x N x exhibited extraordinary band-to-band excitation in the visible-light ranging up to blue light. From photoelectron spectroscopy and first-principles calculations, the upward shift of valence band maximum by N 2p states is concluded as the cause of the band-to-band visible light excitation. The holes generated upon visible light excitation in the newly formed valence bands of Cs 0.68 Ti 1.83 O 4− x N x and H 0.68 Ti 1.83 O 4− x N x had strong oxidation ability in oxidizing OH − into active •OH radicals in photocatalysis. These findings are the clear evidence for the substantial role of homogeneous nitrogen doping in obtaining band-to-band visible-light photon excitation in layered titanates. The new physical insights into the electronic structure of homogeneous substitutional N in layered titanates gained here may have important implications for developing other efficient visible light photocatalysts by nonmetal doping.