A continuous valence band through N-O orbital hybridization in N-TiO2 and its induced full visible-light absorption for photocatalytic hydrogen production

Photocatalytic hydrogen production represents an effective approach for solar energy conversion, which can greatly ease the current energy crisis. Herein, we report a successful N-O orbital hybridization in N-doped TiO2 nanotube, the absorption wavelength is greatly red-shifted to visible light (from 400 to 800 nm) with large absorbance. The doping N element can partially replace the oxygen sites in TiO2 lattice to form N-Ti-N bonds. The hybridization effect of N 2p and O 2p makes a continuous valence band and the position up-shift from 1.99 to 1.67 eV, the band gap is subsequently narrowed from 3.21 to 2.77 eV for 1.85-N-TiO2 nanotube, which has been confirmed by ultraviolet-visible diffuse reflectance spectra and X-ray photoelectron spectroscopy valence band spectra. Benefiting from the enhanced visible light absorption ability and ultrathin shell feature, 1.85-N-TiO2 nanotube exhibits exciting photocatalytic hydrogen evolution performance with a rate of 10870 mu mol h(-1) g(-1) under the selected visible light irradiation (lambda > 400 nm). This work demonstrates an alternative strategy for tuning visible light absorption ability by doping for wide-band-gap semiconductors in photocatalysts design, and the philosophy can also be extended to other photocatalytic systems. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.