Band-engineered Zn2TiO4 nanowires for hydrogen generation from water using visible light: A first-principles study

The electronic structure and optical properties of inverse-spinel Zn2TiO4 nanowires and bulk material were investigated for hydrogen generation from water by visible-light photocatalysis using first-principles density calculations. In our theoretical studies, the bandgap of the Zn2TiO4 nanowires was much smaller than that of the bulk material. New intermediate states appeared in the mid-bandgap as a result of Zn and Ti atoms on the surface of ZnO-terminated and ZnTiO-terminated nanowires. These deep-level states could become recombination centers for photogenerated electron–hole pairs, indicating that these two types of nanowires would no longer meet the requirements for photocatalytic water splitting. In contrast, the electronic states arising from oxygen elements on the surface of the TiO-terminated nanowires resulted in an upward movement of the edge of the valence band, whereas the surface electronic states made no difference to the edge of the conduction band. Moreover, the optical property calculations showed that the optical absorption edge of the nanowire would be red-shifted. These calculations revealed that inverse-spinel Zn2TiO4 nanowires were appropriate for visible-light photocatalytic water splitting reactions.