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

Qiang Fu,Lei Guo

doi:10.1063/5.0073968

Abstract

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.

Highlights

Since the first production of hydrogen on crystalline TiO2 as a photocatalyst in 1972,1 photocatalytic water splitting has attracted global interest because it offers feasible, pollution-free hydrogen production
The absorption edge at ∼550 nm in the visible-light spectrum was ascribed to the surface state, which enables a high photocatalytic efficiency in the visible-light spectrum. These results indicate that the TiO-terminated nanowire will exhibit visible optical absorption compared with the bulk material for photocatalytic water-splitting applications
We have examined the impact of the electronic state of the surface atoms of the inverse-spinel Zn2TiO4 nanowires on their electronic and optical absorption

Summary

INTRODUCTION

Since the first production of hydrogen on crystalline TiO2 as a photocatalyst in 1972,1 photocatalytic water splitting has attracted global interest because it offers feasible, pollution-free hydrogen production. The hydrogen production efficiencies of these current photoactive materials are too low for practical application because of high electron–hole recombination rates and poor visible-light absorption. Most crucially, these photocatalysts have bandgaps that are too wide to make use of visible light for hydrogen production. To decrease the large bandgap and enable the use of solar energy, various ions have been used to dope TiO2, which is generally applied in bandgap engineering.16–21 These doped ions can become the recombination centers for the photogenerated electron–hole pairs, which reduces the efficiency of hydrogen production.. Scitation.org/journal/adv has similar energy levels to the photocatalytic water-splitting reaction, a similar band structure to TiO2, and does not artificially introduce defects or recombination centers.. We believe that this research will provide a theoretical basis for identifying and developing suitable photocatalysts with an appropriate bandgap for water-splitting reactions

Structure of Zn2TiO4 nanowires

Computational details

Structural properties of Zn2TiO4 nanowires

Electronic band structure

Absorption properties

CONCLUSIONS