Maximizing the synergistic effect on accelerated photoelectron transfer of TiO2 by double Z-scheme heterojunctions and specific oxygen vacancies

Abstract

Photocatalysis is an ideal technology for environmental applications, but its efficiency is severely limited by slow kinetics and low efficiency of carrier separation. Herein, a photocatalyst (TiO2–Bi2Ti2O7-600 °C) with homotypic growth possessing double Z-scheme heterojunctions was successfully synthesized by the growth of mixed crystalline phase TiO2 on the surface of Bi2Ti2O7. The carrier separation efficiency of the heterojunctions was enhanced by the photo-ferroelectricity of Bi2Ti2O7. Simultaneously, the interface-fused TiO2/Bi2Ti2O7 provided stability for carrier transport between heterojunctions. Modern instrumental characterization confirmed that oxygen vacancies mainly exist in Bi–O structural units provided by Bi2Ti2O7 and that the carrier separation efficiency of the double Z-scheme heterojunctions was significantly higher than that of the single Z-scheme heterojunctions. Density-of-states calculations based on the first principle confirmed that the carrier separation efficiency was higher when the oxygen vacancies presented in the Bi–O structural units than they presented in the Ti–O structural units. TiO2–Bi2Ti2O7-600 °C could accomplish the complete degradation of Rh–B (10 mg/L) in aqueous environment within 80 min, instead of only contributing to the destruction of conjugated chromogenic groups in Rh–B. This photocatalyst with stable structure, multiple carrier transport channels, and sufficient oxygen vacancies enables the photoelectrons to concentrate on the confinement effect, opening a novel avenue for the design strategy of new-generation photocatalysts in environmental wastewater applications.