Role of surface oxygen vacancies in zinc oxide/graphitic carbon nitride composite for adjusting energy band structure to promote visible-light-driven photocatalytic activity

Abstract Introducing oxygen vacancies is an effective way to promote photocatalytic performance of catalysts. Numerous explorations on metallic oxides and their composites were aimed at promoting visible light efficiency by narrowing bandgap and enhancing charge separations. In this work, we designed and synthesized the zinc oxide/graphitic carbon nitride (ZnO/g-C3N4) composites with diverse content of surface oxygen vacancies. We investigated the possible correlations between the surface defects and energy band structure using ultraviolet–visible (UV–vis) absorption spectra, Mott-Schottky plots and X-ray photoelectron spectroscopy. The results show that the surface oxygen vacancies in ZnO/g-C3N4 were responsible for the narrowing of the bandgap derived from the lower conduction band of ZnO. Composites of ZnO/g-C3N4 with more surface oxygen vacancies had significantly increased transient photocurrent with higher photocatalytic activity under visible light. The improved photocatalytic activity was demonstrated through photocatalytic organic degradation kinetics. Moreover, the introduction of surface oxygen vacancies in composite was originated from the formation of Zn-C bonds at heterojunctions between ZnO and g-C3N4.