Stable yellow ZnO mesocrystals with efficient visible-light photocatalytic activity

Abstract

Band-gap narrowing is of significance and an advantage for potential visible-light photocatalytic applications. Here we report an effective strategy for the large-scale synthesis of yellow ZnO mesocrystals with a narrow band-gap (E_g = 3.09 eV) and visible-light response using the Zn(OH)F precursor. Raman and X-ray photoelectron spectroscopy (XPS) spectra reveal that a large amount of oxygen vacancies exist in the yellow ZnO mesocrystals, and that the concentration of oxygen defects decreases with an increase of the annealing temperature in air. Oxygen vacancies result in a narrowing of the band-gap and an increase the visible-light response of the yellow ZnO. Electron paramagnetic resonance (EPR) spectra confirm that abundant surface defects exist in yellow ZnO, leading to strong photoluminescence emission. The yellow ZnO mesocrystals are found to be efficient for the photodecomposition of methyl blue (MB) under visible-light irradiation. It is demonstrated that highly ordered porous mesocrystals are favorable for directional transport and highly efficient separation of charge carriers. Notably, our yellow ZnO microring sample is very stable for at least one year. Therefore, our present work highlights the feasibility of the simultaneous engineering of oxygen vacancies and visible-light response for the design of novel ZnO-based materials for solar energy conversion.