Rendering Visible-Light Photocatalytic Activity to Undoped ZnO via Intrinsic Defects Engineering

It is significant to render visible-light photocatalytic activity to undoped ZnO nanostructures via intrinsic defect engineering. In this work, undoped ZnO nanocrystals were derived via co-precipitation synthesis. The resulting ZnO nanocrystals were characterized by means of X-ray diffraction, scanning electron microscopy, photoluminescence spectroscopy, and ultraviolet-visible absorption spectroscopy, respectively. The visible-light photocatalytic activity of the products were characterized by monitoring the decomposition of methyl orange in water under visible-light illumination of a 300 W halogen lamp. It is found that undoped ZnO nanocrystals exhibit visible-light photocatalytic activity with their first-order rate constant up to 4.6 x 10(-3) min(-1). Density functional calculations show that oxygen vacancies create deep energy levels at E-V + 0.76 eV in the bandgap of ZnO. In conjunction with the density functional calculations, the photocatalytic degradation of methyl orange under visible-light irradiation provides direct evidence that oxygen vacancies in ZnO nanocrystals yield the visible-light photocatalytic activity. Our results demonstrate that visible-light photocatalytic activity can be endowed to undoped ZnO nanocrystals by manipulating the intrinsic defects in ZnO. Intrinsic defect-modulated ZnO photocatalysts thus represent a powerful configuration for further development toward visible-light responsive photocatalysis.