Evolution of Visible Photocatalytic Properties of Cu-Doped CeO2 Nanoparticles: Role of Cu2+-Mediated Oxygen Vacancies and the Mixed-Valence States of Ce Ions

Abstract

We report the contribution of oxygen vacancies for enhancing the optical and visible photocatalytic properties of Cu-doped CeO2 nanoparticles (NPs) synthesized through a low-temperature coprecipitation method. Doping Cu ions in the ceria lattice in different mole percentages, 0, 3, 5, 7, 9, and 15 wt %, results in enhancement of visible photocatalytic properties even under natural sunlight. Transmission electron microscopy and X-ray diffraction studies showcase the monodispersive nature of Cu-doped CeO2 NPs in the size range of 3–7 nm with face-centered cubic structure. The Cu-based defect states induce a narrow band function in ceria nanostructures and influence the red shift in absorption with the Cu concentrations. Visible photocatalytic degradation of methylene blue was investigated in the presence of pure CeO2 NPs, CuO NPs, and Cu-doped CeO2 NPs. These studies revealed that the 7 wt % of Cu-doped CeO2 NPs exhibit the degradation rates of 1.41 × 10–2 and 1.12 × 10–2 min–1 under exposure to natural sun...