Visible-light-active mesoporous ceria (CeO2) nanospheres for improved photocatalytic performance

As one of the most significant rare-earth oxides, cerium dioxide (ceria, CeO 2 ) has an enormous potential in a variety of materials science applications due to many excellent characteristics. In this work, cubic-phase mesoporous CeO 2 (mCeO 2 ) nanospheres with nanocrystalline frameworks, high Ce 3+ and oxygen vacancy contents, large porosity and specific surface area, were fabricated via a facile solvothermal method using inorganic precursors and without surfactant as a template. The resulting products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV–vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy , photoluminescence (PL) spectroscopy, and N 2 adsorption-desorption analyses. Raman and XPS results confirmed the presence of Ce 4+ , Ce 3+ and Zr 4+ ions and oxygen vacancies. By comparison with the undoped ones, Zr-doping in mCeO 2 nanospheres contributed to increased concentrations of Ce 3+ (45.25% vs 32.64%) and oxygen vacancy (37.63% vs 27.53%), as well as decreased band gap energies (2.9 vs 3.1 eV). The photocatalytic activities of the pure and Zr-doped mCeO 2 nanospheres were evaluated with the degradation of methylene blue (MB) under visible-light irradiation. The Zr-doped mCeO 2 products exhibited a superior photodegradation rate of ca. 94% after 120 min visible-light illumination. A kinetic study suggested that the reaction followed pseudo-first order rate equation. The optimizations on Zr-doped mCeO 2 nanospheres against structural, optical, and physicochemical properties might be responsible for the enhanced visible-light-driven photocatalytic performance. The plausible photodegradation mechanism over MB dyes of mCeO 2 nanospheres were also proposed. This work is expected to provide an insight view into the design and synthesis of low-cost and high-efficiency CeO 2 -based photocatalysts with improved visible photocatalytic activity.