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

As one of the most significant rare-earth oxides, cerium dioxide (ceria, CeO2) has an enormous potential in a variety of materials science applications due to many excellent characteristics. In this work, cubic-phase mesoporous CeO2 (mCeO2) nanospheres with nanocrystalline frameworks, high Ce3+ 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 N2 adsorption-desorption analyses. Raman and XPS results confirmed the presence of Ce4+, Ce3+ and Zr4+ ions and oxygen vacancies. By comparison with the undoped ones, Zr-doping in mCeO2 nanospheres contributed to increased concentrations of Ce3+ (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 mCeO2 nanospheres were evaluated with the degradation of methylene blue (MB) under visible-light irradiation. The Zr-doped mCeO2 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 mCeO2 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 mCeO2 nanospheres were also proposed. This work is expected to provide an insight view into the design and synthesis of low-cost and high-efficiency CeO2-based photocatalysts with improved visible photocatalytic activity.