Abstract
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.
NSTL
Elsevier