Fast and continuous obtaining of Eu³⁺ doped CeO₂ microspheres by ultrasonic spray pyrolysis: characterization and photocatalytic activity

In this work, CeO₂:xEu³⁺ (x = 0, 0.01, 0.02, 0.04 and 0.08 mol%) microspheres were obtained by the fast and continuous ultrasonic spray pyrolysis method. Powders were characterized by X-ray diffraction (XRD), X-ray fluorescence analysis (XRF), scanning electronic microscopy (FESEM), Raman spectra, UV–Visible spectroscopy (UV–Vis) and photocatalytic activity. All XRD patterns were indexed by the cubic structure of the fluorite type, without the presence of secondary phases, indicating success in the Eu³⁺ doping in the CeO₂ structure. In addition, The XRF analysis confirmed the presence of Eu in the CeO₂ powders. In the Raman spectra of the samples occurs the vibrational mode F_2g, which is a characteristic band of materials with the fluorite type structure. Moreover, as the Eu³⁺ ion increased, it was noticed the appearance of additional bands referring to oxygen vacancies. FESEM showed that the CeO₂:xEu³⁺ particles have a spherical morphology with homogeneous chemical composition and particle size between 73 and 1560 nm. It can be seen a slight increase of defects in their morphology as the Eu³⁺ ion increases. The band gap varies between 3.22 and 3.28 eV, being influenced by defects in oxygen vacancies and the concentration of Ce³⁺ ion. The addition of Eu³⁺ generates the introduction of intermediary levels in the conduction band of CeO₂, besides increasing the reactive species effects, favoring the photocatalysis of Rhodamine B dye.