Ceria (CeO₂) plays a vital role in emerging technologies for environmental and energy-related applications. The catalytic efficiency of ceria nanoparticles depends on its morphology. In this study, CeO₂ nanoparticles were synthesized by a microwave-assisted hydrothermal method under different synthesis temperatures. The samples were characterized by X-ray diffraction, transmission electron microscopy, Raman scattering spectroscopy, electron paramagnetic resonance spectroscopy and by the Brunauer–Emmett–Teller method. The X-ray diffraction and Raman scattering results indicated that all the synthesized samples had a pure cubic CeO₂ structure. Rietveld analysis and Raman scattering also revealed the presence of structural defects due to an associated reduction in the valence of the Ce⁴⁺ ions to Ce³⁺ ions caused by an increasing molar fraction of oxygen vacancies. The morphology of the samples was controlled by varying the synthesis temperature. The TEM images show that samples synthesized at 80 °C consisted of spherical particles of about 5 nm, while those synthesized at 120 °C presented a mix of spherical and rod-like nanoparticles and the sample synthesized at 160 °C consisted of nanorods with 10 nm average diameter and 70 nm length. The microwave-assisted method proved to be highly efficient for the synthesis of CeO₂ nanoparticles with different morphologies.

We report herein a detailed study on the influence of microwave-assisted hydrothermal (MAH) treatment time on both long and short range structures around Ti atoms of SrTiO₃ powders. Few studies have been carried out on short-order structural properties as well as the relationship between the local order and the SrTiO₃ photocatalytic properties. We use X-ray diffraction to determine the long-range structure, while the local environment around the Ti atom is probed with X-ray absorption spectroscopy and the vibration frequencies are investigated by Raman spectroscopy. The faster crystallization of SrTiO₃ powders provided by the MAH system resulted in large distortions of Ti–O bond lengths which remain unchanged even for a longer MAH treatment time. Despite the long-range structure being associated with ideal TiO₆ clusters, X-ray absorption spectroscopy measurements identified the presence of undercoordinated TiO₅ clusters. Compared with the reference bulk SrTiO₃, the hierarchical SrTiO₃ cube-like shape showed enhanced photocatalytic activity, which was associated with the presence of these TiO₅ clusters. Field emission scanning electron microscopy (FE-SEM) revealed that the superstructures based on a cube-like shape are formed by an assembly process, becoming well defined as a function of MAH treatment time.