Here we combined experimental and theoretical results to correlate the morphological, optical, and electronic properties of cerium oxide (CeO2) prepared by a microwave-assisted hydrothermal method with varying synthesis times. X-ray diffraction confirmed a cubic structure without deleterious phases. Density functional theory simulations confirmed an indirect (K-L) bandgap energy of 2.80 eV, with an electron transition between O-2p and Ce-4f orbitals, which agrees with the value obtained using diffuse reflectance. Raman spectroscopy shows that changing the synthesis times results in samples with different defect densities at a short range. Theoretical calculations confirmed that the deformations and changes in the experimental Raman spectra area result in oxygen displacement; as the displacement decreases, the crystallinity increases, and only one peak was observed. Scanning electron microscopy and high-resolution transmission electron microscopy show changes in the morphologies as the synthesis time varies. For shorter times, sheet and polyhedral morphologies were noted. With time increases, the sheets turn into nanorods and nanowires until the nanowires decrease and cubes are observed. In addition, an initial study regarding the influence of the surface on the electric response of CeO2 was completed. It was observed that the presence of different surface defects ([CeO6·2Vo x ] or [CeO7·Vo x ]) can alter the material resistance.

Currently, numerous properties of semiconducting oxides are correlated to their morphological characteristics resulting from their exposed surfaces. In the present work, the relationship between the following morphologies rod, bean, hexagon, and rod/cube of CeO2 with the exposure of (111), (110), (100), and (311) surfaces and the main charge carriers generated by the photochemical processes was investigated. This was done in regard to the degradation of ciprofloxacin and rhodamine-B. The initial stages of the degradation of the two types of molecules were evaluated, allowing the determination of where the charge carriers generated in the semiconductor preferentially acted on the molecules. Therefore, the active species in each photocatalyst were identified by scavenger tests and correlated to the computational simulations using the density functional theory. Accordingly, the relationships between the morphology, surface exposure in the particles, surface defects, photochemically generated species, and preferential attack on the micropollutant molecule were shown. Specific surface area analyses demonstrate an effective relationship between photocatalytic activity and the exposed surface of the particle. This will allow rationalization of the relation between the catalytic and electronic properties of semiconductor surfaces.

Here we present an easy-reproducible microwave-assisted hydrothermal route for preparing pure nanocrystalline CeO 2 films. The produced materials were characterized using a wide range of techniques (X-ray diffraction, field emission gun scanning electron microscopy, Raman spectroscopy) to understand the synthesis dependent changes in crystallographic structure, and crystallite size. Raman and X-ray diffraction techniques revealed that the films were free of secondary phases and that they crystallize in the cubic structure. The observed hydrodynamic particle size larger than the crystallite size confirms the aggregation phenomenon. Gas sensing measurements have been carried out to rationalize the type and number of surface adsorbed groups and overall nanostructure.Electrical conductance variations, owing to gases adsorption onto semiconductor oxide films surfaces, were observed in this work. Chemiresistive CeO 2 film properties depend on the intergranular barrier heights and width.

In this work, a high photocatalytic activity was attained by intercalating a Pt layer between SnO 2 and TiO 2 semiconductors, which yielded a TiO 2 /Pt/SnO 2-type heterostructure used in the discoloration of blue methylene (MB) solution. The porous films and platinum layer were obtained by electrophoretic deposition and DC Sputtering, respectively, and were both characterized morphologically and structurally by FE-SEM and XRD. The films with the Pt interlayer were evaluated by photocatalytic activity through exposure to UV light. An increase in efficiency of 22% was obtained for these films compared to those without platinum deposition. Studies on the reutilization of the films pointed out high efficiency and recovery of the photocatalyst, rendering the methodology favorable for the construction of fixed bed photocatalytic reactors. A proposal associated with the mechanism is discussed in this work in terms of the difference in Schottky barrier between the semiconductors and the electrons transfer and trapping cycle. These are fundamental factors for boosting photocatalytic efficiency.

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