Artículos SCI

MnOx, CeO2, and MnCe-O (Mn/Ce = 1) solids have been prepared via the citrate complexation and combustion method using citrate and urea precursors. The solids have been characterized by XRD, SEM-EDX, N-2-adsorption-desorption, UV-Vis spectroscopy, TPR, O-2-TPD, and XPS techniques. The catalytic reactivity of the manganese oxides was not affected by the preparation protocol. In the case of ceria and mixed oxides, the synthesis method greatly affected the structural and chemical properties, ultimately altering their reactivity. The citrate complexation method produced the most homogeneous and active mixed oxide, whereas the urea combustion method resulted in less active solids. The mixed oxide prepared via urea combustion was less active than the manganese single oxide; the decrease in activity was attributed to phase separation and the formation of Mn3O4 domains on the surface of ceria. In contrast, citrate complexation resulted in solids with the lowest particle size (similar to 3 nm), the highest oxidation state for manganese, and the highest proportion of oxygen vacancies, which promote the oxidation reaction.

The morphology and void connectivity of thin films grown by a magnetron sputtering deposition technique at oblique geometries were studied in this paper. A well-tested thin film growth model was employed to assess the features of these layers along with experimental data taken from the literature. A strong variation in the film morphology and pore topology was found as a function of the growth conditions, which have been linked to the different collisional transport of sputtered species in the plasma gas. Four different characteristic film morphologies were identified, such as (i) highly dense and compact, (ii) compact with large, tilted mesopores, (iii) nanocolumns separated by large mesopores, and (iv) vertically aligned sponge-like coalescent nanostructures. Attending to the topology and connectivity of the voids in the film, the nanocolumnar morphology was shown to present a high pore volume and area connected with the outside by means of mesopores, with a diameter above 2 nm, while the sponge-like nanostructure presented a high pore volume and area, as well as a dense network connectivity by means of micropores, with a diameter below 2 nm. The obtained results describe the different features of the porous network in these films and explain the different performances as gas or liquid sensors in electrochromic applications or for infiltration with nanoparticles or large molecules.