Publications

Surface- and bulk-phosphated ceria catalysts were prepared and studied in propane oxidative dehydrogenation (ODH) at 823 and 873K. The catalysts were characterized by N2 adsorption at 77K, XRD, TEM, and diffuse reflectance IR Fourier transform (DRIFT), Raman, X-ray photoelectron (XPS), and energy dispersive X-ray (EDX) spectroscopies. Both series of catalysts presented an increase in the ODH selectivity with respect to pure ceria mainly at the expense of total oxidation selectivity. Thus, the selectivity to propene was approximately 74% with surface-phosphated catalysts and 62% with bulk-phosphated catalysts. For the surface-phosphated samples, P is confined to the surface and subsurface regions of the ceria particles, whereas P is also dispersed in the bulk of the oxide in the bulk-phosphated samples. Finally, all the characterization techniques led us to the conclusion that Ce4+ cations that interact with P are responsible for the observed increase in the ODH.

Monodisperse core-shell hybrid nanoparticles based on cobalt ferrite (CoFe2O4) particles coated with polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG) biopolymers were obtained employing a two-step procedure: the CoFe2O4 of 21 nm mean particle size were first synthesized by coprecipitation method assisted by PVP soft template and then were coated by PVP or PEG biopolymers. The effect of the thermal treatment upon the phase evolution of the obtained precursor from the coprecipitation step was monitored by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses. The FTIR spectra also indicated the interaction between the cobalt ferrite particles and the two polymers were used as bio-compatible coatings. Transmission electron microscopy (TEM) and Selected Area Electron Diffraction (SAED) analyses revealed the formation of approximately 22 nm CoFe2O4-PVP and CoFe2O4-PEG hybrid nanoparticles. The magnetic measurements indicated that all synthesized hybrids were appropriate for applying in biomedical field. Testing the bioeffect of the uncoated cobalt ferrite nanoparticles and corresponding hybrids on Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli, Salmonella enterica serovar typhimurium bacteria and Candida scotti yeast it was clear that no significant toxic activity was obtained. Moreover, all the prepared nanohybrids and their components possess antioxidant activity. (C) 2012 Elsevier B.V. All rights reserved.

The correlation of the lattice disorder with the nanocrystal average size, in ZnO nanocrystals synthesized by several different methods, has been quantitatively monitored by line shape analysis of the multifrequency electron paramagnetic resonance (EPR) spectra of low concentrations of substitutional Mn2+ probing ions. The observed correlation between the line broadening parameter of the spectrum and the average ZnO nanocrystals size, independent of the synthesis procedure of the ZnO nanocrystals, demonstrates the dominance of the size related strain/disorder. On the basis of this result, a new method for determining the average ZnO nanocrystal size from the quantitative analysis of the EPR spectra of the Mn2+ probes was derived. The nanocrystallization of the disordered ZnO formed by the thermal decomposition of hydrozincite was monitored using this procedure. The observed ZnO nanocrystallite growth kinetics at lower temperatures was described by a structural relaxation mechanism consisting of the local ordering by rearrangements of the atoms in the interfaces/grain boundaries, with a growth activation energy of similar to 23 kJ/mol. When the nanostructured ZnO was more than 75% crystallized, another growth mechanism of the nanocrystals was found to occur, driven by the reduction of the total grain boundary energy.

We report on the fabrication of magnetite/salicylic acid/silica shell/antibiotics (Fe3O4/SA/SiO2/ATB) thin films by matrix-assisted pulsed laser evaporation (MAPLE) to inert substrates. Fe3O4-based powder have been synthesized and investigated by XRD and TEM. All thin films were studied by FTIR, SEM and in vitro biological assays using Staphylococcus aureus and Pseudomonas aeruginosa reference strains, as well as eukaryotic HEp-2 cells. The influence of the obtained nanosystems on the microbial biofilm development as well as their biocompatibility has been assessed. For optimum deposition conditions, we obtained uniform adherent films with the composition identical with the raw materials. Fe3O4/SA/SiO2/ATB thin films had an inhibitory activity on the ability of microbial strains to initiate and develop mature biofilms, in a strain-and antibiotic-dependent manner. These magnetite silica thin films are promising candidates for the development of novel materials designed for the inhibition of medical biofilms formed by different pathogenic agents on common substrates, frequently implicated in the etiology of chronic and hard to treat infections.

The doping process of LiF with Pb has been described by using structural ab initio modeling and experimental results. The values of formation energy of several complexes involving Pb ions show that the presence of charge-balancing vacancies ease the metal incorporation in the crystal. The metal successively captures the vacancies to form a final stable complex Pb-Li(center dot) + V-Li('). Experimental data from X-ray absorption spectroscopy confirm the presence of Pb in LiF crystals in this site revealing both Pb-F bonds and collinear Pb-F-Li atomic configurations. A maximum solubility of Pb in LiF of the order of 3 x 10(20)/cm(3) can be estimated from these calculations. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4793751]

The surface structure, interface reactivity, electron configuration and magnetic properties of Sm layers deposited on Si(0 0 1) at various temperatures are investigated by low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS) and magneto-optical Kerr effect (MOKE). It is found that metal Sm is present on samples prepared at low temperature, with an interface layer containing SmSi2 and Sm4Si3. When samples are prepared at high temperature, much less metal Sm is found, with an increasing amount of SmSi2. Room temperature ferromagnetism is observed for all prepared layers, with a decrease of the saturation magnetization when samples are prepared at high temperature. It is found that ferromagnetism implies mostly a compound with approximate stoichiometry Sm4Si3. Also, the decrease in the intensity of the XAS 2p(3/2) -> 3d white lines with the corresponding increasing amount of SmSi2 may be explained by assuming a higher occupancy of Sm 5d orbitals (5d(2) configuration), most probably due to hybridation effects. (C) 2012 Elsevier B. V. All rights reserved.

Cotton fabrics were coated with arrays of ZnO hexagonal prisms using an electroless (catalytic/auto-catalytic) deposition process. A typical three step method, similar to those used for electroless deposition of metals on insulating substrates, consisting of pre-activation, activation and deposition steps was employed. The low-dimensional ZnO particles were grown from an aqueous solution containing zinc nitrate as source of zinc ions and dimethylamineborane as reducing agent. The as-obtained ZnO-coated cotton fabrics were characterized from the point of view of structure by X-ray diffraction (XRD) and morphology by scanning electron microscopy (SEM). The XRD studies demonstrate that the ZnO particles have a hexagonal wurtzite crystalline structure. The SEM observations prove that the cotton fibers are homogeneously covered by hexagonal prisms which have uniform base size of approximately 500 nm and height of 1 mu m. Optical spectroscopy measurements show that the functionalization with ZnO strongly decreases the transmittance in the UV vis region of the cotton fabrics. An important characteristic is that the ZnO-functionalized cotton fabrics exhibit superhydrophobicity, with water contact angles exceeding 150 degrees. The technique described is highly reproducible, easy scalable and cheap, allowing a wide range of applications. (C) 2012 Elsevier B.V. All rights reserved.

Highly textured ZnO thin films were implanted with Co ions at fluences of 1 x 10(16) and 1 x 10(17) ions cm(-2). Although their microstructure observed by analytical high-resolution electron microscopy was very different, SQUID magnetometer measurements showed qualitatively similar magnetic properties. In the low-fluence film, only small modifications, such as a slight amorphization, planar defects or very small (<1-1.5 nm) Co clusters, were hardly observable. Implantation at a higher fluence led to important changes in the film structure: heavy amorphization and metallic Co precipitates were identified by electron diffraction, energy dispersive x-ray spectroscopy (EDS), electron energy loss spectroscopy and scanning transmission electron microscopy spectrum imaging. EDS microanalysis additionally revealed the presence of similar to 2 at% Co atoms that were likely dissolved in the ZnO lattice at the atomic level. No Co oxides or other secondary oxide phases were detected. For both implanted samples, the dimensions of Co precipitates were below the superparamagnetic limit at room temperature. Thermo-magnetization curves and magnetic hysteresis loops measured in the temperature range from 5 to 300 K indicated two superimposed magnetic regimes, one predominant above 50 K and the other below 50 K. We analysed the possible mechanisms and quantitative contributions to explain the observed magnetic behaviour at low and room temperature.

A simple approach to fabricate periodic arrays of ring bumps, disk and convex bumps or holes on silicon and gallium arsenide substrates is reported. In the process, a mono or double layer of 700 nm diameter silica colloidal particles were self-assembled on the substrates and a single pulse from a 200 fs laser at 387 nm wavelength was applied. The surfaces were irradiated at normal incidence by immersing the substrates in a glass container filled with acetone, carbon tetrachloride and 1,1,2-trichlor-trifluorethan liquid precursors. The influence of the medium on the near-field interactions for both substrates is investigated. (C) 2012 Elsevier B.V. All rights reserved.

The influence of different TiO2 precursors (laboratory-prepared sol-gel powders, dried and thermally treated at 400 degrees C, and commercial powders such as anatase by Aldrich and P25 Aeroxide by Evonik) on the structure and morphology of the titanate nanotubes obtained by hydrothermal method was investigated by x-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. In all cases, titanate-based nanotubes were obtained, having similar structure and morphology. The effect of the thermal treatment on the structural stability was also studied by differential thermal analysis and thermogravimetry analysis (TG/DTA) and differetial scanning calorimetry (DSC) measurements up to 600 degrees C, to determine the transformation of titanate nanotubes into other phases. Complementarily, by XRD investigation, the phases that develop after the thermal treatment of the titanate nanotubes in 110-400 degrees C temperature range were identified. The TEM micrographs come to confirm the deterioration of morphology and transformation from nanotubes to particles. The thermal stability of the investigated nanotubes led to the conclusion that this property depends not only on the sodium content but also on the type of precursor. The highest thermal stability was noticed for the nanotubes synthesized starting with anatase (Aldrich) commercial powder.