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Arzac G.M.,University of Seville | Rojas T.C.,University of Seville | Gontard L.C.,University of Seville | Chinchilla L.E.,University of Cadiz | And 4 more authors.
RSC Advances

In our previous works, Co-B-O and Co-Ru-B-O ultrafine powders with variable Ru content (xRu) were studied as catalysts for hydrogen generation through sodium borohydride hydrolysis. These materials have shown a complex nanostructure in which small Co-Ru metallic nanoparticles are embedded in an amorphous matrix formed by Co-Ru-B-O based phases and B2O3. Catalytic activity was correlated to nanostructure, surface and bulk composition. However, some questions related to these materials remain unanswered and are studied in this work. Aspects such as: 3D morphology, metal nanoparticle size, chemical and electronic information on the nanoscale (composition and oxidation states), and the study of the formation or not of a CoxRu1-x alloy or solid solution are investigated and discussed using XAS (X-ray Absorption Spectroscopy) and Scanning Transmission Electron Microscopy (STEM) techniques. Also magnetic behavior of the series is studied for the first time and the structure-performance relationships discussed. All Co-containing samples exhibited ferromagnetic behavior up to room temperature while the Ru-B-O sample is diamagnetic. For the xRu = 0.13 sample, an enhancement in the Hc (coercitive field) and Ms (saturation magnetization) is produced with respect to the monometallic Co-B-O material. However this effect is not observed for samples with higher Ru content. The presence of the CoxB-rich (cobalt boride) amorphous ferromagnetic matrix, very small metal nanoparticles (Co and CoxRu(1-x)) embedded in the matrix, and the antiferromagnetic CoO phase (for the higher Ru content sample, xRu = 0.7), explain the magnetic behavior of the series. © the Partner Organisations 2014. Source

Otal E.H.,Laboratory for Materials Science and Technology | Otal E.H.,CONICET | Kim M.L.,Laboratory for Materials Science and Technology | Kim M.L.,CONICET | And 5 more authors.
Chemical Communications

The optical absorption of UiO-66-NH2 MOF was red-shifted using a diazo-coupling reaction. The modifications performed with naphthols and aniline yielded reddish samples, and the modifications with diphenylaniline yielded dark violet ones. The photocatalytic activity of these modified MOFs was assessed for methylene blue degradation, showing a good performance relative to traditional TiO2. The degradation performance was found to correlate with the red shift of the absorption edge. These findings suggest potential applications of these materials in photocatalysis and in dye sensitized solar cells. © The Royal Society of Chemistry. Source

Fabregas I.O.,CONICET | Reinoso M.,CONICET | Reinoso M.,Comision Nacional de la Energia Atomica | Reinoso M.,National University of San Martin of Argentina | And 4 more authors.
Journal of the European Ceramic Society

Zirconia-based materials are widely investigated and used as electrolytes in solid-oxide fuel cells, oxygen sensors and electrochemical devices. These materials present polymorphism, which has a critical effect on their technologically important properties. The polymorphism is influenced by, among other factors, aliovalent dopant nature and content, grain size and interfacial energy.In this work, we investigated the crystal structure of ZrO2-12mol% CaO and -9mol% Y2O3 dense ceramics as a function of grain size. We found that the samples undergo a phase transition from the t″ form of the tetragonal phase to the cubic phase with an increase in grain size. This transition is directly detected by Raman spectroscopy and further evidence is given by a change in the activation energy for bulk ionic conduction. The transition occurs at an average grain size greater than 500nm for both systems. © 2016 Elsevier Ltd. Source

Otal E.H.,CONICET | Otal E.H.,Laboratory for Materials Science and Technology | Sileo E.,University of Buenos Aires | Aguirre M.H.,University of Zaragoza | And 3 more authors.
Journal of Alloys and Compounds

Lanthanide doped ZnO are interesting materials for optical and electrical applications. The wide band gap of this semiconductor makes it transparent in the visible range (Egap = 3.2 eV), allowing a sharp emission from intra shell transition from the lanthanides. From the electrical side, ZnO is a widely used material in varistors and its electrical properties can be tailored by the inclusion of lanthanides. Both applications are influenced by the location of the lanthanides, grain boundaries or lattice inclusion. Yb doped ZnO samples obtained by wet chemistry route were annealed at different temperatures and characterized by Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), Rietveld refinement of XRD data, and X-ray Absorption Fine Structure (XAFS). These techniques allowed to follow the changes occurred in the matrix and the Yb environment. The use of the Cauchy continuous wavelet transform allowed identifying a second coordination shell composed of Zn atoms, supporting the observations from XRD Rietveld refinement and XAFS fittings. The information obtained confirmed the incorporation of Yb in Oh sites of the wurtzite structure without Yb2O3 clustering in the lattice. © 2014 Elsevier B.V. Source

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