Structure of Extremely Nanosized and Confined In-O Species in Ordered Porous Materials

Perturbed-angular correlation, x-ray absorption, and small-angle x-ray scattering spectroscopies were suitably combined to elucidate the local structure of highly diluted and dispersed InOx species confined in porous of ZSM5 zeolite. These novel approach allow us to determined the structure of extremely nanosized In-O species exchanged inside the 10-atom-ring channel of the zeolite, and to quantify the amount of In2O3 crystallites deposited onto the external zeolite surface.Comment: 4 pages, 5 postscript figures, REVTEX4, published in Physical Review Letter

Cationic exchange in nanosized ZnFe2O4 spinel revealed by experimental and simulated near-edge absorption structure

The non-equilibrium cation site occupancy in nanosized zinc ferrites (6-13 nm) with different degree of inversion (0.2 to 0.4) was investigated using Fe and Zn K-edge x-ray absorption spectroscopy XANES and EXAFS, and magnetic measurements. The very good agreement between experimental and ab-initio calculations on the Zn K-edge XANES region clearly show the large Zn2+(A)--Zn2+[B] transference that takes place in addition to the well-identified Fe3+[B]--Fe3+(A) one, without altering the long-range structural order. XANES spectra features as a function of the spinel inversion were shown to depend on the configuration of the ligand shells surrounding the absorbing atom. This XANES approach provides a direct way to sense cationic inversion in these spinel compounds. We also demonstrated that a mechanical crystallization takes place on nanocrystalline spinel that causes an increase of both grain and magnetic sizes and, simultaneously, generates a significant augment of the inversion.Comment: 5 pages, 5 eps figures, uses revtex4, corrected table

Spontaneous oxidation of disordered fcc FePt nanoparticles

In this work we present new results on spontaneous oxidation of disordered fcc FePt nanoparticles. The "as-made" oleic acid and oleylamine coated FePt nanoparticles of average size 4 nm synthesized by a high-boiling coordinating solvent method were exposed to air over a period of days and characterized structurally and magnetically by means of different techniques such as XANES, XPS, EXAFS, and SQUID magnetometry. The "as-made" FePt nanoparticles stabilize in the disordered fcc structure and have a very low magnetic saturation (M(s)=11 emu/g) and a huge coercive field (H_(c)=1800 Oe) compared to the low temperature bulk values of the disordered fcc FePt. We observed that the coercive field and the magnetic saturation change with the time the sample is exposed to air and these changes are associated with the oxidation or passivation of the nanoparticle surface that gives place to a core-shell structure. Indeed, the study on the electronic properties of the nanoparticles confirms the magnetic results and indicates that when the nanoparticles are exposed to air, changes in the oxidation state of both Fe and Pt occur, the oxidation state of Fe coming close to hematite. The formation of hematite tends to soften the "as-made" FePt nanoparticles as observed by the reduction of the coercive field to almost one third of the original value. Although the hematite softens the FePt nanoparticles, there is an exchange coupling at the interface of the core-shell characterized by the increase of the coercive field from 300 to 900 Oe when the sample is cooled in an applied field of 50 kOe

Stability and Reversible Oxidation of Sub-Nanometric Cu5 Metal Clusters: Integrated Experimental Study and Theoretical Modeling

12 pags., 6 figs.Sub-nanometer Metal clusters have special physical and chemical properties, significantly different from those of nanoparticles. However, there is a major concern about their thermal stability and susceptibility to oxidation. In situ X-ray Absorption spectroscopy and Near Ambient Pressure X-ray Photoelectron spectroscopy results reveal that supported Cu5 clusters are resistant to irreversible oxidation at least up to 773 K, even in the presence of 0.15 mbar of oxygen. These experimental findings can be formally described by a theoretical model which combines dispersion-corrected DFT and first principles thermochemistry revealing that most of the adsorbed O2 molecules are transformed into superoxo and peroxo species by an interplay of collective charge transfer within the network of Cu atoms and large amplitude "breathing" motions. A chemical phase diagram for Cu oxidation state of the Cu5-oxygen system is presented, clearly different from the already known bulk and nano-structured chemistry of Cu.This work has been partly supported by the Spanish Ministerio de Ciencia e Innovación (TED2021-131899BI00/MCIN/AEI/10.13039/501100011033/ Unión Europea NextGenerationEU/PRTR), and the Agencia Estatal de Investigación (AEI) and the Fondo Europeo de Desarrollo Regional (FEDER, UE) under Grants Nos, PID2019-107115GBC21, and PID2020-117605GB-I00; the EU Doctoral Network PHYMOL 101073474 (project call reference HORIZON-MSCA2021-DN-01); the Austrian Science Fund (FWF) under Grant P29893-N36; XUNTA DE GALICIA (Spain) (Grupos Ref. Comp. 2021 - ED431C 2021/16); ANPCyT PICT (2017-1220 and 2017- 3944) and UNLP (Project 11/X937), Argentina. This publication is also based upon work of COST Action CA21101 "Confined molecular systems: from a new generation of materials to the stars" (COSY) supported by COST (European Cooperation in Science and Technology).Peer reviewe

Role of age and comorbidities in mortality of patients with infective endocarditis

Purpose: The aim of this study was to analyse the characteristics of patients with IE in three groups of age and to assess the ability of age and the Charlson Comorbidity Index (CCI) to predict mortality. Methods: Prospective cohort study of all patients with IE included in the GAMES Spanish database between 2008 and 2015. Patients were stratified into three age groups:<65 years, 65 to 80 years, and = 80 years.The area under the receiver-operating characteristic (AUROC) curve was calculated to quantify the diagnostic accuracy of the CCI to predict mortality risk. Results: A total of 3120 patients with IE (1327 < 65 years;1291 65-80 years;502 = 80 years) were enrolled.Fever and heart failure were the most common presentations of IE, with no differences among age groups.Patients =80 years who underwent surgery were significantly lower compared with other age groups (14.3%, 65 years; 20.5%, 65-79 years; 31.3%, =80 years). In-hospital mortality was lower in the <65-year group (20.3%, <65 years;30.1%, 65-79 years;34.7%, =80 years;p < 0.001) as well as 1-year mortality (3.2%, <65 years; 5.5%, 65-80 years;7.6%, =80 years; p = 0.003).Independent predictors of mortality were age = 80 years (hazard ratio [HR]:2.78;95% confidence interval [CI]:2.32–3.34), CCI = 3 (HR:1.62; 95% CI:1.39–1.88), and non-performed surgery (HR:1.64;95% CI:11.16–1.58).When the three age groups were compared, the AUROC curve for CCI was significantly larger for patients aged <65 years(p < 0.001) for both in-hospital and 1-year mortality. Conclusion: There were no differences in the clinical presentation of IE between the groups. Age = 80 years, high comorbidity (measured by CCI), and non-performance of surgery were independent predictors of mortality in patients with IE.CCI could help to identify those patients with IE and surgical indication who present a lower risk of in-hospital and 1-year mortality after surgery, especially in the <65-year group

Role of age and comorbidities in mortality of patients with infective endocarditis

[Purpose]: The aim of this study was to analyse the characteristics of patients with IE in three groups of age and to assess the ability of age and the Charlson Comorbidity Index (CCI) to predict mortality. [Methods]: Prospective cohort study of all patients with IE included in the GAMES Spanish database between 2008 and 2015.Patients were stratified into three age groups:<65 years,65 to 80 years,and ≥ 80 years.The area under the receiver-operating characteristic (AUROC) curve was calculated to quantify the diagnostic accuracy of the CCI to predict mortality risk. [Results]: A total of 3120 patients with IE (1327 < 65 years;1291 65-80 years;502 ≥ 80 years) were enrolled.Fever and heart failure were the most common presentations of IE, with no differences among age groups.Patients ≥80 years who underwent surgery were significantly lower compared with other age groups (14.3%,65 years; 20.5%,65-79 years; 31.3%,≥80 years). In-hospital mortality was lower in the <65-year group (20.3%,<65 years;30.1%,65-79 years;34.7%,≥80 years;p < 0.001) as well as 1-year mortality (3.2%, <65 years; 5.5%, 65-80 years;7.6%,≥80 years; p = 0.003).Independent predictors of mortality were age ≥ 80 years (hazard ratio [HR]:2.78;95% confidence interval [CI]:2.32–3.34), CCI ≥ 3 (HR:1.62; 95% CI:1.39–1.88),and non-performed surgery (HR:1.64;95% CI:11.16–1.58).When the three age groups were compared,the AUROC curve for CCI was significantly larger for patients aged <65 years(p < 0.001) for both in-hospital and 1-year mortality. [Conclusion]: There were no differences in the clinical presentation of IE between the groups. Age ≥ 80 years, high comorbidity (measured by CCI),and non-performance of surgery were independent predictors of mortality in patients with IE.CCI could help to identify those patients with IE and surgical indication who present a lower risk of in-hospital and 1-year mortality after surgery, especially in the <65-year group

Complementary methods for cluster size distribution measurements: supported platinum nanoclusters in methane reforming catalysts

Pt cluster size strongly influences the reactivity of surfaces for C-H bond activation during CH4 steam reforming. C-H bond activation turnover rates for H2O reforming of CH4 increased with decreasing Pt cluster size, suggesting that coordinatively unsaturated surface Pt atoms are more reactive than Pt atoms in low-index surfaces prevalent in larger clusters. Near-edge fine structure in X-ray absorption spectra clearly shows electronic changes in Pt clusters relative to bulk Pt crystallites, though differences in the 5d electronic density among samples with different cluster size could not be related directly to Pt surface atom coordination. These results suggest that catalytic consequences of cluster size arise from surface structure changes leading to coordinative unsaturation of surface atoms. X-ray absorption and small angle X-ray scattering techniques were used to measure the size of Pt metal nanoclusters and the results are compared with H-2 chemisorption and transmission electron microscopy data. (C) 2004 Elsevier B.V. All rights reserved

Improved kinetic behaviour of Mg(NH2)2-2LiH doped with nanostructured K-modified-LixTiyOz for hydrogen storage

The system Mg(NH2)2 + 2LiH is considered as an interesting solid-state hydrogen storage material owing to its low thermodynamic stability of ca. 40 kJ/mol H2 and high gravimetric hydrogen capacity of 5.6 wt.%. However, high kinetic barriers lead to slow absorption/desorption rates even at relatively high temperatures (>180 °C). In this work, we investigate the effects of the addition of K-modified LixTiyOz on the absorption/desorption behaviour of the Mg(NH2)2 + 2LiH system. In comparison with the pristine Mg(NH2)2 + 2LiH, the system containing a tiny amount of nanostructured K-modified LixTiyOz shows enhanced absorption/desorption behaviour. The doped material presents a sensibly reduced (∼30 °C) desorption onset temperature, notably shorter hydrogen absorption/desorption times and reversible hydrogen capacity of about 3 wt.% H2 upon cycling. Studies on the absorption/desorption processes and micro/nanostructural characterizations of the Mg(NH2)2 + 2LiH + K-modified LixTiyOz system hint to the fact that the presence of in situ formed nanostructure K2TiO3 is the main responsible for the observed improved kinetic behaviour