Institute Of Recerca En Energia Of Catalonia Irec

Barcelona, Spain

Institute Of Recerca En Energia Of Catalonia Irec

Barcelona, Spain
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Carvalho D.L.,Military Institute of Engineering of Rio de Janeiro | Borges L.E.P.,Military Institute of Engineering of Rio de Janeiro | Appel L.G.,Brazilian National Institute of Technology | Ramirez De La Piscina P.,University of Barcelona | And 2 more authors.
Catalysis Today | Year: 2013

The interaction of ethanol and its evolution to n-butanol over different MgAl mixed oxides derived from hydrotalcite precursors is studied by FTIR and in situ DRIFT-MS experiments. The evolution of different surface species is monitored as a function of thermal treatments. Acetaldehyde appears as a primary intermediate which converts over the mixed oxides to C4 products through the aldol condensation reaction. However, acetaldehyde also produces surface carboxylate species which compete for the active sites and make the condensation process less efficient. © 2013 Elsevier B.V. All rights reserved.

Prades J.D.,EME | Prades J.D.,Institute Of Recerca En Energia Of Catalonia Irec | Jimenez-Diaz R.,EME | Hernandez-Ramirez F.,EME | And 5 more authors.
Sensors and Actuators, B: Chemical | Year: 2010

A fully autonomous and fast chemical gas sensor system is presented. This proof-of-concept device is based on the exploitation of the dissipated power at individual nanowires by Joule effect induced by the bias current applied in conductometric measurements (self-heating), which enables heating the tiny mass of these wires up to the optimum temperature for gas sensing applications with power values as low as a few tens of μW. Here, this interesting feature is exploited to develop a sensor system that only requires few mW to bias, heat and measure the response of the sensing material. This power value can be supplied by state-of-the-art energy harvesting technologies, such as thermoelectric microgenerators. We also demonstrate that using a single nanowire reduces the thermal inertia of the sensors, minimizes gas diffusion processes, and results in fast dynamic responses only limited by the surface reaction kinetics. For all these reasons, the here-presented system is an important step forward towards fully autonomous and distributed gas sensor networks based on ultra-fast devices without the need of battery replacement. © 2009 Elsevier B.V. All rights reserved.

Epifani M.,CNR Institute of Neuroscience | Arbiol J.,Catalan Institution for Research and Advanced Studies | Pellicer E.,University of Barcelona | Sergent N.,French National Center for Scientific Research | And 3 more authors.
Materials Chemistry and Physics | Year: 2010

The decomposition of metal (Ti, Zr, Sn) alkoxides at 250 °C in a solution of tetradecene and dodecylamine resulted in the formation of ultra-small (1-2 nm) oxide nanoparticles. The nanoparticles showed unusual structural properties. The high-pressure orthorhombic phase was found for SnO2. The as-synthesized ZrO2 nanoparticles were only partially crystallized. It was possible to observe their in situ crystallization under the TEM beam. The TiO2 nanoparticles appeared amorphous, with only a few nanocrystals dispersed in the sample. The temperature evolution of the samples was investigated in situ by Raman spectroscopy. All SnO2 was converted to stable cassiterite at 350 °C. TiO2 and ZrO 2 samples displayed phase stability reversal over a broad range of temperatures. © 2010 Elsevier B.V. All rights reserved.

Prades J.D.,University of Barcelona | Hernandez-Ramirez F.,University of Barcelona | Hernandez-Ramirez F.,Institute Of Recerca En Energia Of Catalonia Irec | Fischer T.,University of Cologne | And 6 more authors.
Applied Physics Letters | Year: 2010

Self-heating effect in individual metal oxide nanowires can be used to activate their response to gases with power consumptions below tenths of microwatts. The thermal response time of these devices is extremely fast (a few milliseconds) and it makes it possible to observe the kinetics of the interactions between the gas molecules and the metal oxide. In this work we demonstrate that such effects enable an experimental methodology to improve the selectivity of metal oxide-based sensors based on the analysis of their fast response dynamics. Specifically, this work jointly analyzes the magnitude and response time of SnO2 nanowire-based sensors to carbon monoxide (CO) and humidity (H2 O) mixtures, proving that a quantitative analysis of CO- H2 O gas blends can be achieved by modulating their work temperature through the self-heating effect. © 2010 American Institute of Physics.

Echavarria A.P.,University of Lleida | Torras C.,Institute Of Recerca En Energia Of Catalonia Irec | Pagan J.,University of Lleida | Ibarz A.,University of Lleida
Food Engineering Reviews | Year: 2011

This article provides an overview of recent developments and the published literature in membrane technology with regard to fruit juice processing and considers the impact of such technology on product quality. In the fruit juice industry, membrane technology is used mainly to clarify the juice by means of ultrafiltration and microfiltration and to concentrate it by means of nanofiltration and reverse osmosis. We look at enzyme immobilization techniques to improve filtration performance and operation methods to quantify fouling. Membrane fouling is a critical issue and inhibits the broader application of membranes in the fruit production industry. Pectin and its derivatives form a gel-like structure over the membrane surface, thereby reducing the permeate flux. In order to degrade pectin, the raw juice is usually subjected to an enzymatic treatment with pectinase, which hydrolyses pectin and causes its protein complexes to flocculate. The resulting juice has reduced viscosity and a much lower pectin content, which is advantageous in the subsequent filtration processes. © 2011 Springer Science + Business Media, LLC.

Hernandez-Ramirez F.,Institute Of Recerca En Energia Of Catalonia Irec | Hernandez-Ramirez F.,University of Barcelona | Prades J.D.,University of Barcelona | Hackner A.,Airbus | And 5 more authors.
Nanoscale | Year: 2011

Gas detection experiments were performed with individual tin dioxide (SnO2) nanowires specifically configured to observe surface ion (SI) emission response towards representative analyte species. These devices were found to work at much lower temperatures (T ≈ 280°C) and bias voltages (V ≈ 2 V) than their micro-counterparts, thereby demonstrating the inherent potential of individual nanostructures in building functional nanodevices. High selectivity of our miniaturized sensors emerges from the dissimilar sensing mechanisms of those typical of standard resistive-type sensors (RES). Therefore, by employing this detection principle (SI) together with RES measurements, better selectivity than that observed in standard metal oxide sensors could be demonstrated. Simplicity and specificity of the gas detection as well as low-power consumption make these single nanowire devices promising technological alternatives to overcome the major drawbacks of solid-state sensor technologies. © 2011 The Royal Society of Chemistry.

Hertog W.,Institute Of Recerca En Energia Of Catalonia Irec | Llenas A.,Institute Of Recerca En Energia Of Catalonia Irec | Carreras J.,Institute Of Recerca En Energia Of Catalonia Irec
Optics Express | Year: 2015

This article demonstrates the benefits of complementing a daylight-lit environment with a spectrally tunable illumination system. The spectral components of daylight present in the room are measured by a lowcost miniature spectrophotometer and processed through a number of optimization algorithms, carefully trading color fidelity for energy efficiency. Spectrally-tunable luminaires provide only those wavelengths that ensure that either the final illumination spectrum inside the room is kept constant or carefully follows the dynamic spectral pattern of natural daylight. Analyzing the measured data proves that such a hybrid illumination system brings both unprecendented illumination quality and significant energy savings. © 2015 Optical Society of America.

Epifani M.,National Research Council Italy | Arbiol J.,Catalan Institution for Research and Advanced Studies | Andreu T.,University of Barcelona | Andreu T.,Institute Of Recerca En Energia Of Catalonia Irec | And 2 more authors.
Crystal Growth and Design | Year: 2010

Metal ferrite (MFe2O4, with M = Fe, Mn, Co, Ni, Cu, Zn) nanoparticles were synthesized by processing metal oxide sols in a coordinating environment. The sols were prepared by forced hydrolysis of the starting metal nitrates, in the presence of acetylacetone for avoiding precipitation. Two different processing routes were investigated. In the first, the sol was injected into a hot (160 °C) solution of dodecylamine in tetradecene. In the second route the injection environment was constituted by pure dodecylamine heated at the same temperature. The precipitate from the first route was heat-treated in air at various temperatures, from 200 to 500 °C. The redispersible nanoparticles from the second route were annealed in oleylamine at temperatures up to 220 °C. In the first case, crystallization was obtained only after heat-treatment at 500 °C, while 220 °C was sufficient for crystallizing the nanoparticles dispersed in oleylamine. The samples from the two routes were investigated by X-ray diffraction and transmission electron microscopy/electron energy loss spectroscopy in the case system of NiFe2O4. The product from the first route, after heating at 200 °C, was a disordered material, with a broad size distribution of aggregates and Ni depletion regions. The product from the second route was constituted by discrete nanoparticles with the correct cation stoichiometry. The interpretation of the results allowed concluding that obtaining simple structural reorganization in nanosized volumes is a key factor for crystallization under mild conditions. © 2010 American Chemical Society.

Reparaz J.S.,TU Berlin | Guell F.,University of Barcelona | Wagner M.R.,TU Berlin | Callsen G.,TU Berlin | And 5 more authors.
Applied Physics Letters | Year: 2010

In this work, we investigate the influence of finite size on the recombinations dynamics of ZnO nanowires. We demonstrate that diameter as well as length of nanowires determine the lifetime of the neutral donor bound excitons. Our findings suggest that while the length is mainly responsible for different mode quality factors of the cavity-like nanowires, the diameter determines the influence of surface states as alternative recombinations channels for the optical modes trapped in the nanocavity. In addition, comparing nanowires grown using different catalyst we show that the surfaces states strongly depend on each precursor characteristics. © 2010 American Institute of Physics.

Epifani M.,CNR Institute for Microelectronics and Microsystems | Andreu T.,University of Barcelona | Andreu T.,Institute Of Recerca En Energia Of Catalonia Irec | Zamani R.,Institute Of Recerca En Energia Of Catalonia Irec | And 8 more authors.
CrystEngComm | Year: 2012

TiO2 nanocrystals were prepared by solvothermal treatment in oleic acid at 250 °C of amorphous TiO2 nanoparticles. The latter were prepared by sol-gel processing in dodecylamine at 100 °C of starting solutions synthesized from TiCl4. For preparing Pt/TiO2 nanocomposites, with Pt/Ti nominal atomic ratio of 0.05, the required amount of Pt precursor was added to the amorphous TiO2 nanoparticles before heating at 250 °C. Control synthesis experiments, evaluated by X-ray diffraction and X-ray photoelectron spectroscopy showed Pt(acac)2 as the best Pt precursor, and 250 °C as the optimum temperature for simultaneous TiO2 crystallization and efficient Pt nucleation. Transmission electron microscopy observations evidenced Pt nanocrystals dispersed in the surrounding TiO2 host, with a mean size of 4 nm. The TiO2 host was constituted of rod-shaped anatase nanocrystals. Comparison with pure TiO2 showed that the rod shape was favored by the presence of Pt species. As an example of application, the nanocomposites were used for preparing ethanol-sensing devices. The Pt addition remarkably improved the response with respect to pure TiO2 sensors, and electrical characterization of the sensors helped in establishing that the effect of Pt was due to spillover rather than electronic sensitization. © 2012 The Royal Society of Chemistry.

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