Scientific Papers in SCI

2013


Title: Impact of Ce–Fe synergism on the catalytic behaviour of Au/CeO2–FeOx/Al2O3 for pure H2 production
Author(s): Reina, TR; Ivanova, S; Idakiev, V; Delgado, JJ; Ivanov, I; Tabakova, T; Centeno, MA; Odriozola, JA
Source: Catalysis Science & Technology, 3 (2013) 779-787

abstract | fulltext

In this work the development of a series of gold catalysts, essentially based on γ-alumina promoted with a small superficial fraction of Ce–Fe mixed oxides, is reported. The catalytic behaviour is evaluated in the water gas shift reaction. The formation of a Ce–Fe solid solution is evidenced by XRD and related to the catalytic activity where the importance of the Ce–Fe interaction is demonstrated. The best catalyst reached CO conversions very close to the equilibrium limit. A long-term stability test is performed and the loss of activity is observed and attributed to reaction intermediates. Almost complete recovery of the initial conversion is achieved after oxidation treatment, suggesting that the problem of stability could be overcome by a suitable change in the reaction parameters thus leading to a highly efficient catalyst for future applications in H2 production and clean-up.

March, 2013 | DOI: 10.1039/C2CY20537H

Title: A Novel 3D Architecture of GdPO4 Nanophosphors: Multicolored and White Light Emission
Author(s): Becerro, AI; Rodriguez-Liviano, S; Fernandez-Carrion, AJ; Ocaña, M
Source: Crystal Growth & Design, 55 (2013) 454-460

abstract | fulltext

Homogeneous monoclinic GdPO4 particles composed of three intersecting lance-shaped crystals forming a penetration twin have been synthesized following a very restrictive, simple, and fast (10 min) method consisting of the hydrothermal reaction of gadolinium acetylacetonate with H3PO4 in a mixture of ethylene glycol and water at 180 °C. Slightly increasing the amount of water in the solvent mixture leads to hexagonal rodlike GdPO4·0.5H2O nanoparticles, whereas the variation of the Gd source, PO4 source, aging temperature, and polyol type gave rise to heterogeneous particles. The synthesis procedure is also suitable for the preparation of Eu3+-, Tb3+-, and Dy3+-doped GdPO4 particles with the same morphology and crystalline structure as the undoped materials. The effect of the doping level on the luminescent properties of the twinlike nanophosphors was evaluated, finding optimum doping levels of 5, 5, and 1% for the Eu3+-, Tb3+-, and Dy3+-doped materials, respectively. The twinlike GdPO4 nanophosphors were found to be more efficient than the rodlike GdPO4 ones in terms of emission intensity. Finally, a solid-state single-phase white-light-emitting nanophosphor has been fabricated for the first time in this system by triply doping the GdPO4 twined particles with appropriate concentrations of Eu3+, Tb3+, and Dy3+ and exciting through the Gd–Ln energy-transfer band at 273 nm. In addition to this energy transfer band, other energy charge transfer processes among the three dopants (Eu3+, Tb3+, and Dy3+) have been observed in the triply doped material.

February, 2013 | DOI: 10.1021/cg301023k

Title: Microwave-Assisted Synthesis of Biocompatible Europium-Doped Calcium Hydroxyapatite and Fluoroapatite Luminescent Nanospindles Functionalized with Poly(acrylic acid)
Author(s): Escudero, A; Calvo, ME; Rivera-Fernandez, S; de la Fuente, JM; Ocana, M
Source: Langmuir, 29 (2013)

abstract | fulltext

Europium-doped calcium hydroxyapatite and fluoroapatite nanophosphors functionalized with poly(acrylic acid) (PAA) have been synthesized through a one-pot microwave-assisted hydrothermal method from aqueous basic solutions containing calcium nitrate, sodium phosphate monobasic, and PAA, as well as sodium fluoride in the case of the fluoroapatite particles. In both cases a spindlelike morphology was obtained, resulting from an aggregation process of smaller subunits which also gave rise to high specific surface area. The size of the nanospindles was 191 (32) × 40 (5) nm for calcium hydroxyapatite and 152 (24) × 38 (6) nm for calcium fluoroapatite. The luminescent nanoparticles showed the typical red luminescence of Eu3+, which was more efficient for the fluoroapatite particles than for the hydroxyapatite. This is attributed to the presence of OH– quenchers in the latter. The nanophosphors showed negligible toxicity for Vero cells. Both PAA-functionalized nanophosphors showed a very high (up to at least 1 week) colloidal stability in 2-(N-morpholino)ethanesulfonic acid (MES) at pH 6.5, which is a commonly used buffer for physiological pH. All these features make both kinds of apatite-based nanoparticles promising tools for biomedical applications, such as luminescent biolabels and tracking devices in drug delivery systems.

February, 2013 | DOI: 10.1021/la304534f

Title: Ionic Liquid Mediated Synthesis and Surface Modification of Multifunctional Mesoporous Eu:GdF3 Nanoparticles for Biomedical Applications
Author(s): Rodriguez-Liviano, S; Nunez, NO; Rivera-Fernandez, S; de la Fuente, JM; Ocana, M
Source: Langmuir, 29 (2013) 3411-3418

abstract | fulltext

A procedure for the synthesis of multifunctional europium(III)-doped gadolinium(III) fluoride (Eu:GdF3) nanoparticles (85 nm) with quasispherical shape by precipitation at 120 °C from diethylene glycol solutions containing lanthanide chlorides and an ionic liquid (1-Butyl, 2-methylimidazolium tetrafluoroborate) as fluoride source has been developed. These nanoparticles were polycrystalline and crystallized into a hexagonal structure, which is unusual for GdF3. They were also mesoporous (pore size = 3.5 Å), having a rather high BET surface area (75 m2 g–1). The luminescent and magnetic (relaxivity) properties of the Eu:GdF3 nanoparticles have been also evaluated in order to assess their potentiality as “in vitro” optical biolabels and contrast agent for magnetic resonance imaging. Finally, a procedure for their functionalization with aspartic-dextran polymers is also reported. The functionalized Eu:GdF3 nanoparticles presented negligible toxicity for Vero cells, which make them suitable for biotecnological applications.

March, 2013 | DOI: 10.1021/la4001076

Title: Arsenic sorption by nanocrystalline magnetite: An example of environmentally promising interface with geosphere
Author(s): Bujnakova, Z; Balaz, P; Zorkovska, A; Sayagues, MJ; Kovac, J; Timko, M
Source: Journal of Hazardous Materials, 262 (2013) 1204-1212

abstract | fulltext

In this paper, the sorption of arsenic onto nanocrystalline magnetite mineral Fe3O4 was studied in a model system. Nanocrystalline magnetite was produced by mechanical activation in a planetary ball mill from natural microcrystalline magnetite. As a consequence of milling, the specific surface area increased from 0.1 m2/g to 11.9 m2/g and the surface site concentration enhanced from 2.2 sites/nm2 to 8.4 sites/nm2. These changes in surface properties of magnetite lead to the enhancement of arsenic removal from model system. The best sorption ability was achieved with magnetite sample activated for 90 min. In this case the sample was able to absorb around 4 mg/g. The structural changes of magnetite were also observed and the new hematite phase was detected after 120 min of milling. A good correlation between the decreasing particle size, increasing specific surface area and reduction of saturation magnetization was found. In desorption study, KOH and NaOH were found as the best eluents where more than 70% of arsenic was released back into the solution. The principal novelty of the paper is that mineral magnetite, truly one nature's gift can be used after “smart” milling (mechanical activation) as an effective arsenic sorbent.

November, 2013 | DOI: 10.1016/j.jhazmat.2013.03.007

Title: CO2 multicyclic capture of pretreated/doped CaO in the Ca-looping process. Theory and experiments
Author(s): Valverde, JM; Sanchez-Jimenez, PE; Perejon, A; Perez-Maqueda, LA
Source: Physical Chemistry Chemical Physics, 15 (2013) 11775-11793

abstract | fulltext

We study in this paper the conversion of CaO-based CO2 sorbents when subjected to repeated carbonation–calcination cycles with a focus on thermally pretreated/doped sorbents. Analytical equations are derived to describe the evolution of conversion with the cycle number from a unifying model based on the balance between surface area loss due to sintering in the looping-calcination stage and surface area regeneration as a consequence of solid-state diffusion during the looping-carbonation stage. Multicyclic CaO conversion is governed by the evolution of surface area loss/regeneration that strongly depends on the initial state of the pore skeleton. In the case of thermally pretreated sorbents, the initial pore skeleton is highly sintered and regeneration is relevant, whereas for nonpretreated sorbents the initial pore skeleton is soft and regeneration is negligible. Experimental results are obtained for sorbents subjected to a preheating controlled rate thermal analysis (CRTA) program. By applying this preheating program in a CO2 enriched atmosphere, CaO can be subjected to a rapid carbonation followed by a slow rate controlled decarbonation, which yields a highly sintered skeleton displaying a small conversion in the first cycle and self-reactivation in the next ones. Conversely, carbonation of the sorbent at a slow controlled rate enhances CO2 solid-state diffusion, which gives rise, after a quick decarbonation, to a highly porous skeleton. In this case, CaO conversion in the first cycle is very large but it decays abruptly in subsequent cycles. Data for CaO conversion retrieved from the literature and from further experimental measurements performed in our work are analyzed as influenced by a variety of experimental variables such as preheating temperature program, preheating exposition time, atmosphere composition, presence of additives, and carbonation–calcination conditions. Conversion data are well fitted by the proposed model equations, which are of help for a quantitative interpretation of the effect of experimental conditions on the multicyclic sorbent performance as a function of sintering/regeneration parameters inferred from the fittings and allow foreseeing the critical conditions to promote reactivation. The peculiar behavior of some pretreated sorbents, showing a maximum conversion in a small number of cycles, is explained in light of the model.

July, 2013 | DOI: 10.1039/C3CP50480H

Title: Spectroscopic properties of electrochemically populated electronic states in nanostructured TiO2 films: anatase versus rutile
Author(s): Berger, T; Anta, JA; Morales-Florez, V
Source: Physical Chemistry Chemical Physics, 15 (2013) 13790-13795

abstract | fulltext

A thorough characterization of nanostructured materials under application-relevant conditions is a prerequisite for elucidating the interplay between their physicochemical nature and their functional properties in practical applications. Here, we use a spectroelectrochemical approach to study the population of electronic states in different types of nanostructured anatase and rutile TiO2 films in contact with an aqueous electrolyte. The spectroscopic properties of the two polymorphs were addressed under Fermi level control in the energy range between the fundamental absorption threshold and the onset of lattice absorption (3.3–0.1 eV). The results evidence the establishment of an equilibrium between localized Ti3+ centers absorbing in the vis/NIR and shallow (e−)(H+) traps absorbing in the MIR upon electron accumulation in anatase electrodes. The absence of the MIR-active (e−)(H+) traps on all rutile electrodes points to a crystal structure-dependent electron population in the films.

September, 2013 | DOI: 10.1039/C3CP52324A

Title: Gold(III) stabilized over ionic liquids grafted on MCM-41 for highly efficient three-component coupling reactions
Author(s): Bobadilla, LF; Blasco, T; Odriozola, JA
Source: Physical Chemistry Chemical Physics, 39 (2013) 16927-16934

abstract | fulltext

Two alkoxysilyl-modified ionic liquids (ILs) have been synthesized and further grafted onto mesoporous silica, MCM-41; these ionic liquids were used for dispersing AuCl3 catalysts that activate C–H bonds as required for the synthesis of propargylamines by coupling alkyne, aldehyde and amine (A3 coupling) species. 29Si NMR experiments demonstrate the formation of covalent bonds between alkoxysilyl-modified Bmim IL and the MCM-41 surface through silanol groups. The catalytic activities of Au(III)-supported MCM-41 and Au(III) homogeneous catalysts are lower than those obtained for the IL functionalized Au–MCM-41 solids when the same gold loading is considered. An interaction between Au(III) species and the IL is proposed for explaining the stabilization of gold(III) species. However, successive reaction cycles result in a decrease in the catalytic activity that has been explained on the basis of gold leaching.

October, 2013 | DOI: 10.1039/C3CP52924J

Title: Surface modified Eu:GdVO4 nanocrystals for optical and MRI imaging
Author(s): Nunez, Nuria O.; Rivera, Sara; Alcantara, David; de la Fuente, Jesus M.; Garcia-Sevillano, Jorge; Ocana, Manuel
Source: Dalton Transactions, 42 (2013) 10725-10734

abstract | fulltext

A facile solvothermal route has been developed for the preparation of europium doped gadolinium orthovanadate nanoparticles ([similar]70 nm) with tetragonal structure, based on a homogenous precipitation reaction at 120 °C from rare earth precursors (yttrium nitrate and europium nitrate) and sodium orthovanadate solutions using an ethylene glycol–water mixture as the solvent. The effects of the doping level on the luminescence properties were evaluated in order to find the optimum nanophosphors. These nanocrystals were successfully functionalized with amino (two step process) and carboxylate (one-pot process) groups provided by amino-dextran polymers (AMD) and polyacrylic acid (PAA), respectively. It was found that while the luminescent properties of both kinds of functionalized systems were similar, the colloidal stability of the PAA-modified sample was higher, because of which, it was selected to study their cytotoxicity and magnetic properties (relaxivity and phantom analyses) to assess their potentiality as multifunctional probes for both “in vitro” optical biolabels and negative contrast agents for magnetic resonance imaging.

August, 2013 | DOI: 10.1039/C3DT50676B

Title: Spark plasma sintering of TixTa1−xC0.5N0.5-based cermets: Effects of processing conditions on chemistry, microstructure and mechanical properties
Author(s): Cordoba, Jose M.; Chicardi, Ernesto; Poyato, Rosalia; Gotor, Francisco J.; Medri, Valentina; Guicciardi, Stefano; Melandri, Cesare
Source: Chemical Engineering Journal, 230 (2013) 558-566

abstract | fulltext

Nanometric powdered TixTa1−xC0.5N0.5-based cermets were fabricated using a mechanically induced self-sustaining reaction and consolidated by spark plasma sintering. Highly dense cermets were obtained, and their chemistry, microstructure and mechanical properties were characterised by X-ray diffraction, scanning electron microscopy, image analysis, microindentation and nanoindentation. The microhardness was found to depend directly on the contiguity and size of the ceramic hard particles. The samples synthesised at the lowest temperature (1150 °C) exhibited more homogeneous microstructures and smaller ceramic particles and the best combination of microhardness and fracture toughness.

August, 2013 | DOI: 10.1016/j.cej.2013.06.104

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