Scientific Papers in SCI

2013


Title: Liquids Analysis with Optofluidic Bragg Microcavities
Author(s): Oliva-Ramirez, M; Gonzalez-Garcia, L; Parra-Barranco, J; Yubero, F; Barranco, A; Gonzalez-Elipe, AR
Source: ACS Applied Materials & Interfaces, 5 (2013) 6743-650

abstract | fulltext

Porous Bragg microcavities formed by stacking a series of porous nanocolumnar layers with alternate low (SiO2) and high (TiO2) refractive index materials have been prepared by physical vapor deposition at glancing angles (GLAD). By strictly controlling the porosity and refractive index of the individual films, as well as the relative orientation of the nanocolumns from one layer to the next, very porous and nondispersive high optical quality microcavities have been manufactured. These photonic structures have been implemented into responsive devices to characterize liquids, mixtures of liquids, or solutions flowing through them. The large displacements observed in the optical spectral features (Bragg reflector gap and resonant peak) of the photonic structures have been quantitatively correlated by optical modeling with the refractive index of the circulating liquids. Experiments carried out with different glucose and NaCl solutions and mixtures of water plus glycerol illustrate the potentialities of these materials to serve as optofluidic devices to determine the concentration of solutions or the proportion of two phases in a liquid mixture.

July, 2013 | DOI: 10.1021/am401685r

Title: Preferential oxidation of CO in excess H2 over CuO/CeO2 catalysts: Characterization and performance as a function of the exposed face present in the CeO2 support
Author(s): Gamarra, D; Camara, AL; Monte, M; Rasmussen, SB; Chinchilla, LE; Hungria, AB; Munuera, G; Gyorffy, N; Schay, Z; Corberan, VC; Conesa, JC; Martinez-Arias, A
Source: Applied Catalysis B: Environmental, 130-131 (2013) 224-238

abstract | fulltext

A series of oxidised copper-cerium nanostructured catalysts prepared by impregnation of copper over ceria supports synthesized by different methods (hydrothermal with varying preparation parameters, microemulsion/precipitation), in order to achieve different specific morphologies (nanocubes, nanorods and nanospheres), have been examined with respect to their catalytic properties for preferential oxidation of CO in excess H2 (CO-PROX). The catalysts have been characterized in detail by XRD, Raman, SBET measurement, HREM, XPS, TPR and EPR, which allows establishing a model of structural characteristics of the catalysts. The characterization results have been correlated with analysis of CO-PROX catalytic properties by means of catalytic activity measurements complemented by operando-DRIFTS. Structural dependence of the CO oxidation reaction on the dispersed copper oxide entities as a function of the exposed face present at the surface of the different ceria supports is revealed. An important overall enhancement of the CO-PROX performance is detected for the sample supported on ceria nanocubes which is proposed to be a consequence of the interaction between copper oxide and (1 0 0) faces of the ceria support.

February, 2013 | DOI: 10.1016/j.apcatb.2012.11.008

Title: Multiple Zeolite Structures from One Ionic Liquid Template
Author(s): Blanes, JMM; Szyja, BM; Romero-Sarria, F; Centeno, MA; Hensen, EJM; Odriozola, JA; Ivanova, S
Source: Chemistry-A European Journal, 19 (2013) 2122-2130

abstract | fulltext

This study reports the use of 1-butyl-3-methyl imidazolium methanesulfonate ionic liquid as a template in the synthesis of zeolites. It is found that the silicon source determines the formation of beta (BEA), mordenite framework inverted (MFI), or analcime (ANA) zeolites. Depending on this source, different preorganized complexes are obtained that drive the formation of the different zeolite structures. In the presence of ethanol, the ionic liquid form preorganized complexes that drive the formation of MFI. In its absence, BEA is obtained. Whereas, the large amount of sodium present when using sodium metasilicate leads to ANA formation. A molecular simulation study of the relative stability of the template-framework system and location of the template provides further insight into the mechanism of synthesis.

February, 2013 | DOI: 10.1002/chem.201202556

Title: Constant rate thermal analysis for enhancing the long-term CO2 capture of CaO at Ca-looping conditions
Author(s): Valverde, JM; Sanchez-Jimenez, PE; Perejon, A; Perez-Maqueda, LA
Source: Applied Energy, 108 (2013) 108-120

abstract | fulltext

Experimental results are reported on the (Ca-looping) multicyclic CO2 capture of CaO and nanosilica/CaO composites derived from Ca(OH)2 and nanosilica/Ca(OH)2 dry mixtures subjected in situ to linear and constant rate thermal analysis (CRTA) preheating programs in either air or air/CO2 atmospheres. By means of CRTA preheating the rates of the reactions taking place during pretreatment are kept at a constant and small value along the entire process. In agreement with a pore skeleton model, previously proposed in the literature for explaining the behavior of natural limestones thermally pretreated, our results suggest that air/CO2-CRTA pretreatment yields a thermally stable hard skeleton of poorly reactive CaO on which a soft skeleton of reactive CaO would be supported. The sorbent subjected to this preheating program exhibits a reactivation in the very first carbonation/calcination cycles, after which CaO conversion decays slowly with the cycle number. In contrast, linearly or air-CRTA preheated sorbents show a significant decrease of CaO conversion within the first cycles. In the latter case, CaO multicyclic conversion fits well to a model where it is assumed that the progressive reduction of surface area as the number of carbonation/calcination cycles is increased obeys to sintering of the preheated sorbent skeleton as it is subjected to repeated calcinations during cycling. In the former case, CaO conversion data conforms to the prediction by a model in which the loss of surface area is mainly due to sintering of a nascent CaO soft skeleton regenerated in the diffusive carbonation phase, which is enhanced by the air/CO2-CRTA pretreatment. As regards the effect of nanosilica, the results indicate that it slows down CaO sintering during pretreatment, which hinders the development of a stable CaO skeleton thus hampering reactivation and stabilization of conversion. On the other hand, as CaO sintering is also lessened during looping calcination, nanosilica is useful to increase the absolute values of CaO conversion.

August, 2013 | DOI: 10.1016/j.apenergy.2013.03.013

Title: Colored and Transparent Oxide Thin Films Prepared by Magnetron Sputtering: The Glass Blower Approach
Author(s): Gil-Rostra, J; Chaboy, J; Yubero, F; Vilajoana, A; Gonzalez-Elipe, AR
Source: ACS Applied Materials & Interfaces, 5 (2013) 1967-1976

abstract | fulltext

This work describes the reactive magnetron sputtering processing at room temperature of several mixed oxide MxSiyOz thin films (M: Fe, Ni, Co, Mo, W, Cu) intended for optical, coloring, and aesthetic applications. Specific colors can be selected by adjusting the plasma gas composition and the Si–M ratio in the magnetron target. The microstructure and chemistry of the films are characterized by a large variety of techniques including X-ray photoemission spectroscopy, X-ray absorption spectroscopy (XAS), and infrared spectroscopy, while their optical properties are characterized by UV–vis transmission and reflection analysis. Particularly, XAS analysis of the M cations in the amorphous thin films has provided valuable information about their chemical state and local structure. It is concluded that the M cations are randomly distributed within the SiO2 matrix and that both the M concentration and its chemical state are the key parameters to control the final color of the films.

March, 2013 | DOI: 10.1021/am302778h

Title: Solution Properties of the System ZrSiO4–HfSiO4: A Computational and Experimental Study
Author(s): Cota, Agustin; Burton, Benjamin P.; Chain, Pablo; Pavon, Esperanza; Alba, Maria D.
Source: Journal of Physical Chemistry C, 117 (2013) 10013-10019

abstract | fulltext

ZrSiO4 and HfSiO4 are of considerable interest because of their low thermal expansions, thermal conductivities, and the optical properties of HfSiO4. In addition, silicate phases of both are studied as model radioactive waste disposal materials. Previous first principles calculations reported near ideal mixing in the Zr1–xHfxSiO4 system, with a very weak propensity for phase separation. Density functional theory (DFT)/cluster-expansion first principles calculations presented in this work indicate near ideal mixing with a very weak propensity for ordering. Zr1–xHfxSiO4 samples (x = 0, 0.25, 0.5, 0.75, and 1.0) were synthesized from intimate stoichiometric mixtures of constituent-oxides and annealing at 1823 K for 20 days in a platinum crucible. Samples were characterized by X-ray diffraction (XRD; Rietveld analysis) and 29Si MAS NMR. The XRD data exhibited a pronounced negative deviation from Vegard’s law in the excess volume of mixing, and the 29Si MAS NMR spectra also suggest nonideal mixing. Given the very weak energetics that favor cation ordering, it is clear that there must be some other cause(s) for the observed deviations from ideal mixing behavior.

May, 2013 | DOI: 10.1021/jp401539g

Title: Crystal Structures and Photoluminescence across the La2Si2O7–Ho2Si2O7 System
Author(s): Fernandez-Carrion, AJ; Allix, M; Ocana, M; Garcia-Sevillano, J; Cusso, F; Fitch, AN; Suard, E; Becerro, AI
Source: Inorganic Chemistry, 52 (2013) 13469-13479

abstract | fulltext

The La2Si2O7−Ho2Si2O7 system displays a solid solubility region of G-(La,Ho)2Si2O7 which extends to the La0.6Ho1.4Si2O7 composition. Compositions richer in Ho3+ show a two-phase domain (G+δ), while δ-(La,Ho)2Si2O7 is the stable phase for Ho3+ contents higher than La0.2Ho1.8Si2O7. A preferential occupation of Ho for the RE2 site of the G-unit cell is observed. Luminescence measurements have shown that the lifetimes remain unchanged in the range 0.5% < [Ho3+] < 10%, and only above this value does concentration quenching become operative.

November, 2013 | DOI: 10.1021/ic401867c

Title: Monoclinic–Tetragonal Heterostructured BiVO4 by Yttrium Doping with Improved Photocatalytic Activity
Author(s): Usai, S; Obregon, S; Becerro, AI; Colon, G
Source: Journal of Physical Chemistry C, 117 (2013) 24479-24484

abstract | fulltext

Yttrium-doped BiVO4 has been synthesized by means of a surfactant free hydrothermal method having good photoactivities under sun-like excitation for the degradation of Methylene Blue (MB). From the structural and morphological characterization it has been stated that the presence of Y3+ induces the progressive stabilization of the tetragonal phase and the slight higher surface area values. By following the tetragonal cell parameters, the substitutional incorporation of Y3+ into the BiVO4 tetragonal lattice might be considered. Best photocatalytic performances were attained for the samples with Y3+ content of 3.0 at. % for which the MB degradation rate constant appears 2-fold higher. Furthermore, photoactivities for visible-light-driven O2 evolution demonstrate that the photocatalytic performance of the best Y-doped system (initial rate of O2 evolution, 285 μmol g–1 h–1) was more than 5 times that of undoped m-BiVO4 (initial rate of O2 evolution, 53 μmol g–1 h–1). The occurrence of Y3+ doping and a monoclinic–tetragonal heterostructured BiVO4 system induces the higher photocatalytic activities. PL analysis provides a clear evidence of the lower charge carriers recombination in heterostructured yttrium-doped systems.

October, 2013 | DOI: 10.1021/jp409170y

Title: Synthesis and Properties of Multifunctional Tetragonal Eu:GdPO4 Nanocubes for Optical and Magnetic Resonance Imaging Applications
Author(s): Rodriguez-Liviano, S; Becerro, AI; Alcantara, D; Grazu, V; de la Fuente, JM; Ocana, M
Source: Inorganic Chemistry, 52 (2013) 647-654

abstract | fulltext

A simple and fast (7 min) procedure for synthesis of gadolinium phosphate nanocubes (edge = 75 nm) based on the microwave-assisted heating at 120 °C of gadolinium acetylacetonate and phosphoric acid solutions in buthylene glycol is reported. These nanocubes were highly crystalline and crystallized into a tetragonal structure, which has not been ever reported for pure gadolinium phosphate. Determination of such crystal structure has been carried out here for the first time in the literature by means of powder X-ray diffraction. The developed synthesis procedure was also successful for preparation of multifunctional europium(III)-doped the gadolinium phosphate nanocubes, which were nontoxic for cells and exhibited strong red luminescence under UV illumination and high transverse relaxivity (r2) values. These properties confer them potential applications as biolabels for in vitro optical imaging and as negative contrast agent for magnetic resonance imaging.

January, 2013 | DOI: 10.1021/ic3016996

Title: Crystal Structure and Luminescent Properties of Eu3+-Doped A-La2Si2O7 Tetragonal Phase Stabilized by Spray Pyrolysis Synthesis
Author(s): Fernandez-Carrion, Alberto J.; Ocana, Manuel; Florian, Pierre; Garcia-Sevillano, Jorge; Cantelar, Eugenio; Fitch, Andrew N.; Suchomel, Matthew R.; Becerro, Ana I.
Source: Journal of Physical Chemistry C, 117 (2013) 20876-20886

abstract | fulltext

Pure A-La2Si2O7 powder has been synthesized through a spray pyrolysis method followed by calcination at 1100 degrees C for 15 h. The crystallographic structure, refined from the synchrotron powder diffraction pattern of the sample, showed tetragonal symmetry with space group P4(1), a = 6.83565(1) angstrom, and c = 24.84133(1) angstrom. The Si-29 and La-139 NMR spectra have been described here for the first time in the literature and could be simulated with four Si and four La resonances, respectively, in good agreement with the presence of four Si and four La crystallographic sites in the unit cell. The same synthesis method was 2 successful for the synthesis of Eu3+-doped A-La2Si2O7 (%Eu = 3-40). The analysis of the unit cell volumes indicated that Eu3+ replaces La3+ in the unit cell for all Eu3+ substitution levels investigated. However, anomalous diffraction data indicated that the La/Eu substitution mechanism was not homogeneous, but Eu much prefers to occupy the RE3 sites. The Eu-doped A-La2Si2O7 phosphors thus synthesized exhibited a strong orange-red luminescence after excitation at 393 nm. Lifetime measurements indicated that the optimum phosphor was that with an Eu3+ content of 20%, which showed a lifetime of 2.3 ms. The quantum yield of the latter was found to be 12% at 393 nm excitation. These experimental observations together with the high purity of the phase obtained by the proposed spray pyrolysis method make this material an excellent phosphor for optoelectronic applications.

October, 2013 | DOI: 10.1021/jp407172z

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