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142 results on '"Beltrán-Mir, Héctor"'

8. Non-Stoichiometric Ba x Mn 0.7 Cu 0.3 O 3 Perovskites as Catalysts for CO Oxidation: Optimizing the Ba Content.

Author

Díaz-Verde, Álvaro, dos Santos Veiga, Emerson Luiz, Beltrán-Mir, Héctor, Illán-Gómez, María José, and Cordoncillo-Cordoncillo, Eloísa

Subjects
OXYGEN vacancy, COPPER oxidation, SPARK ignition engines, WASTE gases, ELECTRIC conductivity, COPPER
Abstract

In this work, a series of BaxMn0.7Cu0.3O3 samples (x: 1, 0.9, 0.8, and 0.7, BxMC) was synthesized, characterized, and used as catalysts for CO oxidation reaction. All formulations were active for CO oxidation in the tested conditions. A correlation between the electrical conductivity, obtained by impedance spectroscopy, and the reducibility of the samples, obtained by H2-TPR, was observed. The Ba0.8Mn0.7Cu0.3O3 composition (B0.8MC) showed the best catalytic performance (comparable to that of the 1% Pt/Al2O3 reference sample) during tests conducted under conditions similar to those found in the exhaust gases of current gasoline engines. The characterization data suggest the simultaneous presence of a high Mn(IV)/Mn(III) surface ratio, oxygen vacancies, and reduced copper species, these two latter being key properties for ensuring a high CO conversion percentage as both are active sites for CO oxidation. The reaction temperature and the reactant atmosphere composition seem to be the most important factors for achieving a good catalytic performance, as they strongly determine the location and stability of the reduced copper species. [ABSTRACT FROM AUTHOR]

Published
2025
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24. Impedance spectroscopy: A useful technique to unveil the mechanism of a CO oxidation reaction.

Author

dos Santos Veiga, Emerson Luiz, Beltrán‐Mir, Héctor, Vendrell, Xavier, Llorca, Jordi, and Cordoncillo, Eloísa

Subjects
*IMPEDANCE spectroscopy, *MIXED oxide catalysts, *GAS-solid interfaces, *REACTIVE oxygen species
Abstract

In this work, the impedance spectroscopy (IS) technique was used to aid in understanding the reaction mechanism of the CO oxidation reaction using the Pr2Zr2−xFexO7±δ (x = 0 and 0.10) mixed oxide as a heterogeneous catalyst. The catalytic reaction occurred in the same temperature range where there was a decrease in the overall resistivity of the materials. Moreover, it has been observed that within the temperature range where the catalytic process takes place, there is a variation in the A and n parameters of the power law dispersion. Combining IS with catalytic reactions offers a robust approach to enhance the understanding of the mechanisms involved in the CO oxidation reaction. It enables precise analysis of the changes that take place at the solid–gas interface, particularly the generation of reactive oxygen species. Furthermore, it allows examining the relationship between the presence of oxygen vacancies and defects, which directly impact the catalytic process. [ABSTRACT FROM AUTHOR]

Published
2024
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30. Kinetics or thermodynamics? Extolling their role to modulate the crystal phases and luminescence of KY3F10:Eu3+ powders.

Author

Serna-Gallén, Pablo, Beltrán-Mir, Héctor, and Cordoncillo, Eloísa

Subjects
*THERMODYNAMICS, *THERMODYNAMIC control, *CRYSTALS, *LUMINESCENCE, *TIME-resolved spectroscopy
Abstract

KY3F10, a fluoride compound with two polymorphs (α and δ), has been a subject of study due to its unique properties. Obtaining the metastable δ-phase has been challenging, but this study presents an enhanced synthetic methodology using coprecipitation to isolate specific crystal phases. Varying the reaction temperature and time allows for the modulation of polymorph formation. The structural analysis of the synthesized powders reveals the influence of kinetic and thermodynamic control. The morphology of the particles is also affected by these factors, with different reaction conditions leading to distinct particle shapes. The luminescent response of Eu3+-doped powders helps understand the structural stability. It is demonstrated that time-resolved fluorescence spectroscopy is a sensitive and direct measurement to follow the observed changes. Overall, this study demonstrates the interplay between thermodynamics and kinetics in materials synthesis and the impact on crystal phase formation and properties. [ABSTRACT FROM AUTHOR]

Published
2023
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33. The catalytic activity of the Pr2Zr2−xFexO7±δsystem for theCO oxidation reaction

Author

Monteiro dos Santos, Emerson Francis, Vendrell , Xavier, Llorca, Jordi, Beltrán Mir, Héctor, and Cordoncillo, Eloisa

Subjects
pyrochlore, heterogeneous catalysis, oxidation state, praseodymium and iron, CO oxidation reaction
Abstract

One of the alternatives to decrease the concentration of CO is its oxidation reaction to CO2, which can be made more efficient using catalysts. In this work, it is shown that pyrochlore structures are a promising candidate to act as heterogeneous catalysts due to their chemical and physical properties. For use as a catalyst in this reaction, the Pr2Zr2−xFexO7±δ (x = 0, 0.05, 0.10, and 0.15) system was synthesized by the solvothermal method, firing the powder obtained at temperatures of 1200 and 1400°C. The diffraction patterns confirmed the pyrochlore structure as the single phase in all the nominal compositions. The Brunauer–Emmett–Teller method and dynamic light-scattering analysis showed an increase in the particle size and a decrease in the specific surface area when increasing the iron concentration and increasing the calcination temperature. The compositions that presented the best catalytic activity were the samples with the highest iron concentration. Moreover, these samples were able to convert all the CO oxidation reactions in a narrower temperature range than a conventional CeO2 sample. The presence of vacancies and the redox behavior of the elements present are the key factors for the catalysis of this system in the CO oxidation reaction. Funding for open access charge: CRUE-Universitat Jaume I

Published
2022

35. Site-selective symmetries of Eu3+-doped BaTiO3 ceramics: a structural elucidation by optical spectroscopy

Author

Universidad Jaime I, Ministerio de Economía y Competitividad (España), Ministerio de Ciencia, Innovación y Universidades (España), Eusko Jaurlaritza, Universidad del País Vasco, European Commission, Serna-Gallén, Pablo [0000-0002-1471-5344], Beltrán-Mir, Héctor [0000-0002-7836-1602], Cordoncillo, Eloísa [0000-0002-9368-1815], Balda, Rolindes [0000-0001-6882-3167], Fernández, Joaquín [0000-0003-4673-167X], Serna-Gallén, Pablo, Beltrán-Mir, Héctor, Cordoncillo, Eloísa, West, Anthony R., Balda, Rolindes, Fernández, Joaquín, Universidad Jaime I, Ministerio de Economía y Competitividad (España), Ministerio de Ciencia, Innovación y Universidades (España), Eusko Jaurlaritza, Universidad del País Vasco, European Commission, Serna-Gallén, Pablo [0000-0002-1471-5344], Beltrán-Mir, Héctor [0000-0002-7836-1602], Cordoncillo, Eloísa [0000-0002-9368-1815], Balda, Rolindes [0000-0001-6882-3167], Fernández, Joaquín [0000-0003-4673-167X], Serna-Gallén, Pablo, Beltrán-Mir, Héctor, Cordoncillo, Eloísa, West, Anthony R., Balda, Rolindes, and Fernández, Joaquín

Abstract

Eu-Doped BaTiO ceramics with dopant contents between 0 and 10 mol% were prepared by sol-gel synthesis based on the nominal compositions (BaEu)TiO and Ba(TiEu)O, where two possible substitution mechanisms are addressed. By means of optical spectroscopy, our study gives a plausible elucidation of Eu site occupation in micron-sized BaTiO particles. Time-resolved fluorescence line narrowing (TRFLN) shows the presence of five different crystal field sites for europium ions and possible symmetries are inferred for each one. The solubility limit of the lanthanide ion was found to be about 3 mol%. The experimental results are consistent with the preference of Eu to occupy Ba sites regardless of the nominal compositions and target substitution mechanism. However, TRFLN results showed that the dopant could also occupy Ti sites, highlighting the amphoteric character of Eu. The existence of anti-Stokes and Stokes vibronic sidebands in the D → F transitions of Eu ions is confirmed. This can explain the lack of resolution found in room temperature spectra of these transitions due to vibronic mixing of the excited levels. The existence of non-equivalent europium sites with different spectroscopic properties could have an impact on the optical properties of doped-BaTiO ceramics and associated applications.

Published
2019

37. Toward Expanding the Optical Response of Ag2CrO4 and Bi2O3 by Their Laser-Mediated Heterojunction

Author

Torres-Mendieta, Rafael Omar, primary, Teixeira, Mayara Mondego, additional, Mínguez-Vega, Gladys, additional, de Souza, Daniele, additional, Gobato, Yara Galvão, additional, Assis, Marcelo, additional, Beltrán-Mir, Héctor, additional, Cordoncillo, Eloisa, additional, Andrés, Juan, additional, Černík, Miroslav, additional, and Longo, Elson, additional

Published
2020
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38. α‑AgVO3 Decorated by Hydroxyapatite (Ca10(PO4)6(OH)2): Tuning Its Photoluminescence Emissions and Bactericidal Activity

Author

da Silva, Jussara Soares, Machado, Thales Rafael, Martins, Tiago A., Assis, Marcelo de, Foggi, Camila Cristina, Guerra Macedo, Nadia, Beltrán Mir, Héctor, Cordoncillo, Eloisa, Andres, Juan, and Longo, Elson

Subjects
bactericidal, hydroxyapatite, photoluminescence, α-silver vanadate
Abstract

Defect-related luminescent materials have attracted interest because of their excellent optical properties and are considered as a less expensive and nontoxic alternative to commonly used lanthanide-based optical systems. These materials are fundamentally and technologically important for the next generation of full-color tunable light-emitting diodes as well as in the biomedical field. In this study, we report the preparation of α-silver vanadate (α-AgVO3, AV) decorated by hydroxyapatite (Ca10(PO4)6(OH)2, HA) with intense photoluminescence (PL) emissions at various HA/AV molar ratios (1:1–1:1/32) by a simple route based on chemical precipitation. The well-defined diffraction peaks observed by X-ray diffraction were all indexed to the monoclinic AV and hexagonal HA phases. Analysis of the results obtained by Fourier transform infrared spectroscopy reveals the presence of short-range structural order as deduced by the characteristic vibrational modes assigned to AV and HA systems. Characterization by scanning and transmission electron microscopies confirms the presence of AV and HA micro- and nanorods, respectively. UV–vis spectroscopy renders band gap energies of 5.80 eV for HA and in the range 2.59–2.65 eV for pure AV and HA/AV samples. The PL data reveal the presence of broad-band emission profiles, typical of defect-related optical centers in materials. Depending on the molar ratio, the emission can be completely tunable from the blue to red spectral regions; in addition, pure white color emission was obtained. On the basis of these results, we propose an order–disorder model induced by structural and interface defects to explain the PL emissions in the HA/AV system. Moreover, our results show that HA/AV composites have superior bactericidal activity against Staphylococcus aureus (methicillin-resistant and methicillin-susceptible) and can be used as a novel multifunctional material.

Published
2019

41. Tailoring the Bactericidal Activity of Ag Nanoparticles/α-Ag2WO4 Composite Induced by Electron Beam and Femtosecond Laser Irradiation: Integration of Experiment and Computational Modeling

Author

Macedo, Nadia G., primary, Machado, Thales R., additional, Roca, Roman A., additional, Assis, Marcelo, additional, Foggi, Camila Cristina, additional, Puerto-Belda, Verónica, additional, Mínguez-Vega, Gladys, additional, Rodrigues, André, additional, San-Miguel, Miguel A., additional, Cordoncillo, Eloisa, additional, Beltrán-Mir, Héctor, additional, Andrés, Juan, additional, and Longo, Elson, additional

Published
2019
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44. From Complex Inorganic Oxides to Ag–Bi Nanoalloy: Synthesis by Femtosecond Laser Irradiation

Author

Machado, Thales R., primary, Macedo, Nadia G., additional, Assis, Marcelo, additional, Doñate-Buendia, Carlos, additional, Mínguez-Vega, Gladys, additional, Teixeira, Mayara M., additional, Foggi, Camila C., additional, Vergani, Carlos E., additional, Beltrán-Mir, Héctor, additional, Andrés, Juan, additional, Cordoncillo, Eloisa, additional, and Longo, Elson, additional

Published
2018
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45. A TEACHING STRATEGY TO UNDERSTAND THE SOLID STATE CHEMISTRY FOR HIGH LEVEL EDUCATION STUDENTS: AN EXPERIENCE WITH A PHOSPHORESCENCE MATERIAL

Author

Stilbyte, Viktorija, primary, Peña-Huguet, Iván, additional, Pérez-Maseda, Marta, additional, Mollar-Cuni, Andrés, additional, Gutiérrez-Blanco, María, additional, Rueda, Celia M., additional, Serna-Gallen, Pablo, additional, Fortuño-Morte, María, additional, Beltrán-Mir, Héctor, additional, and Cordoncillo, Eloisa, additional

Published
2018
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46. A new series of environment-friendly reddish inorganic pigments based on AFeO3(A = Ln, Y) with high NIR solar reflectance

Author

Fortuño-Morte, Maria, Serna-Gallén, Pablo, Beltrán-Mir, Héctor, and Cordoncillo, Eloísa

Abstract

Environment-friendly pigments based on AFeO3(A = La, Pr, Nd, Sm, Gd, Tb, Y or Yb) with high near-infrared (NIR) reflectance were synthesised by a coprecipitation method at 1200 °C. The Rietveld refinement analysis showed single-phase orthorhombic perovskite for all compositions. All pigments, which showed reddish hues, offered good colour stability after mixing these pigments in powder form with siloxane transparent paint and two different glazes. The powder–paint mixtures produced with GdFeO3, TbFeO3and YFeO3pigments have the highest NIR solar reflectance, reaching values of R = 50%. The temperature shielding studies conducted using TbFeO3pigment–paint mixture for a roof coating yielded a reduction of 3.2 °C in comparison to a commercial pigment. Moreover, the glazes that were pigmented using GdFeO3, TbFeO3and YFeO3compositions also presented the most intense reddish colours. A study of the thermal and chemical stability of the pigment with the highest NIR solar reflectance showed good stability in both cases. The reddish pigments that were prepared can therefore be good candidates for use in different applications such as cool pigments or pigments for ceramic glazes at high temperatures.

Published
2021
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47. Towards the scale-up of the formation of nanoparticles on α-Ag2WO4 with bactericidal properties by femtosecond laser irradiation

Author

Assis, Marcelo, primary, Cordoncillo, Eloisa, additional, Torres-Mendieta, Rafael, additional, Beltrán-Mir, Héctor, additional, Mínguez-Vega, Gladys, additional, Oliveira, Regiane, additional, Leite, Edson R., additional, Foggi, Camila C., additional, Vergani, Carlos E., additional, Longo, Elson, additional, and Andrés, Juan, additional

Published
2018
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48. Laser-induced formation of bismuth nanoparticles

Author

Assis, Marcelo, primary, Cordoncillo, Eloísa, additional, Torres-Mendieta, Rafael, additional, Beltrán-Mir, Héctor, additional, Mínguez-Vega, Gladys, additional, Gouveia, Amanda Fernandes, additional, Leite, Edson, additional, Andrés, Juan, additional, and Longo, Elson, additional

Published
2018
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50. Toward Expanding the Optical Response of Ag2CrO4and Bi2O3by Their Laser-Mediated Heterojunction

Author

Torres-Mendieta, Rafael Omar, Teixeira, Mayara Mondego, Mínguez-Vega, Gladys, de Souza, Daniele, Gobato, Yara Galvão, Assis, Marcelo, Beltrán-Mir, Héctor, Cordoncillo, Eloisa, Andrés, Juan, Černík, Miroslav, and Longo, Elson

Abstract

The formation of heterojunctions between semiconductors with distinct properties usually expands their capabilities. In this context, many methodologies have been employed in pursuing efficient and fruitful heterojunctions. However, poor attention has been paid to the employment of photonics-based strategies, which lately demonstrated to have great potential for the structural modification of semiconductors. In the current work, we report the laser-mediated generation of heterojunctions between Ag2CrO4and Bi2O3, two semiconductors with contrasting properties. The products were prepared by the laser irradiation of different semiconductor’s mixture ratios and further analyzed using various electron- and photon-based characterization techniques, different from mechanical grinding, which is considered the most straightforward way to obtain heterojunctions. The laser’s intense optical field prompted not only the formation of tight and uniform junctions between the composing semiconductors but also induced Ag and Bi nanoparticles’ production on their surfaces. This resulted in a modulation of the optical band gap to the narrowest value found in the semiconductor components and low recombination of the photoinduced charge carriers regardless of the amount ratio of the composing semiconductors. Therefore, this work will be of great importance for the creation of materials with a potential exploitability in the light-powered sectors.

Published
2020
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