Person: Torralvo Fernández, María Josefa
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First Name
María Josefa
Last Name
Torralvo Fernández
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Químicas
Department
Química Inorgánica
Area
Química Inorgánica
Identifiers
6 results
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Now showing 1 - 6 of 6
Item Mesoporous Silica Matrix as a Tool for Minimizing Dipolar Interactions in NiFe2O4 and ZnFe2O4 Nanoparticles(Nanomaterials, 2017) Virumbrales del Olmo, Maider; Sáez Puche, Regino; Torralvo Fernández, María Josefa; Blanco Gutiérrez, VerónicaNiFe2O4 and ZnFe2O4 nanoparticles have been prepared encased in the MCM (Mobile Composition of Matter) type matrix. Their magnetic behavior has been studied and compared with that corresponding to particles of the same composition and of a similar size (prepared and embedded in amorphous silica or as bare particles). This study has allowed elucidation of the role exerted by the matrix and interparticle interactions in the magnetic behavior of each ferrite system. Thus, very different superparamagnetic behavior has been found in ferrite particles of similar size depending on the surrounding media. Also, the obtained results clearly provide evidence of the vastly different magnetic behavior for each ferrite system.Item Discussion on the Interparticle Interactions in NiFe2O4 and ZnFe2O4 Nanosized Systems Based on the Matrix Effects in the Magnetic Behavior(Journal of Physical Chemistry C, 2017) Virumbrales, Maider; Sáez Puche, Regino; Blanco Gutiérrez, Verónica; Torralvo Fernández, María JosefaZnFe2O4 and NiFe2O4 particles ranging from 5 to 8 nm have been prepared inside the channels of SBA-15 mesoporous material and nanowires were recovered after dissolving the silica matrix. For both ferrite compositions a hardening of the magnetic behavior has been obtained when using the mesoporous matrix. Thanks to the comparison of the magnetic behavior of the nanoparticles when contained and not in the matrix, it was possible to elucidate not only the matrix effect but also the kind of interparticle interactions depending on the ferrite composition. Thus, nickel ferrite particles are characterized by intense dipolar interactions that are responsible for the so high superparamagnetic response and that can be avoided by matrix effects only at high temperatures. On the contrary, the inherent low-intense dipolar interactions of the zinc ferrite system lead it to present lower superparamagnetic moments, and in the case of encapsulated particles, the superparamagnetic behavior would correspond to almost not-interacting particles. In addition, interactions occurring between surface spins of different particles are more visible in zinc ferrite system as consequence of its so low intense dipolar interactions and are prevented thanks to the use of the matrix.Item Thiol group functionalization of mesoporous SiO2 SBA-15 using supercritical CO2(Microporous and Mesoporous Materials, 2018) Tenorio, M.J.; Carnerero, C.; Torralvo Fernández, María Josefa; Pando García-Pumarino, Concepción; Cabañas Poveda, AlbertinaChemical modification of mesoporous SiO2 SBA-15 with thiol groups was performed using mercaptopropyltrimethoxysilane (MPTMS) dissolved in supercritical CO2 (scCO2). Thiol groups serve as adsorbents for the selective removal of contaminant metal cations and in catalysis. Functionalization was carried out in scCO2 at temperatures ranging from 40 to 150 °C and pressures from 15.0 to 29.0 MPa. For comparison purposes, the reaction was also performed in toluene at 80 and 110 °C. As opposed to toluene, scCO2 is considered a green solvent. Grafting of the thiol groups was confirmed by FTIR spectroscopy, thermogravimetric analysis (TGA) and elemental analysis. Grafting density and surface coverage of the materials modified using scCO2increased with temperature, CO2 density, time and stirring and varied from 1.3 to 4.4 mmol g−1 and from 1.3 to 4.0 molecules nm−2, respectively. On the other hand, surface area and pore size decreased as grafting density increased. At temperatures of 80 °C or higher, the pore size remained constant, suggesting the formation of a compact monolayer. Modification at higher temperatures led to larger grafting densities but very low surface areas. Assuming total hydrolysis and condensation of the precursor, the optimum grafting density and surface coverage of 2.3 mmol g−1 and 2.4 molecules nm−2, respectively, were obtained in scCO2 at 80 °C and 25.0 MPa for 4 h. Grafting densities of the samples prepared in toluene were by far much lower than those obtained using scCO2 at lower temperatures and shorter times, which demonstrates the advantages of CO2 as a green functionalization medium.Item Supercritical fluid deposition of Ru nanoparticles into SiO2 SBA-15 as a sustainable method to prepare selective hydrogenation catalysts(RSC Advances, 2015) Morère Rodríguez, Jacobo; Torralvo Fernández, María Josefa; Pando García-Pumarino, Concepción; Rodríguez Renuncio, Juan Antonio; Cabañas Poveda, AlbertinaRu nanoparticles were successfully deposited into mesoporous SiO2 SBA-15 using supercritical CO2 (scCO2). The use of scCO2 favoured the metal dispersion and Ru nanoparticles uniformly distributed throughout the support were obtained. Different precursors and methodologies were employed: impregnation with Ru(tmhd)2(COD) in scCO2 at 80 ºC and 13.5 and 19.3 MPa and further reduction in H2/N2 at 400 ºC at low pressure, reactive deposition of Ru(tmhd)2(COD) with H2 in scCO2 at 150 ºC and reactive deposition of RuCl3•xH2O with ethanol in scCO2 at 150 and 200 ºC. The size of the particles was limited in one dimension by the pore size of the support. The metal loading varied with the methodology and experimental conditions from 0.9 to 7.4% Ru mol. These materials exhibited remarkable catalytic activity. The Ru/SiO2 SBA-15 materials prepared by reactive deposition with H2 in scCO2 were selective catalysts for the hydrogenation reactions of benzene and limonene, allowing the production of partly hydrogenated hydrocarbons that may serve as building blocks for more complex chemicals. scCO2 is shown to be a green solvent that allows the preparation of efficient heterogeneous catalysts to design sustainable processes. Furthermore, in the hydrogenation of limonene, scCO2 was also used as the solvent.Item Particle size effect on the superconducting properties of YBa2Cu3O7-x particles(Dalton Transactions, 2017) Blanco-Gutiérrez, Verónica; Torralvo Fernández, María Josefa; Alario Franco, Miguel ÁngelYBCO samples with different microstructures were prepared after the thermal treatment of a precursor previously obtained by autocombustion. A drastic influence of the particle size on the magnetic behavior of the samples was observed. Thus, particles smaller than 110 nm do not exhibit superconducting pro-perties and for those ranging around 200 nm the diamagnetic signal characteristic of the superconduc-tivity at low temperature disappears in a large applied magnetic field. Particles larger than 300 nm do not exhibit the particle size effect. Accompanying such a phenomenon, an increase of the superconducting critical temperature is observed with the augmentation of the particle size, the lowest value being 18 K which corresponds to 110 nm particles.Item (Bi,R)2O3 (R: Nd, Sm and Dy) oxides as potential pigments(Journal of Alloys and Compounds, 2001) Gonzalvo, Borja; Romero de Paz, Julio; Fernández, Francisco; Torralvo Fernández, María JosefaIn this work we have tackled the feasibility of the colored oxides in the Bi2O3 –R2O3 system as ecological inorganic pigments.We have prepared by solid state reaction the mixed oxides (Bi2O3)1-x(R2O3)x , R: Nd, Sm and Dy, with nominal compositions: Nd, x=0.2 and 0.5; Sm, x=0.4; and Dy, x=0.35. The obtained orange (Bi2O3)0.6 (Sm2O3)0.4 and (Bi2O3)0.65(Dy2O3)0.35 oxides present f.c.c. fluorite-type structure. (Bi2O3)0.8(Nd2O3)0.2 oxide consists of a mixture of two phases which present f.c.c. d-Bi2O3 and Bi–Sr–O-type structures in the 900–1200 ºC temperature range. In the synthesis of the oxide with nominal composition (Bi2O3)0.5(Nd2O3)0.5 we have obtained a greenish sample with higher neodymium content. This sample presents the Bi3R5O12-type structure. Diffuse reflectance data and color coordinates suggest that the (Bi2O3)0.6(Sm2O3)0.4 and (Bi2O3)0.65(Dy2O3)0.35 oxides are expected to be promising candidates as new ecological pigments.