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
4 results
Search Results
Now showing 1 - 4 of 4
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.Item Deposition of Au nanoparticles into mesoporous SiO2 SBA-15(The Journal of Supercritical Fluids, 2022) Huerta, Andrea; Torralvo Fernández, María Josefa; Tenorio, María José; Pérez Velilla, Eduardo; Bermúdez, Jonathan; Calvo Garrido, María Lourdes; Cabañas Poveda, AlbertinaAu/SiO2 SBA-15 materials were prepared using supercritical CO2 (scCO2) and by wet impregnation. First, SiO2 SBA-15 was functionalized with thiol groups at different grafting densities using 3-(Mercaptopropyl)trimethoxysilane dissolved in scCO2. The support was then impregnated with HAuCl4·3H2O in scCO2 modified with EtOH. Wet impregnation of the supports with HAuCl4·3H2O in ethanol was also performed. Materials were calcined at 500 °C to remove the organic matter and promote particle growth. Materials prepared on the highest thiol grafting density support showed Au NP between 2.5 and 5 nm homogeneously distributed within the mesopores. Slightly larger Au NPs were obtained in scCO2 modified with EtOH. Materials prepared on the low thiol grafting density support showed a bimodal particle size distribution with particles up to 7 nm located inside the mesopores and larger ones of 10–20 nm on the external surface. A possible reaction mechanism was proposed. These materials can be used in catalysis, sensing and biomedicine.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 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.