Person:
Fernández Sánchez, Paloma

First Name

Paloma

Last Name

Fernández Sánchez

URI

https://hdl.handle.net/20.500.14352/74998

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Ciencias Físicas

Department

Física de Materiales

Area

Ciencia de los Materiales e Ingeniería Metalúrgica

Identifiers

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Search Results

Now showing 1 - 10 of 26

In-depth structural and optical analysis of ce-modified zno nanopowders with enhanced photocatalytic activity prepared by microwave-assisted hydrothermal method
(Catalysts, 2020) Bazta, Otman; Urbieta Quiroga, Ana Irene; Trasobares, Susana; Piqueras de Noriega, Javier; Fernández Sánchez, Paloma; Addou, Mohammed; Calvino, Jose Juan; Hungría, Ana Belén
Pure and Ce-modified ZnO nanosheet-like polycrystalline samples were successfully synthesized by a simple and fast microwave-based process and tested as photocatalytic materials in environmental remediation processes. In an attempt to clarify the actual relationships between functionality and atomic scale structure, an in-depth characterization study of these materials using a battery of complementary techniques was performed. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM), energy-dispersive X-Ray spectroscopy-scanning transmission electron microscopy (STEM-XEDS), photoluminescence spectroscopy (PL) and UV-Visible absorption spectroscopy were used to evaluate the effect of Ce ions on the structural, morphological, optical and photocatalytic properties of the prepared ZnO nanostructures. The XRD results showed that the obtained photocatalysts were composed of hexagonal, wurtzite type crystallites in the 34-44 nm size range. The SEM and TEM showed nanosheet-shaped crystallites, a significant fraction of them in contact with bundles of randomly oriented and much smaller nanoparticles of a mixed cerium-zinc phase with a composition close to Ce_(0.68)Zn_(0.32)O_x. Importantly, in clear contrast to the prevailing proposals regarding this type of materials, the STEM-XEDS characterization of the photocatalyst samples revealed that Ce did not incorporate into the ZnO crystal lattice as a dopant but that a heterojunction formed between the ZnO nanosheets and the Ce-Zn mixed oxide phase nanoparticles instead. These two relevant compositional features could in fact be established thanks to the particular morphology obtained by the use of the microwave-assisted hydrothermal synthesis. The optical study revealed that in the ZnO:Ce samples optical band gap was found to decrease to 3.17 eV in the samples with the highest Ce content. It was also found that the ZnO:Ce (2 at.%) sample exhibited the highest photocatalytic activity for the degradation of methylene blue (MB), when compared to both the pure ZnO and commercial TiO_2-P25 under simulated sunlight irradiation. The kinetics of MB photodegradation in the presence of the different photocatalysts could be properly described using a Langmuir-Hinshelwood (LH) model, for which the ZnO:Ce (2 at.%) sample exhibited the highest value of effective kinetic constant.
LTA zeolite particles functionalized with nanomagnetite for effective recovery of dysprosium from liquid solutions
(Microporous and Mesoporous Materials, 2024) Alcaraz, Lorena; Sotillo Buzarra, Belén; Iglesias, Carlos; López, Félix A.; Fernández Sánchez, Paloma; Belviso, Claudia; Urbieta Quiroga, Ana Irene
Rare earth elements (REEs) as Dysprosium (Dy) are critical elements for the fabrication of components in many green energy technologies, from electric vehicles to wind turbines. Consequently, there is an increasing interest in creating sustainable and effective materials for the recovery and recycling of these elements. Zeolite materials have demonstrated a high affinity and selectivity for REEs. Thus, this paper aims to study the use of a synthetic LTA zeolite functionalized with nanomagnetite for Dy absorption, including a complete characterization of the synthetic zeolite, the kinetics and the factors affecting the adsorption efficiency. The maximum adsorption capacity reaches a value around 35 mg of Dy per gram of zeolite. The results from the adsorption isotherms and kinetic study revealed a good agreement with both Langmuir and Temkin models and pseudo-second-order kinetics. Furthermore, the thermodynamic analysis suggests that the adsorption of Dy onto the zeolite is a spontaneous and favorable process. The findings from this work could provide insights into the design and optimization of zeolite-based processes for REE recovery and recycling, contributing to the development of a more sustainable and circular economy.
ZnO nanoparticles with controllable Ce content for efficient photocatalytic degradation of MB synthesized by the Polyol method
(Catalysts, 2021) Flores Carrasco, Gregorio; Rodríguez Peña, Micaela; Urbieta Quiroga, Ana Irene; Fernández Sánchez, Paloma; Rabanal, María Eugenia
This paper reports on the synthesis of Ce-doped ZnO (CZO) nanoparticles (NPs) by an alternative polyol method at low temperature. The method, facile and rapid, uses acetate-based precursors, ethylene glycol as solvent, and polyvinylpyrrolidone as capping agent. The effects of the Ce-doping concentration (ranging from 0 to 8.24 atomic%) on the structural, morphological, compositional, optical, luminescence, and photocatalytic properties of the NPs were investigated by several techniques. The structural findings confirmed that the CZO NPs have a typical hexagonal wurtzite-type structure with a preferred orientation along the (101) plane. The results obtained by Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM) revealed that the NPs size decreased (from similar to 30 to similar to 16 nm) with an increase in the Ce-doping concentration. Energy Dispersive X-Ray Spectroscopy (EDS) and High Resolution Transmission Microscopy (HRTEM) results confirmed the incorporation of Ce ions into the ZnO lattice. Ce-doping influences the photoluminescence (PL) emission compared to that of pure ZnO. The PL emission is related to the presence of different kinds of defects, which could take part in charge transfer and/or trapping mechanisms, hence playing an essential role in the photocatalytic activity (PCA). In fact, in this work we report an enhancement of PCA as a consequence of Ce-doping. In this sense, the best results were obtained for samples doped with 3.24 atomic%, that exhibited a photocatalytic degradation efficiency close to 99% after 60 min ultraviolet (UV) illumination, thus confirming the viability of Ce-doping for environmental applications.
Recovery of niobium and tantalum by solvent extraction from Sn-Ta-Nb mining tailings
(RSC advances, 2020) Rodríguez, Olga; Alguacil, Francisco J.; Escudero Baquero, Esther; García Díaz, Irene; Fernández Sánchez, Paloma; Sotillo Buzarra, Belén; López, Félix A.
The slag from the extraction processes of metals from their ores may contain valuable components that, if adequately recovered, can be reintroduced in the technological life cycle. This is the case for the material obtained in Penouta mines in the North of Spain. These mineral sites are a main source of tin obtained from cassiterite. The mineral is submitted to a pyrometallurgical process to separate tin, however cassiterite is not the only mineral present in the veins, and large amounts of other minerals are normally discarded, constituting the slag. In the present case, besides cassiterite, one of the most abundant minerals in the ore is columbo tantalite, the source of the strategic coltan. In this work the raw material (slag) has been treated by acid leaching, using HF/H_2SO_4 as the leaching agent. Then liquid-liquid extraction of Nb and Ta was performed, with Cyanex ®923 extractant, so that both metals were obtained separately. Then they were precipitated from the corresponding aqeuous solution, and calcined in order to yield Nb_2O_5 of 98.5% purity and tantalum salt, after calcination and purification, of 97.3% purity. The process described in this work opens a possibility to produce high quality materials that are considered critical by the EU from alternative sources exempt of criticality factors.
Waveguide tapers fabrication by femtosecond laser induced element redistribution in glass
(Journal of lightwave technology, 2020) Macías Montero, Manuel; Dias, Antonio; Sotillo Buzarra, Belén; Moreno Zárate, Pedro; Ariza, Rocío; Fernández Sánchez, Paloma; Solís, Javier
Here in we present the fabrication and performance of waveguide tapers produced by femtosecond laser induced element redistribution in modified phosphate glasses. More particularly, it is demonstrated that by controlling the scan velocity during the writing process it is possible to adequately tune both the size of the modified area and the refractive index contrast to produce waveguides that can cope with mode field diameters in the range of 7 mu m. In addition, we fabricated tapered structures through the induction of an acceleration in the laser scanning velocity, resulting in a device that can efficiently convert a wide range of mode fields. The fine control achieved over the index contrast in the range of 10^(-3) and 10^(-2) would allow the production of a wide variety of tapers that could potentially be used to couple numerous photonic devices.
Photocatalytic activity of electric-arc furnace flue dusts
(Journal of materials research and technology, 2020) Alcaraz, Lorena; Urbieta Quiroga, Ana Irene; Fernández Sánchez, Paloma; López, Félix A.
Two electric-arc furnace flue dusts, a waste generated during the steel production process, were characterized and their photocatalytic activity was assessed. Chemical composition by X-ray fluorescence (XRF) analysis identified that both dusts were principally formed by iron, zinc and chromium oxides. Structural characterization carried out by X-ray diffraction patterns (XRD), and micro-Raman measurements demonstrated that ZnFe_2O_4 (zinc ferrite), FeCr_2O_4 (chromite) and ZnO (zincite) are present in both waste dusts as majority phases. Scanning electron microscopy (SEM) images showed that both dusts are formed by nanoparticles with a globular and octahedral morphology characteristic of the type of flue dusts formation and the obtained phases. Cathodoluminescence (CL) spectra show the characteristics bands of spinel structure (ZnFe_2O_4) and Fe^(3+) emission. X-ray photoelectron spectroscopy (XPS) measurements indicate that Fe ions could be present in 2+ and 3+ oxidation state in the spinel structure, while zinc and chromium ions are in 2+ and 3+, respectively. In addition, the photocatalytic experiments demonstrated that the analyzed samples could be useful as photocatalyzed showing a degradation percentage above 75 %.
Obtention and characterization of ferrous chloride FeCl_2•4H_2O from water pickling liquors
(Materials, 2021) Alcaraz, Lorena; Sotillo Buzarra, Belén; Marco, Jose F.; Alguacil, Francisco J.; Fernández Sánchez, Paloma; López, Félix A.
As a hazardous waste, water pickling liquors must be properly treated. An alternative consists of promoting the formation of ferrous salts from this residue due to their higher ferrous content. Since FeCl_2•4H_2O is widely used in several applications, obtaining pure crystals of this material appears to be an interesting prospect. However, this compound has scarcely been investigated. In the present work, FeCl_2•4H_2O crystals were obtained from water pickling liquors. Their structural and morphological characteristics were investigated by X-ray diffraction, scanning electron microscopy as well as Mossbauer spectroscopy. In addition, the photoluminescence study of the obtained samples was also assessed. It was observed that after some aging time, the obtained crystals changed in colour from green to more yellowish. As such, the aged sample was also evaluated, and their structural characteristics were compared with the original crystals. Despite this, the obtained crystals exhibit a FeCl_2•4H_2O structure, which is not modified with the aging of the sample.
Project number: 104
Diseño de herramientas de dinamización del aula adaptables a distintos escenarios de docencia (presenciales o en línea)
(2022) Fernández Sánchez, Paloma; Arroyo Bujase, Alex Miguel; Díaz-Guerra Viejo, Carlos; Fernández Jiménez, Rubén; Garrido Díaz, Esther; Hidalgo Alcalde, Pedro; Panis Maramba, Carlo Dexter; Romero Izquierdo, Carlos; Sotillo Buzarra, Belén; Urbieta Quiroga, Ana Irene
Role of the La/K Compositional Ratio in the Properties of Waveguides Written by Fs-Laser Induced Element Redistribution in Phosphate-Based Glasses
(Materials, 2020) Moreno-Zarate, Pedro; Muñoz, Francisco; Sotillo Buzarra, Belén; Macias-Montero, Manuel; Atienzar, Julia; Garcia-Pardo, Marina; Fernández Sánchez, Paloma; Serna, Rosalia; Solis, Javier
The local modification of the composition of glasses by high repetition femtosecond laser irradiation is an attractive method for producing photonic devices. Recently, the successful production of waveguides with a refractive index contrast (Δn) above 10−2 by fs-laser writing has been demonstrated in phosphate glasses containing La2O3 and K2O modifiers. This large index contrast has been related to a local enrichment in lanthanum in the light guiding region accompanied by a depletion in potassium. In this work, we have studied the influence of the initial glass composition on the performance of waveguides that are produced by fs-laser induced element redistribution (FLIER) in phosphate-based samples with different La and K concentrations. We have analyzed the contribution to the electronic polarizability of the different glass constituents based on refractive index measurements of the untreated samples, and used it to estimate the expected index contrast caused by the experimentally measured local compositional changes in laser written guiding structures. These estimated values have been compared to experimental ones that are derived from near field images of the guided modes with an excellent agreement. Therefore, we have developed a method to estimate before-hand the expected index contrast in fs-laser written waveguides via FLIER for a given glass composition. The obtained results stress the importance of considering the contribution to the polarizability of all the moving species when computing the expected refractive index changes that are caused by FLIER processes.
Preferential Growth of ZnO Micro- and Nanostructure Assemblies on Fs-Laser-Induced Periodic Structures
(Nanomaterials, 2020) Sotillo Buzarra, Belén; Ariza García, Rocío; Siegel, Jan; Solis, Javier; Fernández Sánchez, Paloma
In this work, we demonstrate the use of laser-induced periodic surface structures (LIPSS) as templates for the selective growth of ordered micro- and nanostructures of ZnO. Different types of LIPSS were first produced in Si-(100) substrates including ablative low-frequency spatial (LSF) LIPSS, amorphous-crystalline (a–c) LIPSS, and black silicon structures. These laser-structured substrates were subsequently used for depositing ZnO using the vapor–solid (VS) method in order to analyze the formation of organized ZnO structures. We used scanning electron microscopy and micro-Raman spectroscopy to assess the morphological and structural characteristics of the ZnO micro/nano-assemblies obtained and to identify the characteristics of the laser-structured substrates inducing the preferential deposition of ZnO. The formation of aligned assemblies of micro- and nanocrystals of ZnO was successfully achieved on LSF-LIPSS and a–c LIPSS. These results point toward a feasible route for generating well aligned assemblies of semiconductor micro- and nanostructures of good quality by the VS method on substrates, where the effect of lattice mismatch is reduced by laser-induced local disorder and likely by a small increase of surface roughness.