Preparación y estudio de nanocomposites magnéticos con diferente potencial de empleo

A día de hoy, el estudio de nanocomposites magnéticos se presenta como una línea deinvestigación bastante atractiva, considerando las particulares propiedades de losmateriales obtenidos a escala nanométrica y sus diferentes aplicaciones.Generalmente, las nanopartículas magnéticas de fórmula general MFe2O4 con M = Fe2+,Co2+ y Ni2+ muestran comportamientos magnéticos diferentes en función del catióninvolucrado en la composición y del tamaño de partícula que conforma estas muestras.Un tamaño de partícula dentro del rango nanométrico genera el comportamientosuperparamagnético de algunas muestras, permitiendo la modulación de su respuestaante la presencia o ausencia de un campo magnético externo y, por consiguiente, suposible aplicación en biomedicina, (marcadores en resonancia magnética de imagen, entratamientos de liberación controlada de fármacos, hipertermia magnética, etc.) o enQuímica del medio ambiente.La tesis que se presenta se encuentra estructurada en tres partes y en ella se describe lasíntesis de núcleos de composición MFe2O4 con M = Fe2+, Co2+ o Ni2+ y surecubrimiento con cortezas diferentes (cortezas poliméricas biocompatibles y SiO2-APTES) para la obtención de nanocomposites magnéticos. Los primeros con ampliopotencial de aplicación en biomedicina y los segundos para su empleo como membranasadsorbentes de metales pesados..

Comparative study of core-shell nanostructures based on amino-functionalized Fe-4@SiO2 and CoFe2O4@SiO2 nanocomposites

Fe3O4@SiO2 and CoFe2O4@SiO2 and their corresponding amino-functionalized nanocomposites were successfully synthesized by a process of two steps including the preparation by coprecipitation or hydrothermal synthesis of the corresponding magnetic cores, the coating of its surface with a silica coating followed by its subsequent functionalization with 3-aminopropyltriethoxysilane (APTES). All magnetic samples were characterized by XRD using FULPROFF program, FTIR analysis, TEM and M-H hysteresis loops. The results showed diffraction maxima indexed in a cubic symmetry of S. G. Fd-3m with Z = 8 compatible with an inverse spinel-type structure. FTIR spectra of all samples show the characteristic bands of the magnetic cores and others bands corresponding to the asymmetric vibration of O-Si-O and Si-O-Si bonds of silica. The TEM images confirm that all the nanoparticles are coated, finding the largest thickness of the coating in the Fe3O4 sample prepared hydrothermally, which are the smaller ones. An expected reduction of the saturation magnetization of the magnetic cores is achieved with the coating and functionalization, although the behaviour of the Fe3O4 -samples remains practically superparamagnetic while the corresponding ones of cobalt are still ferrimagnetic. Fe3O4 nanocomposites respond to more quickly in the presence of an external magnetic field, something important against the removal of contaminating species in aqueous media. UV-Vis spectroscopy studies confirm the adsorption capacity of Cu2+ in aqueous solutions of the prepared nanocomposites, having found that a small thickness of the coating leads a greater adsorption, so that the best adsorption is found for CPFe3O4@SiO2-APTES nanocomposite. (C) 2018 Elsevier B.V. All rights reserved

Activated Carbons From Winemaking Biowastes for Electrochemical Double-Layer Capacitors

Revalorizing organic biowaste is critical to achieve a full circular economy, where waste is transformed into resources. One of the main strategies is to produce activated carbons and use them as functional materials for electrochemical energy storage. In this study, winemaking wastes, bagasse (BAG), and cluster stalks (CS) were recovered and used in the preparation of activated carbons by a hydrothermal process. Then, they were chemically activated using KOH and investigated for electrochemical capacitor applications. The activation treatment resulted in microporous structures, characterized by a type I isotherm for low partial pressures (P/P), and a type IV for higher pressures, as observed by Brunauer–Emmett–Teller surface analysis, with specific surfaces of 1,861 and 2,662 m·g for BAG and CS, respectively. These microporous structures were also investigated by means of scanning electron microscopy, revealing a high porous degree. Micro-Raman spectroscopy and X-ray photoelectron spectroscopy measurements displayed bands associated to disorder of the structure of the carbonaceous material. The electrochemical performance of the resulting materials was investigated for electrochemical energy storage applications, as supercapacitor electrode, in 1 M KOH aqueous electrolyte. These biowaste-derived materials displayed electrochemical double-layer capacitance, with 129 F·g at 10 A·g in the 0.1 to −1.0 V vs. saturated calomel electrode. For that reason, they are pin-pointed as potential negative electrodes for electrochemical double-layer supercapacitors and hybrid or asymmetric supercapacitors.Authors from Centro de Química Estrutural would like to thank the financial support of Fundação para a Ciência e a Tecnologia (FCT) under project numbers 1801P.00824.1.01, UID/QUI/00100/2019, and UIDB/00100/2020. We acknowledge support for the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI)

Coffee-derived activated carbon from second biowaste for supercapacitor applications

The electrochemical energy storage performance of activated carbons (ACs) obtained from coffee-derived biowastes was assessed. ACs were obtained from spent coffee ground second waste, after polyphenol extraction, by means of a hydrothermal process followed by physical or chemical activation. The resulting materials exhibited microporous structures with a total specific area between 585 and 2330 m·g. Scanning electron microscopy (SEM) revealed a highly porous microstructure in the case of the chemically activated carbons, while physical activation led to a cracked micro-sized morphology. The electrochemical properties of the materials for supercapacitor applications were investigated in 1 M NaSO. After chemical activation, the coffee-derived material displayed a capacitance of 84 F·g at 1 A·g in a 1.9 V voltage window, with 70% capacitance retention at 10 A·g and 85% retention after 5000 cycles of continuous charge-discharge. This work demonstrates how coffee secondary biowaste can be conveniently activated to perform as electrochemical energy storage material, contributing to its revalorization and reinsertion in a circular economy.Authors from Centro de Química Estrutural would like to thank the financial support of Fundação para a Ciência e a Tecnologia (FCT) under the project numbers numbers PTDC/QUI-ELT/28299/2017, UID/QUI/00100/2019 and UIDB/00100/2020

From bench-scale to prototype: case study on a nickel hydroxide—activated carbon hybrid energy storage device

Hybrid capacitors have been developed to bridge the gap between batteries and ultracapacitors. These devices combine a capacitive electrode and a battery-like material to achieve high energy-density high power-density devices with good cycling stability. In the quest of improved electrochemical responses, several hybrid devices have been proposed. However, they are usually limited to bench-scale prototypes that would likely face severe challenges during a scaling up process. The present case study reports the production of a hybrid prototype consisting of commercial activated carbon and nickel-cobalt hydroxide, obtained by chemical co-precipitation, separated by means of polyolefin-based paper. Developed to power a 12 W LED light, these materials were assembled and characterized in a coin-cell configuration and stacked to increase device voltage. All the processes have been adapted and constrained to scalable conditions to ensure reliable production of a pre-commercial device. Important challenges and limitations of this process, from geometrical constraints to increased resistance, are reported alongside their impact and optimization on the final performance, stability, and metrics of the assembled prototype.info:eu-repo/semantics/publishedVersio

Effects of shell-thickness on the powder morphology, magnetic behavior and stabilityof the chitosan-coated Fe3O4nanoparticles

Chitosan-coated Fe3O4nanoparticles were prepared by coprecipitation followed by reactionwith chitosan and different volumes of glutaraldehyde. Coating was modified by varyingthe volume of glutaraldehyde and reaction time. XRD pattern shows maxima compatibleFe3O4structure. FTIR spectroscopía confirms the presence of chitosan, more evident in sam-ples with higher chitosan content, as denoted by TGA. TEM images of samples with lowglutaraldehyde content reveal particles coated with a homogeneous chitosan shell. Mean-while, those prepared with high glutaraldehyde volume show nanoparticles dispersed in anorganic matrix. Samples present almost superparamagnetic behavior with magnetizationsaturation values that are reduced as the content of organic matter increases. Regarding thestability of these samples in solution, the presence of a homogeneous coating improves theinitial suspension, although it does not prevent its subsequent aggregation over time. How-ever, this aggregation process is reduced for sample synthesized with 1 mL of glutaraldehydeafter 6 h of reaction.Fundación Neurociencias y EnvejecimientoMINECODepto. de Química InorgánicaFac. de Ciencias QuímicasTRUEpu