Examinando por Materia "Absorption spectroscopy"
Mostrando 1 - 3 de 3
Resultados por página
Opciones de ordenación
Ítem Effect of CeO2 content in morphology and optoelectronic properties of TiO2-CeO2 nanoparticles in visible light organic degradation(ELSEVIER SCI LTD, 2019-02-01) Cano-Franco, JC; Alvarez-Lainez, M; Universidad EAFIT. Departamento de Ingeniería de Diseño; Ingeniería de Diseño (GRID)TiO2 is a semiconductor widely used in photocatalytic degradation of organic pollutants due to its band gap energy. However, its absorption range is restricted only to UV radiation that is less than 10% of solar light. With the aim of increasing the adsorption area on TiO2 nanoparticles a modified sol-gel method was used to produce a smaller particle size, and to extend the absorption range to the visible spectrum, TiO2 nanoparticles were synthesized with different CeO2 contents to generate semiconductor heterojunction between them. The crystallographic, morphological, and optoelectronic characteristics of these TiO2-CeO2 nanoparticles were studied, and two crystalline phases were differentiated: anatase for TiO2 and fluorite for CeO2. An increase in the CeO2 content produced crystallite sizes between 6.5 nm and 12.0 nm. TiO2-CeO2 nanoparticles showed morphological properties such as small particle size, heterogeneous surface and high BET surface area compared to bare commercial TiO2. These features involve a positive effect of CeO2 in TiO2 nanoparticles surface, thus TiO2-CeO2 nanoparticles exhibit enhanced optoelectronic properties caused by a decrease in the effective band gap and red-shift in the electromagnetic spectrum. In addition, methylene blue degradation showed that TiO2-CeO2 nanoparticles are suitable for high photocatalytic activity application under visible light. © 2018 Elsevier LtdÍtem Green synthesis of magnetic nanoparticles using leaf extracts of Aloe vera and Kalanchoe daigremontiana to remove divalent mercury from natural waters(IOP PUBLISHING LTD, 2019-01-01) Morales G.; Campillo G.; Vélez E.; Osorio J.; Urquijo J.; Velásquez Á.A.; Morales G.; Campillo G.; Vélez E.; Osorio J.; Urquijo J.; Velásquez Á.A.; Universidad EAFIT. Departamento de Ciencias; Electromagnetismo Aplicado (Gema)In this study, magnetic nanoparticles of magnetite were prepared by an eco-friendly method using aqueous leaf extracts of Aloe vera and Kalanchoe daigremontiana. These vegetal extracts have suitable characteristics such as high availability, low cost, and serve as good colloidal stabilizers. Synthetized products were characterized by Transmission Electron Microscopy (TEM), Room Temperature Mossbauer Spectroscopy (RT-MS), and their potential use as adsorbents for Hg (II) removal in natural waters was evaluated by Atomic Absorption Spectroscopy (AAS). Size distribution and morphology of the products obtained by TEM show spherical nanoparticles composites, with sizes between 3 and 10 nm for both extracts. Mossbauer spectra are consistent with superparamagnetic particles for both samples. Moreover, particles from both extracts showed mercury removal efficiencies above 75%. © Published under licence by IOP Publishing Ltd.Ítem Synthesis and characterization of magnetite-maghemite nanoparticles obtained by the high-energy ball milling method(Springer Netherlands, 2018-03-13) Velásquez, A. A.; Marín, C; Urquijo, P; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)We present the process of synthesis and characterization of magnetite-maghemite nanoparticles by the ball milling method. The particles were synthesized in a planetary ball mill equipped with vials and balls of tempered steel, employing dry and wet conditions. For dry milling, we employed microstructured analytical-grade hematite (a-Fe2O3), while for wet milling, we mixed hematite and deionized water. Milling products were characterized by X-ray diffraction, transmission electron microscopy, room temperature Mössbauer spectroscopy, vibrating sample magnetometry, and atomic absorption spectroscopy. The Mössbauer spectrum of the dry milling product was well fitted with two sextets of hematite, while the spectrum of the wet milling product was well fitted with three sextets of spinel phase. X-ray measurements confirmed the phases identified by Mössbauer spectroscopy in both milling conditions and a reduction in the crystallinity of the dry milling product. TEM measurements showed that the products of dry milling for 100 h and wet milling for 24 h consist of aggregates of nanoparticles distributed in size, with mean particle size of 10 and 15 nm, respectively. Magnetization measurements of the wet milling product showed little coercivity and a saturation magnetization around 69 emu g-1, characteristic of a nano-spinel system. Atomic absorption measurements showed that the chromium contamination in the wet milling product is approximately two orders of magnitude greater than that found in the dry milling product for 24 h, indicating that the material of the milling bodies, liberated more widely in wet conditions, plays an important role in the conversion hematite-spinel phase. © 2018, Springer Science+Business Media B.V., part of Springer Nature.