Browsing by Autor "Luigi Manfredy"

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    Determinación electroquímica de ácido ascórbico sobre electrodos de carbón vítreo doblemente modificados
    (2014) Rossana Vásquez; Miguel Ángel Aguilar; Yris Martínez; M R Ricardo Hernández; Enrique J. Millán Barrios; Carlos Rojas; Luigi Manfredy; Reynaldo Luis Ortíz Ramos
    An electrochemical study of ascorbic acid (AA) determination on a modified glassy carbon (GC) electrode is reported. GC has been modified by using polyaniline (PANI) and H4PMo11VO40 (HPA). PANI was deposited on GV by repetitive cycling (60 scans) at -0.2 to 0.8V vs Ag/AgCl of a 50 mM aniline solution by employing 0.1M sulfuric acid as electrolyte solution. HPA was incorporated to the polymeric matrix by using a potential program. Scanning electron microscopy showed a porous and uniform morphology for PANI and PANI/PDA films, although PANI/PDA film showed a compacted structure.Differential pulse voltammetry (DPV) was used to quantify AA on a sulfate pH 2.04 buffer solution. We have found higher stability and better definition of the AA oxidation wave. Analytical analysis of the simple calibration curve for AA on the modified electrodes showed better response for the PANI electrode rather than de PANI/PDA electrode. Analysis of AA on the PANI modify electrode showed a linear response at 8 – 30 mM, 0.646 mM detection limit and 2.156 mM quantification limit. On the other hand, PANI/PDA showed a linear response range of 8-40 mM, detection limit of 1.240 mM and quantification limit of 4.134 mM.
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    DIMETILGLIOXIMA: un reactivo químico con 100 años de historia
    (2019) R. Contreras; Luis M. Barrientos-Contreras; Jerica M. Montilla-Suárez; Rubén A. Sánchez-Vargas; Luigi Manfredy
    La dimetilglioxima (diacetildioxima o butano-2,3-dioxima), dmgH2, es uno de los quelatos de uso más extendido en química de coordinación y analítica. La reacción de formación del bis(dimetilglioximato) de níquel(II), reportada por Lev A. Chugaev (Tschugaeff) en 1905, constituye una de las primeras pruebas específicas para la identificación cualitativa de un metal de transición. Desde entonces, y por más de un siglo, la dimetilglioxima adquirió importancia como un notable agente quelante, y sus compuestos complejos se han venido utilizando en áreas como la química inorgánica, catálisis, electroquímica, ciencia de materiales, entre otras. En este artículo, presentamos una breve revisión de la dimetilglioxima, los dimetilglioximatos metálicos y algunas de sus aplicaciones más representativas. La revisión indica que, además de su gran éxito como reactivo analítico para la determinación de metales, existen importantes estudios de los dimetilglioximatos metálicos como catalizadores de diversas reacciones, destacando la producción de hidrógeno molecular, una reacción de importancia por su impacto en la economía del hidrógeno y la química verde.
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    La celda y la batería redox de vanadio
    (2018) Keyla Márquez; Alexander Laguna; Milagro Yesenia Montilla Dávila; Domingo Alarcón; O.P. Márquez; P Jairo Márquez; Luigi Manfredy
    Redox flow batteries and in particular the vanadium redox flow battery (VRFB) are in an advanced state after many work performed in conversion, storage, supply of energy from natural sources or electrical energy and the many applications. These batteries when utilized for large scale grid storage must have long live, durability for large numbers of charge/discharge cycles, high round-trip efficiency, rapid response to changes and reasonable capital cost. The power and energy capacity of the vanadium redox flow battery (VRFB) system can be separated; the power of the system is determined by the number of cells in the stack and the size of the electrodes whereas the energy storage capacity is determined by the concentration and volume of the electrolyte. In this article we present a general view of the vanadium redox flow cell and battery, its composition, properties and applications, and some results obtained in our laboratory as the voltage (1.47), charge yield (92.37), voltage yield (87.13), energy yield (80.48), stability in charge/discharge cycles, rapid charging and low auto discharge are presented. A section of vanadium in our crudes is also incorporated.