Browsing by Author "Ramirez, Galo"

Now showing 1 - 11 of 11
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    Effect of the Metal of a Metallic Ionic Liquid (-butyl-methylimidazolium tetrachloroferrate) on the Oxidation of Hydrazine
    (2024) Brockmann, Marcela; Navarro, Freddy; Ibarra, Jose; Leon, Constanza; Armijo, Francisco; Jesus Aguirre, Maria; Ramirez, Galo; Arce, Roxana
    This work investigates the electrocatalytic properties of carbon paste electrodes (CPEs) modified with ionic liquids (IL) and metallic ionic liquid (ILFe) for the hydrazine oxidation reaction (HzOR). The results indicate that ILFe significantly enhances the catalytic activity of the electrode, exhibiting catalysis towards hydrazine oxidation, reducing overpotential, and increasing reaction current. It is determined that the HzOR on the MWCNT/MO/ILFe electrode involves the transfer of four electrons, with high selectivity for nitrogen formation. Additionally, ILFe is observed to improve the wettability of the electrode surface, increasing its capacitance and reaction efficiency. This study highlights the advantages of ILFe-modified CPEs in terms of simplicity, cost-effectiveness, and improved performance for electrochemical applications, demonstrating how the ionic liquid catalyzes hydrazine oxidation despite its lower conductivity.
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    Electrical and Electrochemical Behavior of Carbon Paste Electrodes Modified with Ionic Liquids Based in N-Octylpyridinium Bis(Trifluoromethylsulfonyl)Imide. A Theoretical and Experimental Study
    (2019) Baez, Carla; Navarro, Freddy; Fuenzalida, Francesca; Aguirre, Maria J.; Carmen Arevalo, M.; Afonso, Maria; Garcia, Camilo; Ramirez, Galo; Antonio Palenzuela, J.
    In this work, we studied carbon paste electrodes (CPEs) with two kinds of binders: mineral oil or ionic liquids (IL) derived from N-substituted octyl pyridinium bis(trifluoromethylsulfonyl)imide with the substituents H-, CH3-, CN- and CF3-. The work aims to study this series of IL and determine a possible effect of the substituent of the cation in the behavior of the IL as a binder of graphite for obtaining IL-CPEs. The electrochemical response and the electrical behavior were measured by cyclic voltammetry and electrochemical impedance spectroscopy, respectively. Surprisingly, the substituent does not affect the cyclic voltammetry response because in all the cases, high resistance and high capacitive currents were obtained. The best response in terms of conductivity is obtained by CPE. In the case of impedance measurements, the substituent does not cause differences, and in all the cases, the IL-CPEs show nearly the same responses. CPE shows lower capacitance and higher resistance for diffusion compared to the IL-CPEs due to his lower porosity. The high resistance showed by the IL-CPEs by cyclic voltammetry can be attributed to poorly intermolecular forces among graphite, water, electrolyte, and ILs as demonstrated by theoretical calculations.
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    Electrochemical Detection of Sulfite by Electroreduction Using a Carbon Paste Electrode Binder with N-octylpyridinium Hexafluorophosphate Ionic Liquid
    (2022) Bustos Villalobos, Maicol; Ibarra, Jose; Gidi, Leyla; Cavieres, Valentina; Jesus Aguirre, Maria; Ramirez, Galo; Arce, Roxana
    Sulfite is a widely used additive in food and beverages, and its maximum content is limited by food regulations. For this reason, determining the sulfite concentration using fast, low-cost techniques is a current challenge. This work describes the behavior of a sensor based on an electrode formed by carbon nanotubes an ionic liquid as binder, which by electrochemical reduction, allows detecting sulfite with a detection limit of 1.6 +/- 0.05 mmol L-1 and presents adequate sensitivity. The advantage of detecting sulfite by reduction and not by oxidation is that the presence of antioxidants such as ascorbic acid does not affect the measurement. The electrode shown here is low-cost and easy to manufacture, robust, and stable.
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    Electrochemical oxidation of chlorpromazine, characterisation of products by mass spectroscopy and determination in pharmaceutical samples
    (2023) Martinez-Rojas, Francisco; Espinosa-Bustos, Christian; Ramirez, Galo; Armijo, Francisco
    The electrochemical behaviour of chlorpromazine (CPZ) at different pH values was studied using a fluorinedoped tin oxide (FTO) electrode. Cyclic voltammetry (CV), square-wave voltammetry (SWV), electrochemical impedance spectroscopy (EIS), and constant-potential electrolysis were used to elucidate the electrooxidation mechanism of CPZ on the FTO electrode, whereas chronoamperometry was used to determine CPZ in pharmaceutical and water samples. In addition, using mass spectrometry (MS), it was determined that the main oxidation product was the metabolite chlorpromazine sulfoxide (CPZ-SO). When electrolysis was performed at 1.45 V and pH 2, two metabolites were detected by MS, and a competitive mechanism was proposed wherein CPZ-SO was obtained simultaneously. Linear analytical curves were obtained between 2 x 10-6 and 100 x 10-6 mol L-1, and the detection limit was determined to be 0.26 x 10-6 mol L-1. The developed electroanalytical method thereby presents an appropriate sensitivity and stability that renders it suitable for use in the quality control and routine quantification of pharmaceutical formulations and samples containing environmentally relevant concentrations.
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    ELECTRODES MODIFIED BY Π STACKING OF METALLIC PHTHALOCYANINES AND ITS ELECTROCATALYTIC ACTIVITY ON NITRITE OXIDATION
    (2013) Navarrete, Natalia; Canales, Camila; Del Rio, Rodrigo; Ramirez, Galo
    In this work, it proposed the developing of a new material, a modified electrode with metallic phthalocyanines stacking columns, MxPc (Mx = Co, Fe and Ni), assembled by p interactions, which have a behavior as a supramolecular system. These electrodes showed an important electrocatalytic activity against nitrite oxidation, compared to the same complexes monomer multilayers adsorbed on the electrode (M-MxPc). It is proposed two new obtaining methods of these systems, S1-MxPc, where the complexes would form a column and would be coordinated with the surface electrode through a covalent bond of 4-aminopyridine (4-AP), and S2-MxPc, where the own functional groups of glassy carbon (GC) would be the covalent unions able to coordinate the complexes and the columns formation. These covalent unions between the electrode surface and phthalocyanines, would give a directional stacking, and therefore, would modify both its electrocatalytical activity and its electrical features.
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    Electrodetermination of Gallic Acid Using Multi-walled Carbon Nanotube Paste Electrodes and N-Octylpyridinium Hexafluorophosphate
    (WILEY-V C H VERLAG GMBH, 2022) Gidi, Leyla; Honores, Jessica; Ibarra, Jose; Jesus Aguirre, Maria; Arce, Roxana; Ramirez, Galo
    In this work, the determination of gallic acid was performed using surface-renewable carbon paste electrodes fabricated with multi-walled carbon nanotubes (MWCNT) and a mixture of N-octylpyridinium hexafluorophosphate (OPyPF6) ionic liquid with mineral oil (MO) as binder. This system shows remarkable amperometric sensor characteristics and promotes a better electronic transfer. An electroanalytical study of gallic acid shows a linear range from 4.98 +/- 0.25 to 74.1 +/- 2.2 mu mol L-1, with R-2=0.9958 and an experiment a limit of detection of 2.70 +/- 0.08 mu mol L-1 (S/N=3), and a sensitivity of 0.029 mu A mu mol(-1) L.
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    Hydrogen evolution reaction highly electrocatalyzed by MWCNT/N-octylpyridinum hexafluorophosphate metal-free system
    (2021) Gidi, Leyla; Arce, Roxana; Ibarra, Jose; Isaacs, M.; Aguirre, M. J.; Ramirez, Galo
    A mixed electrocatalyst that consists of multi walled carbon nanotubes (MWCNTs) and the ionic liquid (IL) N-octylpyridinum hexafluorophosphate (OPyPF6) as binder (MWCNT/IL system) was used in the study of hydrogen evolution reaction. This electrocatalyst was compared to graphite/mineral oil (Gr), graphite/OPyPF6 (Gr/IL), MWCNT/mineral oil (MWCNT) systems. All systems were characterized by cyclic voltammetry determining that MWCNT/IL system is highly electrocatalytic (E onset = -0.3 V vs Ag/AgCl) in relation to the other systems studied containing MWCNT or IL separately. The presence of each of the components that form the electrodic surface is corroborated by XRD, Raman, and FESEM-EDX, and it is demonstrated by chronoamperometric analysis that MWCNT/IL system is highly stable. The efficiency of the electrode, determined by its electrocatalytic activity, is confirmed by the quantification by gas chromatography of the hydrogen produced. Moreover, an elevated TON value (16274) and faradaic efficiency close to 60% are calculated, in comparison to other electrocatalysts found in literature. All these attractive properties are complemented by the fact that the MWCNT/IL system is simple, novel and easy to prepare. (C) 2021 Elsevier Ltd. All rights reserved.
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    Leyla Gidi, Camila Canales, Maria J. Aguirre, Francisco Armijo, and Galo Ramirez, Four-Electron Reduction of Oxygen Electrocatalyzed by a Mixture of Porphyrin Complexes onto Glassy Carbon Electrode (vol 13, pg 1666, 2018)
    (ESG, 2018) Gidi, Leyla; Canales, Camila; Aguirre, Maria J.; Armijo, Francisco; Ramirez, Galo
    © 2018 The Authors.The exact received date of the paper is 24 October 2017 year.
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    Nitrite electro-oxidation mediated by Co(II)-[tetra(4-aminophenyl)porphyrin]-modified electrodes: behavior as an amperometric sensor
    (TAYLOR & FRANCIS LTD, 2010) Rios, Roxana; Marin, America; Ramirez, Galo
    Electro-oxidation of nitrite mediated by Co(II)-[tetra(4-aminophenyl)porphyrin]-modified electrodes (4-CoTAPP) is presented in this article. Catalytic activity of electrodes modified with porphyrin polymeric films (poly-4-CoTAPP) and with multilayer of monomers (m-4-CoTAPP) for the oxidation of nitrite was compared. The number of cycles for the electrosynthesis of poly-4-CoTAPP determines the activity of the electrode toward nitrite oxidation because the system loses its catalytic activity as the number of polymerization cycles increases above 15. The effect of pH on activity is also reported. The response for the nitrite oxidation of electrodes modified with 4-CoTAPP and with metal-free ligand, that is, tetra(4-aminophenyl)porphyrin, either as multilayer of monomers or as polymer (m-4-H2TAPP and poly-4-H2TAPP, respectively), was compared. An increase of activity in the presence of the metal was found. Furthermore, when the device was tested as an amperometric sensor for different nitrite concentrations under the optimum working conditions, only poly-4-CoTAPP exhibited a linear response throughout the concentration range studied with a reasonably low limit of detection, while m-4-CoTAPP and poly-H2TAPP systems have no linear response throughout the range of concentration. Finally, the number of electrons involved and the Tafel slope for the reaction were estimated.
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    Study of the Hydrogen Evolution Reaction Using Ionic Liquid/Cobalt Porphyrin Systems as Electro and Photoelectrocatalysts
    (MDPI, 2020) Gidi, Leyla; Honores, Jessica; Ibarra, Jose; Arce, Roxana; Aguirre, M. J.; Ramirez, Galo
    In this work, the design and manufacture of graphite paste (Gr) electrodes is carried out, including N-octylpyridinium hexafluorophosphate (OPyPF6) ionic liquid (IL) as binder and modification with Co-octaethylporphyrin (Co), in order to study the hydrogen evolution reaction (HER) in the absence and presence of light. The system is characterized by XRD and FESEM-EDX (Field Emission Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy), confirming the presence of all the components of the system in the electrode surface. The studies carried out in this investigation confirm that a photoelectrocatalytic system towards HER is obtained. The system is stable, efficient and easy to prepare. Through cyclic voltammetry and electrochemical impedance spectroscopy, was determined that these electrodes improve their electrochemical and electrical properties upon the addition of OPyPF6. These effects improve even more when the systems are modified with Co porphyrin. It is also observed that when the systems are irradiated at 395 nm, the redox process is favored in energy terms, as well as in its electrical properties. Through gas chromatography, it was determined that the graphite paste electrode in the presence of ionic liquid and porphyrin (Gr/IL/Co) presents a high turnover number (TON) value (6342 and 6827 in presence of light) in comparison to similar systems reported.
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    α-Fe2O3/, Co3O4/, and CoFe2O4/MWCNTs/Ionic Liquid Nanocomposites as High-Performance Electrocatalysts for the Electrocatalytic Hydrogen Evolution Reaction in a Neutral Medium
    (2024) Ibarra, Jose; Aguirre, Maria Jesus; del Rio, Rodrigo; Henriquez, Rodrigo; Faccio, Ricardo; Dalchiele, Enrique A.; Arce, Roxana; Ramirez, Galo
    Transition metal oxides are a great alternative to less expensive hydrogen evolution reaction (HER) catalysts. However, the lack of conductivity of these materials requires a conductor material to support them and improve the activity toward HER. On the other hand, carbon paste electrodes result in a versatile and cheap electrode with good activity and conductivity in electrocatalytic hydrogen production, especially when the carbonaceous material is agglomerated with ionic liquids. In the present work, an electrode composed of multi-walled carbon nanotubes (MWCNTs) and cobalt ferrite oxide (CoFe2O4) was prepared. These compounds were included on an electrode agglomerated with the ionic liquid N-octylpyridinium hexafluorophosphate (IL) to obtain the modified CoFe2O4/MWCNTs/IL nanocomposite electrode. To evaluate the behavior of each metal of the bimetallic oxide, this compound was compared to the behavior of MWCNTs/IL where a single monometallic iron or cobalt oxides were included (i.e., alpha-Fe2O3/MWCNTs/IL and Co3O4/MWCNTs/IL). The synthesis of the oxides has been characterized by X-ray diffraction (XRD), RAMAN spectroscopy, and field emission scanning electronic microscopy (FE-SEM), corroborating the nanometric character and the structure of the compounds. The CoFe2O4/MWCNTs/IL nanocomposite system presents excellent electrocatalytic activity toward HER with an onset potential of -270 mV vs. RHE, evidencing an increase in activity compared to monometallic oxides and exhibiting onset potentials of -530 mV and -540 mV for alpha-Fe2O3/MWCNTs/IL and Co3O4/MWCNTs/IL, respectively. Finally, the system studied presents excellent stability during the 5 h of electrolysis, producing 132 mu mol cm(-2) h(-1) of hydrogen gas.