Browsing by Author "Armijo, Francisco"

Now showing 1 - 12 of 12
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    Carbon dioxide electrochemical reduction by copper nanoparticles/ionic liquid-based catalytic inks
    (2024) Gazzano, Valeria; Mardones-Herrera, Elias; Saez-Pizarro, Natalia; Armijo, Francisco; Martinez-Rojas, Francisco; Ruiz-Leon, Domingo; Honores, Jessica; Isaacs, Mauricio
    The development of copper nanoparticle (CuNP)-based catalysts for the electrochemical reduction of carbon dioxide (ECO2-R) offers a promising approach to enhance its transformation into other industrially significant compounds. This study reports ECO2-R at -1.3 V vs RHE using CuNPs and catalytic inks composed of CuNPs and ionic liquids (ILs), observing significant differences in the selectivity of each catalyst. Specifically, CuNPs alone show a preference for producing ethylene and aqueous products, such as formic acid, ethanol, and formaldehyde. In contrast, the addition of ILs to the catalytic system redirects selectivity toward gaseous products, with methane being the main product. These findings highlight the potential to optimize catalyst composition to tailor the selectivity of CO2 conversion processes. ILs modify the catalytic environment and influence reaction pathways, enabling the selection of specific products.
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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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    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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    First approach of fractals nickel-copper dendrites on stainless steel electrodes for ammonia oxidation to nitrogen monitored in operando by differential electrochemical mass spectroscopy
    (2024) Matamala-Troncoso, Felipe; Diaz-Coello, Sergio; Martinez, Francisco; Barrientos, Herna; Lisoni, Judit; Armijo, Francisco; Lozano, David; Pizarro, Jaime; Arevalo, Maria del Carmen; Pastor, Elena; Aguirre, Maria Jesus
    Fractal nickel-copper dendrites were synthesized by electrochemical deposition (ECD) on a stainless steel electrode (SS/NiCu). The electrode surface was characterized using Field Emission Scanning Electron Microscopy (FE-SEM), X-ray diffractometry (XRD), and Raman spectroscopy. The Ni-Cu molar ratio and the time applied in the ECD method were studied, revealing that both are critical factors in modifying and controlling the surface morphology. The SS/NiCu electrodes show a higher density current response when exposed to ammonium hydroxide, reaching a limiting current density at concentrations above 0.050 M NH4OH. 4 OH. Ammonia oxidation reaction (AOR) was monitored in operando using differential electrochemical mass spectroscopy (DEMS). When a bias potential over +1.50 V (vs. RHE) was applied, the evolution of oxygen and NO was observed. However, N2 2 was the only oxidation product at a constant potential below +1.50 V (vs. RHE). Oxygen (O2) 2 ) evolution was the main competitive reaction during the AOR. The results show that products are strongly dependent on the electrochemical perturbation applied. The study demonstrated that the SS/NiCu electrodes are suitable for AOR to N2 2 in high alkaline conditions.
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    Formation of a Conducting Polymer by Different Electrochemical Techniques and Their Effect on Obtaining an Immunosensor for Immunoglobulin G
    (2023) Martinez-Sade, Erika; Martinez-Rojas, Francisco; Ramos, Danilo; Aguirre, Maria Jesus; Armijo, Francisco
    In this work, a conducting polymer (CP) was obtained through three electrochemical procedures to study its effect on the development of an electrochemical immunosensor for the detection of immunoglobulin G (IgG-Ag) by square wave voltammetry (SWV). The glassy carbon electrode modified with poly indol-6-carboxylic acid (6-PICA) applied the cyclic voltammetry technique presented a more homogeneous size distribution of nanowires with greater adherence allowing the direct immobilization of the antibodies (IgG-Ab) to detect the biomarker IgG-Ag. Additionally, 6-PICA presents the most stable and reproducible electrochemical response used as an analytical signal for developing a label-free electrochemical immunosensor. The different steps in obtaining the electrochemical immunosensor were characterized by FESEM, FTIR, cyclic voltammetry, electrochemical impedance spectroscopy, and SWV. Optimal conditions to improve performance, stability, and reproducibility in the immunosensing platform were achieved. The prepared immunosensor has a linear detection range of 2.0-16.0 ng center dot mL(-1) with a low detection limit of 0.8 ng center dot mL(-1). The immunosensing platform performance depends on the orientation of the IgG-Ab, favoring the formation of the immuno-complex with an affinity constant (Ka) of 4.32 x 10(9) M-1, which has great potential to be used as point of care testing (POCT) device for the rapid detection of biomarkers.
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    Growth direction and exposed facets of Cu/Cu2O nanostructures affect product selectivity in CO2 electroreduction
    (2022) Castro-Castillo, Carmen; Nanda, Kamala Kanta; Mardones-Herrera, Elias; Gazzano, Valeria; Ruiz-Leon, Domingo; Jesus Aguirre, Maria; Garcia, Gonzalo; Armijo, Francisco; Isaacs, Mauricio
    The electrochemical reduction of CO2 to fuels and value-added chemicals on metallic copper is an attractive strategy for valorizing CO2 emissions. However, favoring the CO2 reduction over hydrogen evolution and exclusive control of selectivity towards C1 or C2+ products by restructuring the copper surface is a major chal-lenge. Herein, we exploit the differential orientation of the exposed facets in copper nanostructures that can tune the product selectivity in CO2 electroreduction. The Cu nanostructure with predominant {111} orientation produce C1 products only upon CO2 electroreduction at an applied potential of-1.3 V vs. reversible hydrogen electrodes (RHE), with 66.57% Faradaic efficiency (FE) for methane. Whereas the vertically grown copper nanostructures that are oriented in {110} direction have higher dislocation density and show greater CO2 electroreduction activity (>95%) at the same applied potential, with FE towards ethylene 24.39% and that of oxygenates 41.31%. FIA-DEMS analysis provided experimental evidence of selectivity of methane over methanol at higher overpotentials indicating the mechanism of methane formation occurs via *COH intermediate. The ethylene formation at a potential-1.0 V vs. RHE or more negative to it suggests a common intermediate for methane and ethylene on the vertically grown copper nanostructures. This work advances the understanding between the product selectivity and the surface structure of the copper nanostructures in electrochemical CO2 reduction.
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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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    Marine biocorrosion inhibition of Pseudomonas sp. biofilms on 304 stainless steel coated with poly-6-aminoindole produced by two different electrochemical methods
    (2024) Castaneda, Erik; Castillo, Javiera; Pascual, Marta; Rubio, Francisca; Vargas, Ignacio; De la Iglesia, Rodrigo; Armijo, Francisco
    Forming a bacterial biofilm on a metallic surface could result in biocorrosion and biofouling development. New environmentally friendly coatings are required to protect infrastructure, especially in coastal and marine environments. This study aimed to evaluate the mitigation of biocorrosion produced by Pseudomonas sp. biofilms on AISI 304 stainless steel (SS304) coupons modified with poly-6-aminoindole (PAIn) using two electrochemical techniques: cyclic voltammetry (SS/6-PAIn CV) and chronoamperometry (SS/6-PAIn CA). Experimental trials were performed in two stages: (i) the settlement and colonization of bacteria (1 h of incubation) and (ii) biofilm development (7 days of incubation). Colonized surfaces were characterized by epifluorescence and field emission scanning electron microscopy. Biocorrosion mitigation was evaluated using linear resistance polarization, electrochemical impedance spectroscopy, and linear scanning voltammetry in simulated seawater at 20 degrees C. The results showed biofilm formation on SS304 and SS/6-PAIn CA, but in SS/6-PAIn CV, the coating considerably reduced biofilm formation, with alterations in the size and structural organization of the biofilm. The biofilm cover percentages were 31.63 %, 22.66 %, and 9.25 % for SS304, SS/6-PAIn CA, and SS/6-PAIn CV, respectively. Thus, SS/6-PAIn CV reduced biofilm growth by 70.76 % compared to bare SS after seven days of culture. Electrochemical parameters determined by LSV and EIS showed a significant improvement in charge transfer resistance and coating resistance for the SS/6-PAIn CV compared to the coating produced by chronoamperometry. Although both coatings protected the metallic surface, SS/6-PAIn CV presented the best protective properties, emerging as a promising alternative coating to mitigate the biocorrosion process of SS304 in a marine environment.
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    MODIFICATION OF BORON DOPED DIAMOND ELECTRODES WITH GLUCOSE OXIDASE, CHARACTERIZATION BY ELECTROCHEMICAL TECHNIQUES
    (SOC CHILENA QUIMICA, 2011) Del Rio, Rodrigo; Armijo, Francisco; Schrebler, Ricardo; Del Canto, Gabriela; Vergara, Claudia; Gutierrez, Cesar
    In this work, we report the effect of the direct successive modifications with Glucose oxidase onto boron doped diamond electrode (BDD). The modification due to the enzyme adsorption, on the potentiodynamic response of the electrode, was evaluated using Fe(CN)(6)(4-/3-) red-ox couple on the electrolyte and the Delta Ep variations were related with the number of modifications. Contact angle measurements and the electrochemical impedance spectra were also used to characterized the modifications and they showed variations in the same way that the potentiodynamic data.
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    Modification of composites of block copolymers-gold nanoparticles with enzymes and their characterization by electrochemical techniques
    (SPRINGER, 2011) Del Rio, Rodrigo; Armijo, Francisco; Schrebler, Ricardo; Gutierrez, Cesar; Amaro, Andrea; Biaggio, Sonia R.
    In this work, the poly(styrene-vynil pyridine) block copolymer was used as a porous pattern to study the electrodeposition of gold inside the pores, as a new method to obtain gold nanoparticles. The porous pattern left by the copolymer film onto a conductive glass surface was characterized by atomic force microscopy (AFM), evidencing pores of 30 nm diameter. After the electrodeposition, 30 nm diameter gold nanoparticles were obtained and they were characterized by cyclic voltammetry (CV) and AFM, and then used to study the adsorption of glucose oxidase enzyme. The adsorption process of glucose oxidase on gold nanowires was investigated by CV and electrochemical impedance spectroscopy. The morphological and capacitance results indicate that the block copolymer-gold nanoparticle composite seems to be a good candidate to design biosensors and immunosensors.
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    Reduced Graphene Oxide Overlayer on Copper Nanocube Electrodes Steers the Selectivity Towards Ethanol in Electrochemical Reduction of Carbon Dioxide
    (2022) Mardones-Herrera, Elias; Castro-Castillo, Carmen; Nanda, Kamala Kanta; Veloso, Nicolas; Leyton, Felipe; Martinez, Francisco; Saez-Pizarro, Natalia; Ruiz-Leon, Domingo; Jesus Aguirre, Maria; Armijo, Francisco; Isaacs, Mauricio
    Developing copper-based electrocatalysts that favor high-value multi-carbon oxygenates is desired, given their use as platform chemicals and as a direct fuel for transportation. Combining a CO-selective catalyst with copper shifts the selectivity of CO2 electroreduction toward C-2 products. Herein, we developed a reduced graphene oxide (rGO)-modified copper nanocube electrocatalyst that could shift the selectivity of CO2 electroreduction towards ethanol (Faradaic efficiency 76. 84 % at -0.9 V vs. reversible hydrogen electrode (RHE)). Spectroelectrochemical Raman analysis reveals a higher population of *C2HxOy intermediates at -0.9 V vs. RHE on the rGO-modified copper nanocube electrocatalyst surface, which coincides with the highest faradaic efficiency of ethanol upon CO2 electroreduction at the same potential. Our results demonstrate that the rGO modification can enhance ethanol selectivity through a probable tandem electrocatalysis mechanism and provide insights into controlling electrocatalytic activity and product selectivity in the CO2 electroreduction reaction.
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    Thermal treatment under oxidative conditions increases the antioxidant and antiglycation activity of Chilean Tortola beans ( Phaseolus vulgaris)
    (2025) Cruz, Nadia; Basoalto-Cubillos, Aracely; Marquez, Katherine; Nina, Nelida; Vallejos-Almirall, Alejandro; Armijo, Francisco; Schmeda-Hirschmann, Guillermo; Avila, Felipe
    The influence of oxygen on the thermal treatment (TT) of secondary metabolite-enriched extracts (SMEEs) from T & oacute;rtola beans and procyanidin C1 (PC1) on the inhibition of advanced glycation end products (AGEs) generation in proteins was investigated. SMEE was incubated at 4 degrees C (control) or thermally treated at 60 degrees C for 2 h, at either 0 % O-2 (I) or 20 % O-2 (II). Treatments I and II increased the content of procyanidin dimers B2. Treatment II was more effective than the control or treatment I in preventing homocysteine oxidation and AGEs generation. TT of PC1 at 0 % or 20 % O-2 generated procyanidin dimers and tetramers. PC1 TT at 20 % O-2 exhibited higher oxidation potentials and lower IC50 values of fluorescent AGEs than those of controls or TT at 0 % O-2. These findings indicate that SMEE from T & oacute;rtola beans after treatment II changes the degree of polymerization and oxidation procyanidins, thereby increasing their antiglycation activity.