Browsing by Author "Isaacs, Mauricio "

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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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    CdTe quantum dots modified electrodes ITO-(Polycation/QDs) for carbon dioxide reduction to methanol
    (ELSEVIER, 2020) Guzman, Diego; Isaacs, Mauricio; Tsukuda, Tatsuya; Yamazoe, Seiji; Takahata, Ryo; Schrebler, Ricardo; Burgos, Ana; Osorio Roman, Igor; Castillo, Francisco
    The present work describes the characterization by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and electrochemical techniques of ITO modified electrodes with electrostatic assemblies (Polycation/Quantum Dots) and their use in the electro- and photoelectrocatalytic reduction of CO2. These assemblies were prepared with polycations poly-diallyldimethylammonium (PD) and poly-(2-trimethylammonium) ethyl methacrylate (PM) and nanocrystals of CdTe of 2.77 nm (Q2). The size of the nanocrystals was controlled by the synthesis reflux time and incorporated by electric field directed Layer-by-Layer assembly method (EFDLA). The polycations were characterised by NMR measurements; showing important effects on the electrostatic assemblies. PM modified electrodes, with its lower rigidity, exhibited less roughness than the PD modified electrodes, 8.0 nm versus 32.8 nm, and higher heterogeneity in its surface composition. Higher resistance to the charge transfer and time constants were obtained with PMQ2 modified electrode, 63.8 Omega cm(-2) and 2.69 ms versus 49.30 Omega cm(-2) and 1.3 ms for PDQ2. The electro- and photoelectro properties for CO 2 reduction were studied through j-E curves and potential controlled electrolysis. Modified surfaces were active toward the reduction of CO2, with a positive shift of the activity between darkness and irradiation conditions, 0.050 V with PDQ2 and 0.450 V with PMQ2. The main product of the CO2 reduction was CH3OH, with traces of CO and HCOOH. The PM modified electrodes with QDs of 2.77 nm presented a selective behaviour for the production of CH3OH.
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    Cysteine-Mediated Green Synthesis of Copper Sulphide Nanoparticles: Biocompatibility Studies and Characterization as Counter Electrodes
    (2022) Saona, Luis A.; Campo-Giraldo, Jessica L.; Anziani-Ostuni, Giovanna; Ordenes-Aenishanslins, Nicolas; Venegas, Felipe A.; Giordana, Maria F.; Diaz, Carlos; Isaacs, Mauricio; Bravo, Denisse; Perez-Donoso, Jose M.
    A one-pot green method for aqueous synthesis of fluorescent copper sulphide nanoparticles (NPs) was developed. The reaction was carried out in borax-citrate buffer at physiological pH, 37 degrees C, aerobic conditions and using Cu (II) and the biological thiol cysteine. NPs exhibit green fluorescence with a peak at 520 nm when excited at 410 nm and an absorbance peak at 410 nm. A size between 8-12 nm was determined by dynamic light scattering and transmission electron microscopy. An interplanar atomic distance of (3.5 +/- 0.1) A and a hexagonal chalcocite crystalline structure (beta Ch) of Cu2S NPs were also determined (HR-TEM). Furthermore, FTIR analyses revealed a Cu-S bond and the presence of organic molecules on NPs. Regarding toxicity, fluorescent Cu2S NPs display high biocompatibility when tested in cell lines and bacterial strains. Electrocatalytic activity of Cu2S NPs as counter electrodes was evaluated, and the best value of charge transfer resistance (R-ct) was obtained with FTO/Cu2S (four layers). Consequently, the performance of biomimetic Cu2S NPs as counter electrodes in photovoltaic devices constructed using different sensitizers (ruthenium dye or CdTe NPs) and electrolytes (S2-/S-n(2-) or I-/I3-) was successfully checked. Altogether, novel characteristics of copper sulfide NPs such as green, simple, and inexpensive production, spectroscopic properties, high biocompatibility, and particularly their electrochemical performance, validate its use in different biotechnological applications.
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    Experimental and theoretical study of synthesis and properties of Cu2O/ TiO2 heterojunction for photoelectrochemical purposes
    (2023) Matamala-Troncoso, Felipe; Saez-Navarrete, Cesar; Mejia-Lopez, Jose; Garcia, Griselda; Rebolledo-Oyarce, Jose; Nguyen, Cuong Ky; MacFarlane, Douglas R.; Isaacs, Mauricio
    The Cu2O/TiO2 heterojunction is an attractive surface for its optoelectronic properties for developing catalysts, cells, and solar devices. However, the mechanisms involved in synthesizing an electrode using the Cu2O/TiO2 heterojunction can affect the surface properties and the surface/electrolyte interactions. In this work, we studied the formation mechanism of the Cu2O/TiO2 heterojunction by electrochemical deposition (ECD) of Cu2O mol-ecules on TiO2 nanoparticles previously deposited on a fluorine-doped thin oxide coated glass substrate (FTO). The photoelectrochemical properties of the Cu2O/TiO2/FTO electrode were characterized by XRD, FE-SEM, TEM, EDX, UV-vis diffuse reflectance spectroscopy (DRS), Raman spectroscopy, and electrochemical methods. Theoretical methods such as ab-initio density functional theory calculations and molecular dynamics simulations were used to understand the experimental results. The analysis carried out by theoretical methods allowed us to identify the initial steps of the formation mechanism of Cu2O molecules on TiO2 nanoparticles. Theoretical calculations demonstrated that forming a Cu2O nanowire-like network on the TiO2 nanoparticle matrix favors the charge transfer at the electrolyte/semiconductor interface, promoting the behavior of the electrode as a cathode. Finally, the Cu2O/TiO2/FTO electrode synthesized was used to perform the reduction photoelectrocatalyzed of nitrate to ammonia under illumination with a Xe-Hg arc lamp and applying-0.5 V bias potential (vs Ag/AgCl sat.) to evaluate the performance of the electrode as a cathode.
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    Facile methodology to generate Cu2O/TiO2 heterojunction on FTO electrode for photoelectroreduction of nitrate
    (2021) Matamala-Troncoso, Felipe; Nguyen, Cuong Ky; MacFarlane, Douglas R.; Isaacs, Mauricio; Saez-Navarrete, Cesar
    Easy and low-cost synthesis of a Cu2O/TiO2/FTO electrode is proposed. The Cu2O/TiO2 heterojunction was synthesized by sintering TiO2 nanoparticles on an FTO electrode surface, followed by a Cu2O electrochemical deposition step. Characterization of the electrode was performed by FE-SEM-EDX microscopy, Raman and UV-Vis DR spectroscopy, and electrochemical methods. The photoelectrochemical behavior was characterized, and the p-type character material was confirmed. The reduction of nitrate to nitrite was performed using the Cu2O/TiO2/FTO electrode under Xe lamp illumination with lower overpotentials than those commonly used in this electrochemical process. Nitrate/nitrite conversion was achieved with a promising result of about 22% conversion at-0.05 V RHE. (C) 2021 Elsevier B.V. All rights reserved.
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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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    Highly efficient hydrogen evolution reaction, plasmon-enhanced by AuNP-l-TiO2NP photocatalysts
    (2020) Castillo-Rodriguez, Judith ; Ortiz, Pedro D. ; Isaacs, Mauricio ; Martinez, Natalia P. ; O’Shea, James N. ; Hart, Jack ; Temperton, Robert ; Zarate, Ximena ; Contreras, David ; Schott, Eduardo
    A set of AuNPs-l-TiO2NP nanoaggregates which showed efficient covering of the semiconductor's surface by AuNPs, as well as appropriate AuNP sizes for effective sensibilization were used as photocatalysts for the hydrogen evolution reaction (HER). Three aliphatic short-chain linkers: 3-mercaptopropionic acid (MPA), thioglycolic acid (TGA) and thiolactic acid (TLA) were used as stabilizing agents. The slight structure variations of the linkers did not produce differences in the AuNP size and morphology. However, it was interesting to show how the photocatalytic performance of the nanoaggregates is dependent on the linker present, as well as to determine the influence of the Au/TiO(2)ratio. It was found that TGA gave the best performance at a longer irradiation time, though high amounts of H(2)were also obtained for the other two linkers. Furthermore, for all samples large amounts of hydrogen were obtained, which are significantly higher than that usually obtained with plasmon-sensitized TiO(2)nanostructures. In addition, high amounts of H(2)were obtained after five catalytic cycles for all samples, showing the suitability of these nanoaggregates for the photoinduced HER.
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    Hydrogen Productivity Analysis Using Low Concentration of TiO2-Au Nanoparticles on a Ultraviolet-LED-Based Photocatalytic Reactors
    (2021) Varas Concha, Felipe; Guzman, Diego; Isaacs, Mauricio; Saez Navarrete, Cesar
    The productivity of photocatalytic hydrogen generation via photo-reforming of organic compounds has not been studied under low concentrations of catalyst, which could lead to relevant cost savings in future real-scale applications. Herein, it uses half of the lowest concentration of nanoparticles reported of modified P25 TiO2 partially coated with gold. The nanomaterial is prepared using a non-energy intensive, chemical reduction method. Gold content on the TiO2 surface is reported (14%-surface; 9.1%-weight). Dynamic light scattering and transmission electron microscope image analyses show low agglomeration and non-homogeneous shape. Aggregates and gold nanoparticles reach average diameters of 92 and 3.8 nm, respectively. Photocatalytic experiments for hydrogen production are carried out at low concentration of nanoparticles (0.056 g L-1) in methanol-water solution (5%vol.) under 375 nm UV and visible light (20 mW cm(-2)). The system shows a catalyst productivity of 6661 mu mol h(-1) g(-1), a third of the highest reported productivity using methanol (which used a catalyst concentration 18x higher, an alcohol concentration 5x higher, and 100% anatase). The system shows an estimated reaction rate of 373 mu mol L-1 h(-1) with an apparent zero order kinetic, an overall energy conversion efficiency of 0.47%, and an apparent quantum yield of 1.03%.
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    Improving myoblast differentiation on electrospun poly(ε-caprolactone) scaffolds
    (2017) Abarzua-Illanes, Phammela N.; Padilla, Cristina; Ramos, Andrea; Isaacs, Mauricio; Ramos Grez, Jorge; Olguin, Hugo C.; Valenzuela, Loreto M.
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    Multimetallic porphyrins/polyoxotungstate modified electrodes by layer-by-layer method: Electrochemical, spectroscopic and morphological characterization
    (PERGAMON-ELSEVIER SCIENCE LTD, 2012) Garcia, Macarena; Carfuman, Karla; Diaz, Carlos; Garrido, Carlos; Osorio Roman, Igor; Jesus Aguirre, M.; Isaacs, Mauricio
    This work describes the formation of modified electrodes layer-by-layer assembly of a mu-{meso-5,10,15,20-tetra(pyridyl)porphyrin}terrakis{bis(bipyridine)chloride ruthenium(II)} coordinated with Zn(II) and Mn(III) in its central cavity and an anionic polyoxotungstate [SiW12O40](4-). The bilayer formation was monitored using electrochemical and UV-vis techniques, following the oxidation process of the Ru-III/II couple and the absorbance of the Soret band of porphyrin complexes respectively. It was possible to form 10 stable bilayers onto ITO surface. SEM studies were carried out finding that the morphology of the film depends on the metal center in the porphyrin. The thickness of these films was estimated as 0.603 mu m for (Zn(II)TRP](4+)/[SiW12O40](4-) and 2.18 mu m for [Mn(III)TRP](5+)/[[SiW12O40](4-) modified electrodes respectively. Raman spectroscopy showed that new bands appeared for [Mn(III)TRP](5+)/[SIW12O40](4-) assembly confirming stronger interactions than only electrostatic forces.
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    New Hybrid Copper Nanoparticles/Conjugated Polyelectrolyte Composite with Antibacterial Activity
    (2021) Jessop, Ignacio A.; Perez, Yasmin P.; Jachura, Andrea; Nunez, Hipolito; Saldias, Cesar; Isaacs, Mauricio; Tundidor-Camba, Alain; Terraza, Claudio A.; Araya-Duran, Ingrid; Camarada, Maria B.; Carcamo-Vega, Jose J.
    In the search for new materials to fight against antibiotic-resistant bacteria, a hybrid composite from metallic copper nanoparticles (CuNPs) and a novel cationic pi-conjugated polyelectrolyte (CPE) were designed, synthesized, and characterized. The CuNPs were prepared by chemical reduction in the presence of CPE, which acts as a stabilizing agent. Spectroscopic analysis and electron microscopy showed the distinctive band of the metallic CuNP surface plasmon and their random distribution on the CPE laminar surface, respectively. Theoretical calculations on CuNP/CPE deposits suggest that the interaction between both materials occurs through polyelectrolyte side chains, with a small contribution of its backbone electron density. The CuNP/CPE composite showed antibacterial activity against Gram-positive (Staphylococcus aureus and Enterococcus faecalis) and Gram-negative (Escherichia coli and Salmonella enteritidis) bacteria, mainly attributed to the CuNPs' effect and, to a lesser extent, to the cationic CPE.
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    Phenoxy- and Phenylamino-Heterocyclic Quinones: Synthesis and Preliminary Anti-Pancreatic Cancer Activity
    (WILEY-V C H VERLAG GMBH, 2022) Sanchez, Patricio; Salas, Cristian O.; Gallardo-Fuentes, Sebastian; Villegas, Alondra; Veloso, Nicolas; Honores, Jessica; Inman, Martyn; Isaacs, Mauricio; Contreras, Renato; Moody, Christopher J.; Cisterna, Jonathan; Brito, Ivan; Tapia, Ricardo A.
    The successful application of fragment-based drug discovery strategy for the efficient synthesis of phenoxy- or phenylamino-2-phenyl-benzofuran, -benzoxazole and -benzothiazole quinones is described. Interestingly, in the final step of the synthesis of the target compounds, unusual results were observed on the regiochemistry of the reaction of bromoquinones with phenol and aniline. A theoretical study was carried out for better understanding the factors that control the regiochemistry of these reactions. The substituted heterocyclic quinones were evaluated in vitro to determine their cytotoxicity by the MTT method in three pancreatic cancer cell lines (MIA-PaCa-2, BxPC-3, and AsPC-1). Phenoxy benzothiazole quinone 26a showed potent cytotoxic activity against BxPC-3 cell lines, while phenylamino benzoxazole quinone 20 was the most potent on MIA-PaCa-2 cells. Finally, electrochemical properties of these quinones were determined to correlate with a potential mechanism of action. All these results, indicate that the phenoxy quinone fragment led to compounds with increased activity against pancreatic cancer cells.
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    Photocatalyzed Production of Urea as a Hydrogen–Storage Material by TiO2–Based Materials
    (2022) Matamala-Troncoso, Felipe; Isaacs, Mauricio ; Sáez-Navarrete, César
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    Quick and Easy Modification of Glassy Carbon Electrodes with Ionic Liquid and Tetraruthenated Porphyrins for the Electrochemical Determination of Atrazine in Water
    (2019) Calfuman, Karla; Honores, Jessica; Isaacs, Mauricio; Quezada, Diego; Valdebenito, Javier; Urzua, Marcela
    Atrazine is a pesticide used to control broadleaf weeds, however its wide distribution and its high persistence in the soil and in surface waters has resulted in a public and environmental health problem. Present results shows the design, construction and characterization of glassy carbon electrodes modified with tetrarutenated metalloporphyrin (M=Ni (II) and Zn (II)) and 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide, BMIMNTF2. The modification was reproducible and sensitive for the electrochemical detection of atrazine in neutral media. The detection limit was 230 nM when using GC/BMIMNTF2/ZnTRP and 540 nM with GC/BMIMNTF2/NiTRP, meaning that his methodology can be a feasible and inexpensive way to detect atrazine in trace levels.
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    Recent studies on polymer electrolytes containing ionic liquids and their applications in lithium-ion batteries
    (2023) Marquina, Luigi Manfredy; Riveros, Lyda La Torre; Ccana, Victor Jauja; Muedas-Taipe, Golfer; Isaacs, Mauricio; La Rosa-Toro, Adolfo
    One of the most important challenges in battery research is to achieve safer devices with enhanced electrochemical performance. Including ionic liquids (ILs) in developing polymeric electrolyte systems for batteries is an interesting approach to improve some properties such as flexibility, thermal stability, safety and minimizing electrolyte dripping in the devices. An additional advantage of polymeric electrolytes is the possibility of replacing the separator, which reduces one of the battery components, thereby reducing costs and facilitating its manufacture. In recent years, interest has increased in polymeric electrolytes for lithium-ion batteries (LIBs) applied to solid polymer electrolytes (SPEs), gel polymer electrolytes (GPEs) and composite-polymer electrolytes (CPEs) that use ILs, resulting nowadays as one of the most fascinating topics in energy storage devices.
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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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    Suitability study of Ag nanosheet SERS substrates as a screening method for imidacloprid after QuEChERS extraction
    (2024) Leyton-Soto, Felipe; Schultz, Zachary D.; Ormazabal-Toledo, Rodrigo; Ruiz-Leon, Domingo; Giordano, Ady; Isaacs, Mauricio
    With the current food demand, pesticides have become some of the most important compounds to maintain food quality; however, this requires the development of methodologies that allow fast, sensitive, and low-cost screening for these contaminants. Surface-enhanced Raman spectroscopy is an emerging solution since the interaction between the analyte and metallic nanostructures increases the Raman signals, enabling trace detection and a chemical-specific measurement. In this way, the fast detection of contaminants is possible, and further advances may enable portable assays. In this work, SERS substrates with silver nanosheets (AgNSs) on a copper surface were synthesized, producing a strong SERS effect and a reproducible signal intensity from methylene blue probe molecules at an optimal reaction time of 1 min. A quantitative analysis of the pesticide imidacloprid was then performed by applying a PLSR chemometric model, revealing a high linear correlation between the reference values and the predicted values of the pesticide (Rcv2 = 0.9732 and RMSECV = 0.1239). AgNS substrates were used to determine the feasibility of using this methodology for screening imidacloprid in real bee honey samples obtained through QuEChERS extraction, and an average recovery of 75.5% +/- 0.08 was obtained. In addition, density functional theory simulations were carried out to elucidate the possible molecular interaction with the SERS surface and to assign the observed vibrational modes of imidacloprid. SERS is thus demonstrated to be an alternative to conventional pesticide detection techniques.
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    Synthesis and characterization of low-melting ferrocenyl salts: a study of thermal and photochemical redox reactions
    (2018) Diaz, Carlos; Ferraudi, Guillermo; Lappin, A. Graham; Oliver, Allen; Isaacs, Mauricio
    The syntheses of bis(trifluoromethane) sulfonimide N-(ferrocenylmethyl) N,N,N-trimethyl ammonium salt 1 and bis(trifluoromethane) sulfonimide N',N-bis(ferrocenylmethyl) inmidazolium salt 2 are reported. The compounds show low melting points, 76 degrees and 125 degrees C, respectively, and were characterized by spectroscopic techniques H-1-NMR, mass spectrometry, FT-IR spectroscopy, cyclic voltammetry, and XRD crystallographic analysis. Cyclic voltammetry results demonstrate that both salts have a quasi-reversible electrochemical behavior, similar to the reversible one shown by ferrocene under the same conditions. In the case of 1, a coupled chemical reaction was detected at slow scan rates after the oxidation. Transient species in the redox processes were investigated using flash photolysis and pulse radiolysis. In both cases, transient spectra of the products were similar to transient spectra observed for ferrocene. The decay kinetics of the oxidized and reduced transients were examined and mechanistic information was obtained. The experimental results show the potential uses of the two complexes as catalytic materials for electrochemical applications.