Browsing by Author "Ramirez, Oscar"

Now showing 1 - 11 of 11
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    A novel environmentally friendly method in solid phase for in situ synthesis of chitosan-gold bionanocomposites with catalytic applications
    (2019) Bonardd Salvador, Sebastián Ignacio; Saldías, César; Ramirez, Oscar; Radić Foschino, Deodato D.; Recio Cortés, Francisco Javier; Urzúa, Marcela; Leiva Campusano, Ángel
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    Bimetallic NiPt nanoparticles-enhanced catalyst supported on alginate-based biohydrogels for sustainable hydrogen production
    (2023) Ramirez, Oscar; Bonardd, Sebastian; Saldias, Cesar; Kroff, Macarena; O'Shea, James N.; Diaz, David Diaz; Leiva, Angel
    Alginate hydrogel beads were loaded with bimetallic NiPt nanoparticles by in situ reduction of the respective polymer matrix containing precursor metallic ions using a NaBH4 aqueous solution. The alginate hydrogel beads loaded with NiPt nanoparticles were characterized by TEM, AAS, FT-IR, TGA, XPS, and oscillatory rheometry. The prepared hybrid hydrogels were proven to be effective as catalytic materials for the hydrolysis of ammonia borane (AB) for quantitative hydrogen generation using catalytic loadings of 0.1 mol%. In addition, the reaction mechanism of the hydrolytic reaction using NiPt loaded alginate hydrogel beads was determined by Langmuir-Hinshelwood model. The experimental results showed that the reaction mechanism consisted of an initial fast adsorption of reactants at the surface of the nanoparticles, followed by a rate-limiting surface reaction. The NiPt nanoalloys exhibited an enhanced behavior for hydrogen generation with a maximum TOF of 84.1 min-1, almost 71 % higher compared to monometallic platinum atoms, and likely related to a synergistic interaction between both metals. Finally, the hydrogel matrix enabled the material to be easily recovered from the reaction medium and reused in further catalytic cycles without desorption of active nanoparticles from the material.
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    CuAu bimetallic plasmonic-enhanced catalysts supported on alginate biohydrogels
    (2022) Ramirez, Oscar; Bonardd, Sebastian; Saldias, Cesar; Zambrano, Yadira; Diaz Diaz, David; Leiva, Angel
    We describe the synthesis, characterization and catalytic properties of a series of hybrid materials composed of inorganic plasmonic mono-and bimetallic nanoparticles supported on organic bio-based hydrogel beads. The bimetallic materials showed a localized surface plasmon resonance in the visible region, with a maximum light absorption correlated to the metal composition of the alloyed systems. Thermogravimetric analysis revealed a total water content near to 90 % w/w, which was in good agreement with the free-volume calculated from mu CT scan reconstruction of lyophilized samples. Catalytic essays for the reduction of 4-nitrophenol demonstrated that alginate beads loaded with bimetallic nanoparticles exhibit a 5.4-fold higher apparent kinetic constant (k(app)) than its monometallic counterparts. Additionally, taking advantage of the plasmonic properties given by the nanoparticles is that the materials were tested as photocatalysts. The activity of the catalysts was enhanced by near 2.2 times higher in comparison with its performance in dark conditions.
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    Effects of the Solvent Vapor Exposure on the Optical Properties and Photocatalytic Behavior of Cellulose Acetate/Perylene Free-Standing Films
    (2023) Coderch, Gustavo; Cordoba, Alexander; Ramirez, Oscar; Bonardd, Sebastian; Leiva, Angel; Haering, Marleen; Diaz, David Diaz; Saldias, Cesar
    The search to deliver added value to industrialized biobased materials, such as cellulose derivatives, is a relevant aspect in the scientific, technological and innovation fields at present. To address these aspects, films of cellulose acetate (CA) and a perylene derivative (Pr) were fabricated using a solution-casting method with two different compositions. Consequently, these samples were exposed to dimethylformamide (DMF) solvent vapors so that its influence on the optical, wettability, and topographical properties of the films could be examined. The results demonstrated that solvent vapor could induce the apparent total or partial preferential orientation/migration of Pr toward the polymer-air interface. In addition, photocatalytic activities of the non-exposed and DMF vapor-exposed films against the degradation of methylene blue (MB) in an aqueous medium using light-emitting diode visible light irradiation were comparatively investigated. Apparently, the observed improvement in the performance of these materials in the MB photodegradation process is closely linked to the treatment with solvent vapor. Results from this study have allowed us to propose the fabrication and use of the improved photoactivity "all-organic" materials for potential applications in dye photodegradation in aqueous media.
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    Highly efficient and reusable CuAu nanoparticles supported on crosslinked chitosan hydrogels as a plasmonic catalyst for nitroarene reduction
    (2024) Ramirez, Oscar; Bonardd, Sebastian; Saldias, Cesar; Leiva, Angel; Diaz, David Diaz
    The synthesis of CuAu-based monometallic (MNPs) and bimetallic nanoparticles (BNPs) supported on chitosanbased hydrogels for their application as catalysts is presented. The hydrogels consisted of chitosan chains crosslinked with tripolyphosphate (TPP) in the form of beads with an approximate average diameter of 1.81 mm. The MNPs and BNPs were obtained by the adsorption of metallic ions and their subsequent reduction with hydrazine, achieving a metallic loading of 0.297 mmol per gram of dry sample, with average nanoparticle sizes that were found between 2.6 and 4.4 nm. Both processes, metal adsorption and the stabilization of the nanoparticles, are mainly attributed to the participation of chitosan hydroxyl, amine and amide functional groups. The materials revealed important absorption bands in the visible region of the light spectra, specifically between 520 and 590 nm, mainly attributed to LSPR given the nature of the MNPs and BNPs inside the hydrogels. Subsequently, the hydrogels were evaluated as catalysts against the reduction of 4-nitrophenol (4NP) into 4-aminophenol (4AP), followed by UV-visible spectroscopy. The kinetic advance of the reaction revealed important improvements in the catalytic activity of the materials by synergistic effect of BNPs and plasmonic enhancement under visible light irradiation, given the combination of metals and the light harvesting properties of the nanocomposites. Finally, the catalytic performance of hydrogels containing BNPs CuAu 3:1 showed an important selectivity, recyclability and reusability performance, due to the relevant interaction of the BNPs with the chitosan matrix, highlighting the potential of this nanocomposite as an effective catalyst, with a potential environmental application.
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    Hydrogel composites based on chitosan and CuAuTiO2 photocatalysts for hydrogen production under simulated sunlight irradiation
    (2024) Ramirez, Oscar; Lopez-Frances, Anton; Baldovi, Herme G.; Saldias, Cesar; Navalon, Sergio; Leiva, Angel; Diaz, David Diaz
    This study explored the photocatalytic hydrogen evolution reaction (HER) using novel biohydrogel composites comprising chitosan, and a photocatalyst consisting in TiO2 P25 decorated with Au and/or Cu mono- and bimetallic nanoparticles (NPs) to boost its optical and catalytic properties. Low loads of Cu and Au (1 mol%) were incorporated onto TiO2 via a green photodeposition methodology. Characterization techniques confirmed the incorporation of decoration metals as well as improvements in the light absorption properties in the visible light interval (lambda > 390 nm) and electron transfer capability of the semiconductors. Thereafter, Au and/or Cu NP- supported TiO2 were incorporated into chitosan-based physically crosslinked hydrogels revealing significant interactions between chitosan functional groups (hydroxyls, amines and amides) with the NPs to ensure its encapsulation. These materials were evaluated as photocatalysts for the HER using water and methanol mixtures under simulated sunlight and visible light irradiation. Sample CuAuTiO2/ChTPP exhibited a maximum hydrogen generation of 1790 mu mol g(-1) h(-1) under simulated sunlight irradiation, almost 12-folds higher compared with TiO2/ChTPP. Also, the nanocomposites revealed a similar tendency under visible light with a maximum hydrogen production of 590 mu mol g(-1) h(-1) . These results agree with the efficiency of photoinduced charge separation revealed by transient photocurrent and EIS.
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    Marrying plasmonic earth-abundant metals with catalytic metals for visible-light-promoted hydrogen generation on biobased materials
    (2023) Ramirez, Oscar; Castillo, Sebastian; Bonardd, Sebastian; Saldias, Cesar; O'Shea, James N.; Clive, Christopher Philip; Diaz, David Diaz; Leiva, Angel
    Bimetallic CuPt alloyed nanoparticles were conveniently synthesized on biohydrogels and were capable of carrying out hydrogen release from ammonium borane hydrolysis. The biohydrogel consisted of bead-shaped alginate chains crosslinked by calcium ions, which were used as support material to synthesize and stabilize the bimetallic nanoparticles, employing adsorption and coreduction strategy steps. The as-prepared nanoparticles exhibited light absorption in the visible range (580 nm) resulting from the surface plasmon resonance (SPR) phenomenon ascribed to the presence of copper in the alloyed system. On the other hand, the presence of platinum atoms in these nanoalloys endows them with a notable catalytic performance toward ammonia borane hydrolysis as a hydrogen release reaction, reaching kr values from 0.32 x 10-4 to 2.23 x 10-4 mol L-1 min-1 as the Pt content increases. Finally, by taking advantage of the SPR light absorption shown by CuPt 1:1, it was demonstrated that these entities could be successfully employed as photocatalysts for the hydrogen generation reaction, boosting its activity by almost 2.06 times compared to its performance in dark conditions. This catalytic enhancement was mainly ascribed to the light-harvesting properties promoted by plasmonic effects and the specimen's metallic composition.
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    New Hybrid Nanocomposites with Catalytic Properties Obtained by In Situ Preparation of Gold Nanoparticles on Poly (Ionic Liquid)/Poly (4-Vinylpyridine) Nanofibers
    (2022) Ramirez, Oscar; Leal, Matias; Briones, Ximena; Urzua, Marcela; Bonardd, Sebastian; Saldias, Cesar; Leiva, Angel
    In this work, we report the obtaining of new hybrid nanocomposites with catalytic activity formed by nanofibers of polymer blends and gold nanoparticles. The nanofibers were obtained by electrospinning blends of a poly (ionic liquid) (PIL) and its precursor polymer, poly (4-vinyl pyridine) (P4VPy). The characteristics of the nanofibers obtained proved to be dependent on the proportion of polymer in the blends. The nanofibers obtained were used to synthesize, in situ, gold nanoparticles on their surface by two-step procedure. Firstly, the adsorption of precursor ions on the nanofibers and then their reduction with sodium borohydride to generate gold nanoparticles. The results indicated a significant improvement in the performance of PIL-containing nanofibers over pure P4VPy NFs during ion adsorption, reaching a 20% increase in the amount of adsorbed ions and a 6-fold increase in the respective adsorption constant. The catalytic performance of the obtained hybrid systems in the reduction reaction of 4-nitrophenol to 4-aminophenol was studied. Higher catalytic conversions were obtained using the hybrid nanofibers containing PIL and gold nanoparticles achieving a maximum conversion rate of 98%. Remarkably, the highest value of kinetic constant was obtained for the nanofibers with the highest PIL content.
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    Poly(ionic liquid)-Based Hydrogel for Emerging Pollutant Removal and Controlled Drug Delivery
    (2024) Ramirez, Oscar; Castillo, Sebastian; Bonardd, Sebastian; Saldias, Cesar; Diaz, David Diaz; Leiva, Angel
    In this study, we report the synthesis and characterization of a set of poly(ionic liquid) (PIL)-based gel membranes formed by the reaction of poly(4-vinylpyridine) (P4VPy) with a terminal dibrominated poly(ethylene glycol) (PEG), which led to the formation of quaternized pyridines as cross-linking joints. First, for hydrogel synthesis, PEG terminal hydroxyls were brominated and subsequently reacted with P4VPy, resulting in the formation of ionic liquid (IL)-like moieties within the hydrogel network. Modified PEG and PIL-based membranes were characterized by Nuclear Magnetic Resonance (NMR), Fourier-Transform Infrared (FT-IR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC), as well as their swelling and adsorption properties. FT-IR spectroscopy confirmed the quaternization of the pyridine pendant groups of P4VPy by the appearance of a band at 1639 cm-1 due to the presence of pyridinium units. Thermal characterization revealed a decrease in the thermal stability of the membranes with respect to the starting materials, probably ascribed to the presence of charged species inside the cross-linked matrix. Furthermore, DSC characterization revealed that the P4VPy:PEG ratio and degree of cross-linking strongly affected the amount of non-freezable water. Swelling experiments of the hydrogels revealed a swelling ratio value (% SW) near 297% after 2 h of hydration, showing remarkable recyclability over multiple hydration and drying cycles. Finally, sodium diclofenac (DCl) and methyl orange (MO) adsorption experiments revealed the remarkable ability of the hydrogels to remove pollutants from water, with q max values of 166.7 and 218.8 mg/g, respectively. Finally, a hydrogel loaded with DCl was used as a model system for drug release experiments, in which the hydrogel was able to release almost 70% of DCl to the medium within 1 day of exposure. This process is controlled mainly by a polymer relaxation mechanism and influenced by the temperature of the experiment, showing great potential for reuse in further experiments and also as an interesting platform for controlled drug release.
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    Porous chitosan-based nanocomposites containing gold nanoparticles. Increasing the catalytic performance through film porosity
    (2022) Bonardd, Sebastian; Ramirez, Oscar; Abarca, Gabriel; Leiva, Angel; Saldias, Cesar; Diaz, David Diaz
    The preparation of porous and non-porous chitosan thin-films containing gold nanoparticles was carried out, aiming to evaluate the effect of porosity on their catalytic response using the p-nitrophenol reduction as model reaction. To achieve this, both types of samples were decorated with gold nanoparticles having similar characteristics in terms of amount, size and shape, which were synthesized following a two-step adsorption-reduction process. The results demonstrated that the presence of porosity generates a considerable enhancement of the catalytic property. This behavior is reflected in higher kinetic constant and conversion values, along with a better recyclability after consecutive cycles. The inclusion of porosity in nanocomposites afforded kobs values 7.5 times higher than the non-porous material, as well as conversion values as high as 80 % in <20 min. On the other hand, as an additional experiment, a porous sample prepared with half the amount of gold also exhibited a better performance than the non-porous catalyst, revealing that the porosity allowed to decrease the amount of catalytic metal used and still exhibiting kobs values 5.9 times higher than the non-porous specimen. These studies demonstrate that there is an important synergistic support-nanostructure relationship, which strongly influences the performance of the nanomaterial.
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    Unlocking the potential of Opuntia species mucilage in chemistry
    (2024) Martin, Cristina del Mar Garcia; Ramirez, Oscar; Bonardd, Sebastian; Lopez-Darias, Marta; Franco, Lourdes; 'Rabet, Yassine M.; Khwaldia, Khaoula; Diaz, David Diaz
    Herein, we describe a detailed protocol to extract the mucilage from different species of the genus Opuntia spp. (i. e., Opuntia Ficus (OFi), Opuntia Dillenii (ODi) and Opuntia Robusta (ORo)). The extracted mucilage was characterized by NMR, FTIR-ATR, HPLC, and TGA. OFi was found to have the highest phenolic content, 7.84 +/- 1.93 mg catechol/g mucilage. The mucilage from the three species were characterized by having a high content of monosaccharides, being mannose and glucose the most abundant components (ca. 48-73 % and 23-35 %, respectively). In the context of biomass revalorization, the mucilage was proven to serve as a reducing and stabilizing agent in the synthesis of gold nanoparticles (AuNP/mucilage). The synthesis was optimized with a mucilage concentration of 2 mg/mL using 12.5 mu L of KAuCl4 and was carried out at 80 degrees C for 90 min. This protocol afforded spherical nanoparticles with an average size of 9.7 +/- 4.0 nm that were stable for at least 14 days, as demonstrated by TEM. Synthesized AuNP/mucilage was evaluated as a plasmonic catalyst for the reduction of 4-nitrophenol as model reaction, showing a considerable enhancement in its kapp of 97 % under white light and a decrease of 24.8 % in its activation energy.