Browsing by Author "Segura, Rodrigo"

Now showing 1 - 5 of 5
  • No Thumbnail Available
    Item
    Condensed tannins from Pinus radiata bark: Extraction and their nanoparticles preparation in water by green method
    (2024) Cabrera-Barjas, Gustavo; Butto-Miranda, Nicole; Nesic, Aleksandra; Moncada-Basualto, Mauricio; Segura, Rodrigo; Bravo-Arrepol, Gaston; Escobar-Avello, Danilo; Moeini, Arash; Riquelme, Sebastian; Neira-Carrillo, Andronico
    This work reports for the first time the production of condensed tannin nanoparticles stable in water via modification with glycine betaine. Pine bark, as a byproduct from the paper industry, was used as a source of condensed tannins of high molecular weight. Different glycine betaine concentrations were tested to produce condensed tannin nanoparticles, and the obtained nanoparticles were subjected to several characterization techniques (Dynamic Light Scattering, Field emission scanning electron microscopy, Zeta potential, Fourier transform infrared spectroscopy-Attenuated total reflectance, thermogravimetric analysis). The results showed that the highest stability possessed nanoparticles with 40 wt% glycine betaine. The average particle size distribution evaluated by scanning microscopy was 124 nm. Besides, the glycine betaine-modified condensed tannin nanoparticles demonstrated higher thermal stability with the starting degradation temperature at 238 degrees C. Finally, obtained nanoparticles showed an antioxidant capacity of 34,209 +/- 2194 mu mol ET/100 g and low cytotoxicity towards healthy human cells, representing the high potential to be used as a carrier of active compounds in agriculture, food, drug and medical sector.
  • No Thumbnail Available
    Item
    Development of a fast and sensitive method for the determination of As(III) at trace levels in urine by differential pulse anodic voltammetry using a simple graphene screen-printed electrode
    (2020) Nunez, Claudia; Jose Trivino, Juan; Segura, Rodrigo; Arancibia, Veronica
    A simple and fast anodic voltammetric method was employed to determine traces of As(III) in urine samples using commercial screen-printed graphene electrodes without subsequent modification. To obtain a sensitive and selective method for As(III) determination, the effects of various parameters such as pH, supporting electrolyte concentration, accumulation potential (E-acc), accumulation time (t(acc)), and potential scan conditions were studied. The optimum experimental conditions were chosen to be as follows: pH of 2.8 (0.01 mol L-1 phosphate buffer), scan increment of 4 mV, pulse width of 80 ms, pulse period of 0.5 s, and pulse amplitude of 200 mV. Differential pulse voltammograms were obtained by scanning from -0.80 V to 0.80 V without applying an accumulation step. Under these conditions, one peak was observed at 0.27 V due to As-0 oxidation. After optimizing the experimental conditions, the anodic peak current for As was found to be linearly related to its concentration up to ca. 5.0 mu g L-1, with detection and quantitation limits (DLs, QLs) of 0.28 mu g L-1 and 0.92 mu g L-1, respectively. The developed method was validated by the determination of As(III) in spiked tap water from our laboratory, which showed an As(III) concentration of 50.64 +/- 0.10 mu g L-1 (spiked with 50.0 mu g L-1); two urine samples (where As was not detected) spiked with As(III) 0.73 mu g L-1 and 0.91 mu g L-1 (in the cell) showed an As(III) concentration of 0.70 mu g L-1 and 0.91 mu g L-1, respectively. The method was successfully applied to the determination of As-total in 16 urine samples obtained from workers occupationally exposed to inorganic arsenic compounds without previous treatment. The results obtained for As-total were compared with measurements made by an external analytical laboratory, which used HG-AAS. To determine As-total, As(V) was reduced in the presence of thiosulfate in an acid medium. The electrode showed good stability and repeatability.
  • No Thumbnail Available
    Item
    Effect of thiol adsorption on the electrical resistance of copper ultrathin films
    (2024) Gray, Gabriel; Marin, Francisca; del Campo, Valeria; Gonzalez-Fuentes, Claudio; Correa-Puerta, Jonathan; Flores, Marcos; Segura, Rodrigo; Haberle, Patricio; Henriquez, Ricardo
    The impact of thiol adsorption on thin copper films, covered with a copper oxide layer, was investigated using electrical resistance measurements at various stages: during film growth, aging, exposure to air, and immersion in thiol solutions. Thin copper films (20 nm) were thermally evaporated, with variations in substrate temperature (RT, 330 and 390 K). Films deposited at 330 K exhibited the smallest percolation thickness and aging rates due to their compact morphology, showcasing lower surface roughness and correlation length. Exposure to air led to the formation of a Cu2O 2 O layer on the film surface. Subsequent immersion in a dodecanethiol solution in ethanol resulted in a resistance increase, ranging from 0.1 % to 0.4 %. This change was dependent on the substrate temperature, with the largest difference observed at 330 K. This observation suggests that samples grown at this temperature exhibited the highest electron-surface scattering. Moreover, by depositing a chromium surfactant layer, the impact of this scattering mechanism was amplified, leading to a resistance increase of up to 1.2 %. Mayadas-Shatzkes theory provided a good description of these resistance changes. The negatively charged S-head of the adsorbed thiols alters the electric field experienced by conduction electrons in the Cu2O/Cu 2 O/Cu interface, modifying the electron-surface scattering.
  • No Thumbnail Available
    Item
    Nafion-mercury coated film electrode for the adsorptive stripping voltammetric determination of lead and cadmium in the presence of pyrogallol red
    (2012) Nagles, Edgar; Arancibia, Veronica; Rojas, Carlos; Segura, Rodrigo
    An adsorptive stripping voltammetric (AdSV) method is presented for the simultaneous determination of Pb(II) and Cd(II) at trace levels in natural waters, based on metal complexation with pyrogallol red (PR) and subsequent adsorptive deposition on a Nation-mercury coated glassy carbon electrode (NHgFE). Pyrogallol red forms complexes with a metal:ligand stoichiometry of 1:1 with Pb(II) and of 1:2 with Cd(II). Optimal analytical conditions were pH 4.0 (acetate buffer); C-PR = 2.8 mu mol L-1; E-ads = -0.40 V vs. Ag/AgCl; t(ads) = 100 s. The linear calibration curves ranged from 1.0 mu g L-1 to 16.0 mu g L-1 for Pb(II) and from 1.0 mu g L-1 to 13.0 mg L-1 for Cd(II). The detection limits (S/N=3) were 0.05 mu g L-1 for Pb(II) and 0.01 mg L-1 for Cd(II). The relative standard deviation was 1.0% and 2.0% (n = 7), respectively, for a solution containing 5.0 mu g L-1 Pb(II) and Cd(II). The method was validated by determining Pb(II) and Cd(II) in certified reference waste water (SPS-WW1). Finally, the method was applied to the determination of Pb(II) and Cd(II) in commercial mineral water samples after UV digestion. (C) 2012 Elsevier B.V. All rights reserved.
  • No Thumbnail Available
    Item
    Spontaneous self-assembly of magnetic nanoparticle chains, at the first stage of a gas aggregation source
    (2024) Orellana, Christian; Gonzalez-Fuentes, Claudio; Abellan, Maria; Segura, Rodrigo; Oyazrun, Simon; Acevedo, Cristian; Romero, Christian
    There is an increasing interest in magnetic nanoparticles (MNPs) and self-assembled MNP chains for applications in biomedicine, catalysis, and other technologically relevant applications. In this work, we report the spontaneous self-assembly of MNPs at the top surface of the shield of a magnetron sputter head. The resulting nanostructures consisted of clustered nanoscale chains arranged in highly oriented microfibers, with lengths of micrometer order and diameters ranging from 20 to 600 nm. The intense magnetic field gradient around the sputter magnetron's head is the driving force of the self-assembly process, also trapping species that would otherwise be lost in the carrier gas flow.