Examinando por Autor "Valenzuela, M.L."

Mostrando 1 - 3 de 3
  • Miniatura
    Ítem
    Electroanalytical analysis of glassy carbon electrode modified with COOH- and NO2-functionalized polyspyrophosphazenes
    (Sociedad Chilena de Química, 2017) Valenzuela, M.L.; Cisternas, R.; Jara-Ulloa, P.; Rodriguez, L.
    Glassy carbon electrode modified with COOH- and NO2-functionalized polyspyrophosphazenes were used to study the redox process of a electroactive probe (ferrocene) in non-aqueous electrolyte. The electrochemical behavior of polyphosphazenes substituted with COOH and NO2 groups has been studied using cyclic voltammetry. Their blocking properties depend on the substituent group and on the substitution/nitration degree. The oxoreduction of the couple Fc/Fc+ occurs with rapid redox kinetic at the modified glassy carbon electrode with high nitration degree NO2-functionalized polyspyrophosphazene. The polymers were immobilized on the glassy carbon surface at different concentrations to study surface charge density effect. In this report were studied the reproducibility, repeatability and stability of the modified electrodes.
  • Miniatura
    Ítem
    Incorporation of nio into sio2, tio2, al2o3, and na4.2ca2.8(si6o18) matrices: Medium effect on the optical properties and catalytic degradation of methylene blue
    (MDPI AG, 2020-12) Diaz, C.; Valenzuela, M.L.; Cifuentes-Vaca, O.; Segovia, M.; Laguna-Bercero, M.A.
    The medium effect of the optical and catalytic degradation of methylene blue was studied in the NiO/SiO2, NiO/TiO2, NiO/Al2O3, and NiO/Na4.2Ca2.8(Si6O18) composites, which were prepared by a solid-state method. The new composites were characterized by XRD (X-ray diffraction of powder), SEM/EDS, TEM, and HR-TEM. The size of the NiO nanoparticles obtained from the PSP-4-PVP (polyvinylpyrrolidone) precursors inside the different matrices follow the order of SiO2 > TiO2 > Al2O3 . However, NiO nanoparticles obtained from the chitosan precursor does not present an effect on the particle size. It was found that the medium effect of the matrices (SiO2, TiO2, Al2O3, and Na4.2Ca2.8(Si6O18)) on the photocatalytic methylene blue degradation, can be described as a specific interaction of the NiO material acting as a semiconductor with the MxOy materials through a possible p-n junction. The highest catalytic activity was found for the TiO2 and glass composites where a favorable p-n junction was formed. The isolating character of Al2O3 and SiO2 and their non-semiconductor behavior preclude this interaction to form a p-n junction, and thus a lower catalytic activity. NiO/SiO2 and NiO/Na4.2Ca2.8(Si6O18) showed a similar photocatalytic behavior. On the other hand, the effect of the matrix on the optical properties for the NiO/SiO2, NiO/TiO2, NiO/Al2O3, and NiO/Na4.2Ca2.8(Si6O18) composites can be described by the different dielectric constants of the SiO2, TiO2, Al2O3, Na4.2Ca2.8(Si6O18) matrices. The maxima absorption of the composites (λmax) exhibit a direct relationship with the dielectric constants, while their semiconductor bandgap (Eg) present an inverse relationship with the dielectric constants. A direct relationship between λmax and Eg was found from these correlations. The effect of the polymer precursor on the particle size can explain some deviations from this relationship, as the correlation between the particle size and absorption is well known. Finally, the NiO/Na4.2Ca2.8(Si6O18) composite was reported in this work for the first time. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
  • Miniatura
    Ítem
    Sorption of apolar pesticides by units of benzoic acid propyl ester in cyclic phosphazene
    (Sociedad Chilena de Quimica, 2017) Rivas, J.; Valenzuela, M.L.
    The effects of temperature, pH and agitation time (equilibrium) on the adsorption process of different pesticides on N3P3(OC6H4COOCH2CH2CH3)6 was studied. With optimal conditions experimental, the adsorption isotherms have been realized with through Langmuir and Freundlich models. Pesticides are compounds used mainly in agriculture to control various species (plants, insects, worms, fungi). Due to their physicochemical properties, they can remain for a long time in the application sites, bioaccumulating and moving between environmental compartments which generate various environmental problems. The results obtained showed a physisorption mechanism for the fve pesticides studied, with higher sorption for: azinphos methyl (93,5 mg kg-1), carbaryl (290.5 mg kg-1) and carbofuran (580.5 mg kg-1) at 20 ° C, according to the models used. © 2018 Sociedad Chilena de Quimica. All rights reserved.