Browsing by Author "David Contreras"

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    Highly efficient hydrogen evolution reaction, plasmon-enhanced by AuNP-l-TiO2NP photocatalysts
    (2020) Judith Castillo-Rodriguez; Pedro D. Ortiz; Mauricio Isaacs; Natalia P. Martinez; James N. O’Shea; Jack Hart; Robert Temperton; Ximena Zarate; David Contreras; Eduardo Schott
    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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    Role of β-CD Macromolecule Anchored to α-Fe2O3/TiO2 on the Selectivity and Partial Oxidation of Guaiacol to Add-Value Products
    (2021) Nicole Espinoza-Villalobos; Susana Rojas; Ricardo Andrés Salazar; David Contreras; Nestor Escalona; Elizabeth Vergara; Miguel Angel Laguna-Bercero; Fernando Mendizabal; Lorena Barrientos
    Biomass is a naturally abundant, sustainable, and clean resource, which has the potential to replace fossil feedstock for sustainable production of high add-value chemicals. However, an efficient conversion process is still difficult to achieve due to the difficult reaction conditions. In this study as a novel and versatile concept, we introduced the use of beta-cyclodextrin (beta-CD) macromolecule to enhance the photocatalytic behavior of a alpha-Fe2O3/TiO2 heterojunction. The selective conversion of guaiacol was evaluated using 0.2, 1.0, and 2.0 molar ratios of beta-CD anchored on 0.7 wt % alpha-Fe2O3/TiO2 under mild reaction conditions. 1.0 molar ratio of beta-CD promoted photo-oxidation of guaiacol to mainly produce p-benzoquinone with similar to 68% selectivity at similar to 10% conversion. To understand this effect, Electron Paramagnetic Resonance Spectroscopy (EPR) in operando mode and Diffuse Reflectance Spectroscopy (DRS) experiments were performed. The results showed that the 1.0 molar ratio of beta-CD decreases the bandgap from 3.06 to 2.76 eV and controls the center dot OH radical concentration due to the formation of a covalent bond between beta-CD and semiconductors. The improved guaiacol adsorption capacity on the photocatalyst resulted in the enhancement of the photochemical activity and selectivity. Additionally, a possible pathway of guaiacol transformation was proposed through the oxidation intermediates. Furthermore, the photocatalyst beta-CD/alpha-Fe2O3/TiO2 can be recycled efficiently and reused three times, without loss in reactivity.