Browsing by Author "Oskam, Gerko"

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    Structural and photoelectrochemical dynamics of in-situ hydrogenated anatase TiO2 thin films grown by DC reactive magnetron sputtering
    (2023) Villarroel, Roberto; Zambrano-Mera, Dario; Espinoza-Gonzalez, Rodrigo; Paredes-Gil, Katherine; Pantaleone, Stefano; Ballesteros, Luis; Oskam, Gerko; Garcia-Merino, Jose A.; Hevia, Samuel A.; Gonzalez-Moraga, Guillermo
    Hydrogenation has become one of the most used strategies to improve the photoactive properties of titanium dioxide nanomaterials, n-TiO2. In order to obtain more information about the hydrogenated process on anatase TiO2 thin films and the improvement of the photoactivity of this material, we report a study on the structural changes of hydrogenated anatase thin films produced by direct-current reactive magnetron sputtering. In the first stage of the hydrogenation process, the obtained polycrystalline anatase films present an increment of the {0 0 1} facet according to the amount of hydrogen used in the plasma reaction. At higher hydrogen concentrations, amorphous and rutile phases start to appear. The photoactivity of the hydrogenated anatase samples, H:TiO2, presents a redshift of the photoelectrochemical onset and an increase of the reactivity in the UV region. Both results were experimentally and theoretically related to the formation of defects such as oxygen vacancies and TiH/Ti-OH bonds at the surface of the hydrogenated thin films.
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    The effect of oxidative functionalization of carbon nanotubes on the morphological, optical, and photoelectrochemical properties of modified titanium dioxide photoanodes
    (2023) Peon-Diaz, Francisco J.; Segura del Rio, Rodrigo; Hevia, Samuel; Olivares, Fernanda; Carlos Exposito-Galvez, Juan; Escalante, Renan; Valadez-Villalobos, Karen; Riquelme, Antonio J.; Oskam, Gerko; Henriquez, Ricardo
    In this work, we demonstrate the influence of the oxidative treatment of carbon nanotubes (CNTs) on the morphological, optical, and photoelectrochemical properties of CNTs-TiO2 photoanodes. CNTs were synthesized by a chemical vapor deposition method (CVD) and subsequently oxidized in a mixture of HNO3/H2SO4 to introduce nitrogen- and oxygen-containing functional groups. The oxidation time was varied (45, 90, and 180 min) to obtain CNTs with different oxidation levels (CNTs-ox). Pristine and oxidized CNTs were deposited on ITO and used as substrates to fabricate ITO/CNTs/TiO2 photoelectrodes by depositing a TiO2 thin layer using a CVD procedure. The extent of oxidation of the CNTs was found to directly influence the homogeneity and morphology of the TiO2 overlayer, its physical stability, and the optical and photoelectrochemical properties of the photoelectrodes. An optimum oxidative treatment was achieved for 90 min, leading to a CNTs-ox/TiO2 electrode with the best performance. Compared to shorter and longer times, this sample showed the smallest bandgap and the best homogeneity of TiO2 growth on the CNTs' surface. Optimal photoelectrochemical performance was also found for this sample (160 mu A/cm(2) at 0 V vs. Ag/AgCl) in KCl (0.1 M) electrolyte (100 mW/cm(2), Xenon arc lamp).