Browsing by Author "Diaz-Droguett, D. E."

Now showing 1 - 4 of 4
  • No Thumbnail Available
    Item
    Chemical and structural analysis related to defects in nanocrystalline Ba1-xSrxTiO3 grown via hydrothermal sol-gel
    (2014) Fuentes, S.; Cespedes, F.; Padilla-Campos, L.; Diaz-Droguett, D. E.
    The chemical and structural properties of Ba1-xSrxTiO3 (BST, x=0-1) nanoparticles synthesised via sol-gel-hydrothermal were analysed. Two types of salts of Ba (BaCl2 and Ba(OH)(2)) and Sr (SrCl2 and Sr(OH)(2)) as starting reactants were used to compare two synthesis methods. Chemical characterisation and oxidation states were obtained using X-ray photoelectron spectroscopy. Structural information was acquired by Raman spectroscopy, and calculations to obtain theoretical Raman spectra associated with the different formed phases of BST were performed for comparison. The results were consistent with the presence of oxygen vacancies in all of the compounds synthesised, but the use of hydroxide salts introduced a minor concentration of oxygen vacancies into the BST compounds. In addition, the presence of oxygen vacancies produced an increase of the intensity of first-order modes of vibration and a minor oxidation state of the Ti atom in the structure. Finally, the oxygen vacancies produced a distortion of the structure, inducing the existence of the non-perovskite phase. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
  • No Thumbnail Available
    Item
    Enhanced hydrogen adsorption properties of mesoporous nano-TiO2@SnO2
    (2023) Rajendran, Saravanan; Gnanasekaran, Lalitha; Hoang, Tuan K. A.; Diaz-Droguett, D. E.; Gracia, F.; Gracia-Pinilla, M. A.
    Today, hydrogen as being one of the most advantageous energy supplies for various applications and specifically not with carbon emissions, alluring strategies are made possible for its production and storage. Since the metal oxides (MOs) semiconductors give rise to the development of new technologies related to renewable energy and environmental issues, this work is envisioned to study the hydrogen adsorption properties of TiO2@SnO2 catalyst synthesized via novel approach by integrating sol-gel and thermal decomposition methods. The synthesized TiO2 and its composite have been analyzed by sophisticated instruments to reveal the drastic enhancement of hydrogen adsorption. In this work, hydrogen measurements were accomplished by quartz crystal (QC) microbalance method. The Raman scattering experiment of the composite revealed the lower peak intensity compared with pure TiO2, which demonstrated the surface defects that created oxygen vacancies with reduced oxidation states of the metal centers. Meanwhile, the mesoporous nanostructure of TiO2@SnO2 could be confirmed via High resolution transmission electron (HR-TEM) microscopic analysis. Besides, the intermediate states of the composite were analyzed through Photoluminescence (PL) spectra which demonstrated the delay in recombining charges. The Barrett-Joyner- Halenda (BJH) method illustrated the larger pore size and pore volume with decreased surface area of the composite. The addition of SnO2 into TiO2 has reported 4 times greater the adsorption of pristine TiO2 particles, because of the capacity of SnO2 to hinder pores. Moreover, the titania oxidation states play a predominant role in the procurement of larger H2 adsorption. Also, the Ti4+ and Sn4+ reveal fragile Kubas type of adsorption that facilitated the hydrogen storage.
  • No Thumbnail Available
    Item
    Gas effects on the chemical and structural characeristics of porous MoO3 and MoO3-x grown by vapor condensation in helium and hydrogen
    (2011) Diaz-Droguett, D. E.; Fuenzalida, V. M.
    Porous MoO3 and MoO3-x were grown in vapor-phase under He and H-2 at pressures between 100 and 1200 Pa. MoO3 was vaporized from a tungsten boat heated between 650 and 1250 degrees C. Growth of porous material was promoted at 100 and 200 Pa of the carrier gas. At higher pressures and only in hydrogen under particular preparation conditions, samples rich in porous phase were formed. Samples grown either in helium or in hydrogen have similar aspect under SEM, TEM and XRD, but important differences were detected with thermogravimetry and Raman spectroscopy. The thermogravimetric analysis revealed a hydrated compound in the H-2-grown samples produced at 100 Pa, whereas a non-hydrated compound grew under helium under the same preparation conditions. The Raman spectra revealed some vibrational modes of beta-MoO3 for the He-grown samples at 100 Pa, whereas alpha-MoO3 was only revealed for the H-2-grown samples grown at the same pressure. The effect of the hydrogen pressure on the oxidation state of the porous samples was studied, showing the existence Mo5+ in the porous samples grown at 600 Pa, whereas the samples grown under a lower pressure exhibit the same chemical composition of the source material. The growth kinetics of the porous samples is discussed under different gases as well as the effect of the gas on the chemical and structural characteristics of the samples. (C) 2010 Elsevier B.V. All rights reserved.
  • No Thumbnail Available
    Item
    Structural, optoelectronic and photo-thermoelectric properties of crystalline alloy CuAlxFe1-xO2 delafossite oxide materials
    (2021) Wheatley, R. A.; Roble, M.; Gence, L.; Acuna, C.; Rojas-Aedo, R.; Hidalgo-Rojas, D.; Guzman-De La Cerda, D. E.; Vojkovic, S.; Seifert, B.; Wallentowitz, S.; Volkmann, U. G.; Diaz-Droguett, D. E.
    CuFeO2 and CuAlO2 are attractive candidate materials for solar energy harvesting applications such as photocatalysis and photovoltaics. This work describes the structural, optoelectronic, thermal and electric properties of alloyed CuAlxFe1-xO2 Delafossite material synthesized using solid-state sintering techniques. The alloyed samples of CuAlxFe1-xO2 Delafossite oxide consisted of substitution of Fe for Al ranging from x = 0.01 to x = 0.99. The inclusion of Al in low concentrations affects the crystallization rate during solid-state synthesis, dramatically changing the resultant sample morphologies. The addition of dilute amounts of Al also greatly improves the conductivity of the material to a maximum of 3.18 Scm(-1). The material absorption edge shows strong changes over the alloying range. The more highly conducting samples show a strong photoinduced thermoelectric response to Vis-NIR illumination. (C) 2020 Published by Elsevier B.V.