Hamad, Said

Profesor/a Titular de Universidad
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First Name
Last Name
Universidad Pablo de Olavide
Sistemas Físicos, Químicos y Naturales
Research Center
Química Física
Research Group
Química Física de Fases Condensadas e Interfases
Física, Química y Matemáticas
PhD programs
Simulación Molecular de Sistemas Complejos con Aplicaciones Medioambientales, Tecnología Química y de Materialea
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Now showing 1 - 5 of 5
  • Publication
    Role of Ionic Liquid [EMIM]+[SCN]− in the Adsorption and Diffusion of Gases in Metal–Organic Frameworks
    (American Chemical Society, 2018-08-08) Vicent Luna, José Manuel; Gutiérrez Sevillano, Juan José; Hamad, Said; Anta, Juan; Calero, Sofía
    We study the adsorption performance of metal−organic frameworks (MOFs) impregnated of ionic liquids (ILs). To this aim we calculated adsorption and diffusion of light gases (CO2, CH4, N2) and their mixtures in hybrid composites using molecular simulations. The hybrid composites consist of 1-ethyl-3-methylimidazolium thiocyanate impregnated in IRMOF-1, HMOF-1, MIL-47, and MOF-1. We found that the increase of the amount of IL enhances the adsorption selectivity in favor of carbon dioxide for the mixtures CO2/CH4 and CO2/N2 and in favor of methane in the mixture CH4/N2. We also provide detailed analysis of the microscopic organization of ILs and adsorbates via radial distribution functions and average occupation profiles and study the impact of the ILs in the diffusion of the adsorbates inside the pores of the MOFs. Based on our findings, we discuss the advantages of using IL/MOF composites for gas adsorption to increase the adsorption of gases and to control the pore sizes of the structures to foster selective adsorption.
  • Publication
    Critical Role of Dynamic Flexibility in Ge-Containing Zeolites: Impact on Diffusion
    (Wiley, 2016-06-15) Gutiérrez Sevillano, Juan José; Calero, Sofía; Hamad, Said; Grau-Crespo, Ricardo; Rey, Fernando; Valencia, Susana; Palomino, Miguel; Rodríguez Gómez, Salvador; Ruiz-Salvador, A. Rabdel
    static flexibility to their framework, by stabilizing the formation of small rings. In this work, we show that the flexibility associated to Ge atoms in zeolites goes beyond this static effect, manifesting also a clear dynamic nature, in the sense that it leads to enhanced molecular diffusion. Our study combines experimental and theoretical methods providing evidence for this non-previously described effect, as well as a rationalization for it, based on atomistic grounds. We have used both pure-silica and silico-germanate ITQ-29 (LTA topology) zeolites as a case of study. Based on our simulations, we identify the flexibility associated to the pore breathing-like behavior induced by the Ge atoms, as the key factor leading to the enhanced diffusion observed experimentally in Ge-containing zeolites
  • Publication
    Adsorption of hydrogen sulphide on Metal-Organic Frameworks
    (Royal Society of Chemistry, 2013-04-18) Gutiérrez Sevillano, Juan José; Martin Calvo, Ana; Dubbeldam, David; Calero, Sofía; Hamad, Said
    Three new sets of interatomic potentials to model hydrogen sulphide (H2S) have been fitted. One of them is a 3-sites potential (which we named 3S) and the other two are 5-sites potentials (which we named 5S and 5Sd). The molecular dipole of the 3S and 5S potentials is 1.43 D, which is the value usually employed for H2S potentials, while the dipole of the 5Sd is the dipole measured experimentally for the H2S molecule, circa 0.974 D. The interatomic potentials parameters were obtained by fitting the experimental vapourliquid equilibrium, vapour pressure and liquid density curves. The potential parameters fitted so far for H2S have been obtained applying long-range corrections to the Lennard–Jones energy. For that reason, when a cut and shift of the Lennard–Jones potentials is applied they do not yield the correct results. We employed a cut and shift of the Lennard–Jones potentials in the fitting procedure, which facilitates the use of the new potentials to model H2S adsorption on systems such as Metal-Organics Frameworks (MOFs). We have employed the newly developed potentials to study the adsorption of H2S on Cu-BTC, MIL-47 and IRMOF-1 and the results agree with the available electronic structures calculations. All calculations (both quantum and interatomic potential-based) predict that H2S does not bind to the Cu atoms in Cu-BTC.
  • Publication
    Toward a Transferable Set of Charges to Model Zeolitic Imidazolate Frameworks: Combined Experimental–Theoretical Research
    (American Chemical Society, 2012-12-10) Gutiérrez Sevillano, Juan José; Calero, Sofía; Ania, Conchi O.; Parra, José B.; Kapteijn, Freek; Gascon, Jorge; Hamad, Said
    In a combined experimental and theoretical study, the first transferable set of charges of imidazolate linkers has been derived specifically to model zeolitic imidazolate frameworks (ZIFs). The validity of the charges is demonstrated by comparing experimental and computed results of CH4 and CO2 adsorption on ZIF-7, ZIF-8, ZIF-69, and ZIF-71. The sets of charges obtained with this method provide values of isosteric heats of adsorption and adsorption isotherms of similar accuracy as those obtained using specific sets of charges derived for each individual structure, with the great advantage of being readily transferable to a wide range of ZIFs.
  • Publication
    Comparing gas separation performance between all known zeolites and their zeolitic imidazolate framework counterparts
    (Royal Society of Chemistry (UK), 2015-11-10) Gómez-Álvarez, P.; Hamad, Said; Haranczyk, M.; Ruiz-Salvador, A. Rabdel; Calero, S.
    To find optimal porous materials for adsorption-based separations is a challenging task due to the extremely large number of possible pore topologies and compositions. New porous material classes such as Metal Organic Frameworks (MOFs) are emerging, and hope to replace traditionally used materials such as zeolites. Computational screening offers relatively fast searching for candidate structures as well as side-by-side comparisons between material families. This work is pioneering at examining the families comprised by the experimentally known zeolites and their respective Zeolitic Imidazolate Framework (ZIF) counterparts in the context of a number of environmental and industrial separations involving carbon dioxide, nitrogen, methane, oxygen, and argon. Additionally, unlike related published work, here all the targeted structures have been previously relaxed through energy minimization. On the first level of characterization, we considered a detailed pore characterization, identifying 24 zeolites as promising candidates for gas separation based on adsorbate sizes. The second level involved interatomic potential-based calculations to assess the adsorption performance of the materials. We found no correlation in the values of heat of adsorption between zeolites and ZIFs sharing the same topology. A number of structures were identified as potential experimental targets for CO2/N2, and CO2/CH4 affinity-based separations.