Calero, Sofía

Catedrático/a 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
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Now showing 1 - 10 of 23
  • Publication
    Molecular Sieves for the Separation of Hydrogen Isotopes
    (American Chemical Society, 2019) Pérez Carbajo, Julio; Parra, José B; Ania, Conchi O; Merkling, Patrick; Calero, Sofía
    Stable molecular hydrogen isotopes, D2 and T2, are both scarce and essential in several energy, industrial, and large-scale fundamental research applications. Due to the chemical similarity of these isotopes, their extraction and purification from hydrogen has relied for decades on expensive and energy-demanding processes. However, factoring in the phenomenon of quantum sieving could provide a new route for these separations. In this work, we have explored how to separate hydrogen isotopes by adsorption taking these quantum effects into account. To this end, we have conducted adsorption measurements to test our deuterium model and performed a widespread computational screening over 210 pure-silica zeolites for D2/H2 and T2/H2 separations. Based on low-coverage adsorption properties, a reduced set of zeolites have been singled out and their performance in terms of adsorption capacity, selectivity, and dynamic behavior have been assessed. Overall, the BCT-type zeolite clearly stands out for highly selective separations of both D2 and T2 over H2, achieving the highest reported selectivities at cryogenic temperatures. We also identified other interesting zeolites for the separation of hydrogen isotopes that offer an alternative way to tackle similar isotopic separations by an aimed selection or design of porous materials.
  • Publication
    Influence of Flexibility on the Separation of Chiral Isomers in the STW-Type Zeolite
    (Wiley, 2018) Bueno-Perez, Rocio; Balestra, Salvador RG; Camblor, Miguel A; Min, Jun Gi; Hong, Suk Bong; Merkling, Patrick; Calero, Sofía
    Molecular simulation, through the computation of adsorption isotherms, is a useful predictive tool for the selective capacity of nanoporous materials. Generally, adsorbents are modelled as rigid frameworks, as opposed to allowing for vibrations of the lattice, and this approximation is assumed to have negligible impact on adsorption. In this work, we test this approach in an especially challenging system by computing the adsorption of the chiral molecules 2-pentanol, 2-methylbutanol and 3-methyl-2-butanol in the all-silica and germanosilicate chiral zeolites STW, and study their lattice vibrations upon adsorption. The analysis of single and multicomponent adsorption isotherms shows the suitability of the STW-type zeolites as molecular sieves for chiral separation processes, which pose a challenging task in the chemical and pharmaceutical industries. We also provide new experimental adsorption data that validate the force field employed. Our results reveal that the lattice vibrations of the all-silica framework are sorbate-independent while those of germanosilicate STW on the other hand display host-guest coupling modulated by uptake and sorbate type that disrupt the chiral recognition sites. This study points out that the effects of intrinsic flexibility on the selective capacity of nanoporous materials may range from low to high impact, some of which could not have been foreseen even after the examination of the structural dynamics of an empty framework.
  • Publication
    Impact of Small Adsorbates in the Vibrational Spectra of Mg- and Zn-MOF-74 Revealed by First-Principles Calculations
    (American Chemical Society, 2020) Romero-Muñiz, Carlos; Gavira-Vallejo, José María; Merkling, Patrick; Calero, Sofía
    In this work, we analyze the influence of small adsorbates on the vibrational spectra of Mg- and Zn-metal−organic framework MOF-74 by means of first-principles calculations. In particular, we consider the adsorption of four representative species of different interaction strengths: Ar, CO2, H2O, and NH3. Apart from a comprehensive characterization of the structural and energetic aspects of empty and loaded MOFs, we use a fully quantum ab initio approach to evaluate the Raman and IR activities of the normal modes, leading to the construction of the whole vibrational spectra. Under this approach, not only are we able to proceed with the complete assignment of the spectra in terms of the usual internal coordinates but also we can discern the most relevant vibrational fingerprints of the adsorbates and their impact on the whole MOF spectra. On the one hand, some of the typical vibrational modes of the small molecules are slightly shifted but still visible when adsorbed on the MOFs, especially those appearing at high wavenumbers where the empty MOFs lack IR/Raman signals. On the other hand, some bands arising from the organic ligands are affected by the presence of the absorbates, displaying non-negligible frequency shifts, in agreement with recent experiments. We find a strong correlation between all of these frequency shifts and the interaction strength of the adsorbate with the hosting framework. The findings presented in this work expand the capabilities of vibrational spectroscopy techniques to analyze porous materials and can be useful for the design of sensors and new devices based on MOF technology.
  • Publication
    Diffusion Patterns in Zeolite MFI: The Cation Effect
    (American Chemical Society, 2018) Pérez Carbajo, Julio; Dubbeldam, David; Calero, Sofía; Merkling, Patrick
    Zeolite MFI is one of the most important stable porous materials used in catalysis and separation processes. However, some fundamental properties remain in the dark, such as the effect of different aluminum distributions on diffusion. This work, through calculations on cation probability densities, guest energy profiles, and diffusion coefficients, provides a consistent picture of accessibility and mobility for two representative adsorbates, methane and carbon dioxide, and helps to explain the stark differences in diffusion behavior among varying aluminum distributions. A distribution was identified close to the practical limit of maximum aluminum substitution and sodium cation content that actually leads to a collapse in diffusion. For all aluminum distributions studied, the diffusion properties are closely linked to the number of cations. Compensating aluminum negative charge with divalent calcium instead of monovalent sodium increases methane but decreases carbon dioxide diffusion. With respect to increasing adsorbate loading, it induces a monotonous decrease in self-diffusivities for all structures studied. This study highlights the desirability of controlling the aluminum substitution location and, more importantly, the fact that two heavily substituted MFI zeolites with identical composition reported in the literature may have very different diffusion properties.
  • 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
    Identifying Zeolite Topologies for Storage and Release of Hydrogen
    (American Chemical Society, 2018-05-18) Martin Calvo, Ana; Gutiérrez Sevillano, Juan José; Matito Martos, Ismael; Vlugt, Thijs J. H.; Calero, Sofía
    We present a molecular simulation study on the most suitable zeolite topologies for hydrogen adsorption and storage. We combine saturation capacities, pore size distributions, preferential adsorption sites and curves of heat of adsorption of hydrogen as function of temperature (we call them HoA-curve) to identify the optimal zeolites for storage and release of hydrogen. Then we analyze the relation between the shape of the HoA-curve and the topology of the materials. We also evaluate the influence of incorporating Feynman-Hibbs effect on the adsorption behavior. We can stablish different shapes on the HoA-curve depending on the uniformity or not of the pores of the zeolites. Parabola-like curves are observed in structures with one or similarly sized pores, while deviations from the parabola are found at low temperature for structures combining large and small pores. The Feynman-Hibbs quantum correction reduces the adsorption capacity of the materials affecting not only the saturation capacity but also the shape of the isotherms. From our results the zeolites studied in this work can be considered potential candidates for the storage and release of hydrogen.
  • Publication
    Separation of benzene from mixtures with water, methanol, ethanol, and acetone: highlighting hydrogen bonding and molecular clustering influences in CuBTC
    (Royal Society of Chemistry, 2015-07-07) Gutiérrez Sevillano, Juan José; Calero, Sofía; Krishna, Rajamani
    Configurational-Bias Monte Carlo (CBMC) simulations are used to establish the potential of CuBTC for separation of water/benzene, methanol/benzene, ethanol/benzene, and acetone/benzene mixtures. For operations under pore saturation conditions, the separations are in favor of molecules that partner benzene; this is due to molecular packing effects that disfavor benzene. CBMC simulations for adsorption of quaternary water/methanol/ethanol/benzene mixtures show that water can be selectively adsorbed at pore saturation, making CuBTC effective in drying applications. Ideal Adsorbed Solution Theory (IAST) calculations anticipate the right hierarchy of component loadings but the quantitative agreement with CBMC mixture simulations is poor for all investigated mixtures. The failure of the IAST to provide reasonable quantitative predictions of mixture adsorption is attributable to molecular clustering effects that are induced by hydrogen bonding between water-water, methanol-methanol, and ethanol-ethanol molecule pairs. There is, however, no detectable hydrogen bonding between benzene and partner molecules in the investigated mixtures. As a consequence of molecular clustering, the activity coefficients of benzene in the mixtures is lowered below unity by one to three orders of magnitude at pore saturation; such drastic reductions cannot be adequately captured by the Wilson model, that does not explicitly account for molecular clustering. Molecular clustering effects are also shown to influence the loading dependence of the diffusivities of guest molecules.
  • Publication
    Selective Adsorption of Water from Mixtures with 1-Alcohols by Exploitation of Molecular Packing Effects in CuBTC
    (American Chemical Society, 2015-01-30) Gutiérrez Sevillano, Juan José; Calero, Sofía; Krishna, Rajamani
    The selective removal of water from mixtures with methanol, ethanol, and 1-propanol is an important task in the processing industries. With the aid of configurational-bias Monte Carlo simulations of unary and mixture adsorption, we establish the potential of CuBTC for this separation task. For operations close to pore saturation conditions, the adsorption is selective to water that has a significantly higher saturation capacity compared to that of 1-alcohols. The water-selective separation relies on subtle entropy effects that manifest near pore saturation conditions. A further distinguishing feature is that mixture adsorption is determined to be strongly nonideal, and the activity coefficients of the constituent components deviate strongly from unity as pore saturation is approached. The predictions of the ideal adsorbed solution theory (IAST), though qualitatively correct, do not predict the component loadings for mixture adsorption with adequate accuracy. Consequently, the activity coefficients, after appropriate parametrization, have been incorporated into the real adsorbed solution theory (RAST). Transient breakthrough simulations, using the RAST model as a basis, demonstrate the capability of CuBTC for selective adsorption of water in fixed-bed adsorption devices operating under ambient conditions.
  • 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
    Solubility of the Precombustion Gases CO2, CH4, CO, H2, N2, and H2S in the Ionic Liquid [bmim][Tf2N] from Monte Carlo Simulations
    (American Chemical Society, 2014-09-22) Ramdin, Mahinder; Balaji, Sayee P.; Vicent Luna, José Manuel; Gutiérrez Sevillano, Juan José; Calero, Sofía; de Loos, Theo W.; Vlugt, Thijs, J. H.
    Monte Carlo simulations were used to compute the solubility of the pure gases CO2, CH4, CO, H2, N2, and H2S in the ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [bmim][Tf2N]. Simulations in the osmotic ensemble were performed to compute absorption isotherms at a temperature of 333.15 K using the versatile continuous fractional component Monte Carlo (CFCMC) method. The predicted gas solubilities and Henry constants are in good agreement with the experimental data. The Monte Carlo simulations correctly predict the observed solubility trend, which obeys the following order: H2S > CO2 > CH4 > CO > N2 > H2. Relevant separation selectivities for the precombustion process are calculated from the pure gas Henry constants and a comparisonwith experimental data is provided