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  • Publication
    Revisión del desastre del camping de Biescas desde la perspectiva de la gestión de Reducción de Riesgos de Desastres (RRD) y sus consecuencias jurídicas.
    (Sociedad Geológica de España, 2012) Zango-Pascual, Marga
    La inundación del camping de Biescas ocurrida en 1996 en el Pirineo Oscense, causó 87 víctimas mortales e importantes daños y víctimas indirectas. Se han analizado desde entonces muchos aspectos relativos a las geociencias aunque no es tan conocido el desenlace jurídico del caso, que dio lugar a varias sentencias y pasó por las jurisdicciones civil, penal y contencioso-administrativa. En 2005 la Audiencia Nacional emitió sentencia condenatoria contra varias administraciones públicas españolas. Suele desconocerse que este caso es considerado en España como el primero en el hubo una intervención psicológica en un desastre y sirvió para el desarrollo y evolución de la psicología de catástrofes. La sentencia incide y permite reflexionar sobre dos conceptos esenciales, “fuerza mayor” y “la responsabilidad por acción-omisión de las administraciones públicas”. En bastantes ocasiones resultan fundamentales en la forma en que se gestiona o no un determinado riesgo y por tanto en la posibilidad de que acabe convirtiéndose en un desastre. La aplicabilidad de las geociencias en la sociedad implicaría conocer y valorar estos aspectos infra-conocidos y enlazarlos con los enfoques actuales de la Estrategia Internacional de Reducción de Riesgos de Desastres de Naciones Unidas, y la Gestión de Reducción de Riesgos en general.
  • Publication
    Metodología para la detección de riesgos geológico-geotécnicos en las fases iniciales de las infraestructuras lineales. Implementación para un sistema GIS
    (Sociedad Geológica de España, 2004) Zango-Pascual, Marga
    A great part of budget rises in the building and operating of transportation routes at surface in Civil Engeneering (highways, railways, canals,...) are frequently caused by geological or geological-geotechical factors, including those risks arisen once the works have begun. In this work a methodology for the initial phases of design and conception of linear civil engeneering works is proposed. This methodology consists in the analysis of 12 geological-geotechical aspects or variables (e.g. slope stability, rock mass discontinuities, expansivity, erodability, ripping), each of one is evaluated and clasified in four classes, from 0 to 3 (from favourable to unfavourable). This evaluation process requires a certain degree of experience. In a second step the variables are weighed according to their relative importance and they are implemented using a GIS in order to obtain a characterization of the territory in five degrees according to the risk valoration o f its behaviour in civil engeneering works. In the initial phases o f design this new methodology, o f very low cost but of very high performance, could be very useful because singular aspects of the land behaviour during the construction and operation time should be detected. So, it could anticipate some problems in the construction and operation of the work, usually observed once the work is initiated, whose resolution generally implies in these phases important costs.
  • Publication
    Instrumentos Jurídicos Internacionales para la Reducción de Desastres Naturales. Del DIRDN al Marco de Hyogo y la reivindicación del papel de la geología en la Reducción de Riesgo de Desastres (RDD)
    (Sociedad Geológica de España, 2012) Zango-Pascual, Marga
    Se considera a nivel global que la Década del DIRDN (1990-99) ha sido significativa en avances científicos, pero no así en su aplicación y difusión a efectos prácticos. El análisis realizado a mitad de período por el Secretariado General de Naciones Unidas sobre los logros del Marco de Acción de Hyogo (MAH 2005-2015) destaca que aunque ha servido para orientar las actividades mundiales encaminadas a reducir el riesgo de desastres, no se ha avanzado igual en la reducción del riesgo de desastres, pues aún no está sólidamente integrada en los procesos operativos de los sectores de desarrollo, los ministerios de planificación y las instituciones financieras. Es importante recordar que los desastres pueden producirse tanto como consecuencia de la acción humana como de la inacción, y respecto a amenazas naturales, es frecuente la inacción, entendida como: aplicación o no de códigos constructivos, trasmisión y aplicación de los avances científicos, elaboración de estrategias y políticas públicas específicas en zonas con alto o medio riesgo, e incluso, la no inclusión de la preparación para estos riesgos en las políticas públicas. Se incide en el papel de la geología y las geociencias en la consecución de los objetivos del MAH.
  • Publication
    Reconstructing the Western North Pacific Summer Monsoon since the Late Nineteenth Century
    (American Meteorological Society, 2018-01-01) Vega Inmaculada; Gallego Puyol David; Ribera Rodríguez Pedro; Gómez Delgado Francisco de Paula; García Herrera Ricardo; Peña Ortiz, Cristina
    A new index, the western North Pacific directional index (WNPDI), based on historical wind direction observations taken aboard sailing ships, has been developed to characterize the western North Pacific summer monsoon (WNPSM) since 1898. The WNPDI measures the persistence of the surface westerly winds in the region 58–158N, 1008–1308E and easterly winds in the region 208–308N, 1108–1408E, exhibiting a consistent relationship with the summer precipitation in the areas affected by the WNPSM throughout the entire twentieth century. Its length doubles that of the previous WNPSM index (1948–2014) based on reanalysis products, which allows uncovering different relevant features of the WNPSM variability. The WNPSM had a significant interdecadal variability throughout the twentieth century. In particular, the period 1918–48 was characterized by less variable and stronger monsoons than in recent decades. Additionally, the relationship between the WNPSM and ENSO or El Niño Modoki has been evaluated during the entire twentieth century for the first time. It is confirmed that the WNPSM tends to be strong (weak) when El Niño (La Niña) develops during the whole record. Nevertheless, the relationship during the ENSO-decaying phase is not stable in time. Thus, the WNPSM tended to be strong (weak) when La Niña (El Niño) decayed only since the late 1950s, with an opposite relationship in the earliest part of the record. El Niño Modoki shows a rather stable and high correlation with the WNPDI during the whole study period throughout the twentieth century
  • Publication
    Tropical Deep Convection Impact on Southern Winter Stationary Waves and Its Modulation by the Quasi-Biennial Oscillation
    (American Meteorological Society, 2019-11-01) Peña Ortiz, Cristina; Manzini Elisa; Giorgetta Marco
    The impact of tropical deep convection on southern winter stationary waves and its modulation by the quasi-biennial oscillation (QBO) have been investigated in a long (210 year) climate model simulation and in ERA-Interim reanalysis data for the period 1979–2018. Model results reveal that tropical deep convection over the region of its climatological maximum modulates high-latitude stationary planetary waves in the southern winter hemisphere, corroborating the dominant role of tropical thermal forcing in the generation of these waves. In the tropics, deep convection enhancement leads to wavenumber-1 eddy anomalies that reinforce the climatological Rossby–Kelvin wave couplet. The Rossby wave propagates toward the extratropical southern winter hemisphere and upward through the winter stratosphere reinforcing wavenumber-1 climatological eddies. As a consequence, stronger tropical deep convection is related to greater upward wave propagation and, consequently, to a stronger Brewer–Dobson circulation and a warmer polar winter stratosphere. This linkage between tropical deep convection and the Southern Hemisphere (SH) winter polar vortex is also found in the ERA-Interim reanalysis. Furthermore, model results indicate that the enhancement of deep convection observed during the easterly phase of the QBO (E-QBO) gives rise to a similar modulation of the southern winter extratropical stratosphere, which suggests that the QBO modulation of convection plays a fundamental role in the transmission of the QBO signature to the southern stratosphere during the austral winter, revealing a new pathway for the QBO–SH polar vortex connection. ERA-Interim corroborates a QBO modulation of deep convection; however, the shorter data record does not allow us to assess its possible impact on the SH polar vortex.
  • Publication
    Evidence of rapid adaptation integrated into projections of temperature-related excess mortality
    (IOPscience, 2022-04-08) Huber Veronika; Peña Ortiz, Cristina; Gallego Puyol David; Lange Stefan; Sera Francesco
    Few studies have used empirical evidence of past adaptation to project temperature-related excess mortality under climate change. Here, we assess adaptation in future projections of temperature-related excess mortality by employing evidence of shifting minimum mortality temperatures (MMTs) concurrent with climate warming of recent decades. The study is based on daily non-external mortality and daily mean temperature time-series from 11 Spanish cities covering four decades (1978–2017). It employs distributed lag non-linear models (DLNMs) to describe temperature-mortality associations, and multivariate mixed-effect meta-regression models to derive city- and subperiod-specific MMTs, and subsequently MMT associations with climatic indicators. We use temperature projections for one low- and one high-emission scenario (ssp126, ssp370) derived from five global climate models. Our results show that MMTs have closely tracked mean summer temperatures (MSTs) over time and space, with meta-regression models suggesting that the MMTs increased by 0.73 °C (95%CI: 0.65, 0.80) per 1 °C rise in MST over time, and by 0.84 °C (95%CI: 0.76, 0.92) per 1 °C rise in MST across cities. Future projections, which include adaptation by shifting MMTs according to observed temporal changes, result in 63.5% (95%CI: 50.0, 81.2) lower heat-related excess mortality, 63.7% (95%CI: 30.2, 166.7) higher cold-related excess mortality, and 11.2% (95%CI: −5.5, 39.5) lower total temperature-related excess mortality in the 2090s for ssp370 compared to estimates that do not account for adaptation. For ssp126, assumptions on adaptation have a comparatively small impact on excess mortality estimates. Elucidating the adaptive capacities of societies can motivate strengthened efforts to implement specific adaptation measures directed at reducing heat stress under climate change.
  • Publication
    Processes influencing lower stratospheric water vapour in monsoon anticyclones: insights from Lagrangian modelling
    (European Geophysical Union, 2021-06-28) Plaza Martín Nuria; Podglajen Aurélien; Peña Ortiz, Cristina; Ploeger Felix
    We investigate the influence of different chemical and physical processes on the water vapour distribution in the lower stratosphere (LS), in particular in the Asian and North American monsoon anticyclones (AMA and NAMA, respectively). Specifically, we use the chemistry transport model CLaMS to analyse the effects of large-scale temperatures, methane oxidation, ice microphysics, and small-scale atmospheric mixing processes in different model experiments. All these processes hydrate the LS and, particularly, the AMA. While ice microphysics has the largest global moistening impact, it is small-scale mixing which dominates the specific signature in the AMA in the model experiments. In particular, the small-scale mixing parameterization strongly contributes to the water vapour transport to this region and improves the simulation of the intra-seasonal variability, resulting in a better agreement with the Aura Microwave Limb Sounder (MLS) observations. Although none of our experiments reproduces the spatial pattern of the NAMA as seen in MLS observations, they all exhibit a realistic annual cycle and intra-seasonal variability, which are mainly controlled by large-scale temperatures. We further analyse the sensitivity of these results to the domain-filling trajectory set-up, herecalled Lagrangian trajectory filling (LTF). Compared with MLS observations and with a multiyear reference simulation using the full-blown chemistry transport model version of CLaMS, we find that the LTF schemes result in a drier global LS and in a weaker water vapour signal over the monsoon regions, which is likely related to the specification of the lower boundary condition. Overall, our results emphasize the importance of subgrid-scale mixing and multiple transport pathways from the troposphere in representing water vapour in the AMA.
  • Publication
    Internal variability and external forcings in the ocean–atmosphere multidecadal oscillator over the North Atlantic
    (Springer Link, 2020-05-23) Ribera Rodríguez Pedro; Ordónez Paulina; Gallego Puyol David; Peña Ortiz, Cristina
    In this paper, we generalize the concept of “external forcing” to include any mechanism that modulates the long-term evolution of a meteorological variable but is not directly related to the internal variability of the climate system. Applying this concept, the corresponding ‘external forcings’ are removed from several long record datasets of oceanic and atmospheric variables at the surface in the North Atlantic. We perform a multivariate analysis in the frequency domain over both the original data felds and the new ‘internal variability’ felds. This multivariate analysis is based on a MultiTaper Method-Singular Value Decomposition (MTM-SVD). It is noteworthy that, after the removal of the external forcings, there is an almost perfect alignment of the main multidecadal oscillatory band (f=0.21 cycles/decade) with all the spectra of the analysed felds. This alignment was not observed before the external forcings were removed. Particularly striking is the case of the sea level pressure (SLP), which shows a notable variation in its oscillation period despite the fact that this variable has traditionally been considered to be unafected, at global scale, by any external forcing. The external forcing in the SLP records is very probably caused by the scarcity of the observed data during the frst hundred years of the record (most evident, during the earliest decades), by the spatial distribution of those observations and, possibly, by the assimilation model employed to build those long record datasets. When we analysed the relationship between the ocean and the atmosphere using this approach, we found strong evidence of a cyclic behaviour in which oceanic conditions modulate the atmospheric variability, with a lead time of up to about 10 years.
  • Publication
    Temperature-related excess mortality in German cities at 2 °C and higher degrees of global warming
    (Elsevier, 2020-03-29) Huber, Veronika; Krummenauerb Linda; Peña Ortiz, Cristina; Lange Stefan; Gasparrini Antonio; Vicedo-Cabrera Ana M.; García Herrera Ricardo; Frielerb Katja
    Background Investigating future changes in temperature-related mortality as a function of global mean temperature (GMT) rise allows for the evaluation of policy-relevant climate change targets. So far, only few studies have taken this approach, and, in particular, no such assessments exist for Germany, the most populated country of Europe. Methods We assess temperature-related mortality in 12 major German cities based on daily time-series of all-cause mortality and daily mean temperatures in the period 1993–2015, using distributed-lag non-linear models in a two-stage design. Resulting risk functions are applied to estimate excess mortality in terms of GMT rise relative to pre-industrial levels, assuming no change in demographics or population vulnerability. Results In the observational period, cold contributes stronger to temperature-related mortality than heat, with overall attributable fractions of 5.49% (95%CI: 3.82–7.19) and 0.81% (95%CI: 0.72–0.89), respectively. Future projections indicate that this pattern could be reversed under progressing global warming, with heat-related mortality starting to exceed cold-related mortality at 3 °C or higher GMT rise. Across cities, projected net increases in total temperature-related mortality were 0.45% (95%CI: −0.02–1.06) at 3 °C, 1.53% (95%CI: 0.96–2.06) at 4 °C, and 2.88% (95%CI: 1.60–4.10) at 5 °C, compared to today's warming level of 1 °C. By contrast, no significant difference was found between projected total temperature-related mortality at 2 °C versus 1 °C of GMT rise. Conclusions Our results can inform current adaptation policies aimed at buffering the health risks from increased heat exposure under climate change. They also allow for the evaluation of global mitigation efforts in terms of local health benefits in some of Germany's most populated cities.
  • Publication
    Long term variability of the northerly winds over the Eastern Mediterranean as seen from historical wind observations
    (ELSEVIER, 2018-10-29) Gómez Delgado, Francisco de Paula; Gallego Puyol, David; Peña Ortiz, Cristina; Vega Martín, Inmaculada; Ribera, Pedro; Gracía Herrera Ricardo
    The summer circulation over the eastern Mediterranean is characterized by a persistent northerly regime whose interannual variability is modulated both by mid and tropical latitudes. In this paper, we use historical wind observations taken aboard ships to assemble the first purely instrumental index quantifying this wind system since 1880. This has allowed evaluating the multidecadal and interannual variability of the northerlies in the eastern Mediterranean over the longest time period so far. Our results indicate that the first half of the 20th century was characterized by more frequent and persistent northerly winds in the eastern Mediterranean than the second half. We have also found that the well-known teleconnection between the eastern Mediterranean summertime winds and the Indian Summer Monsoon, with enhanced northerlies concurrent with a stronger monsoon, has not been steady along the 20th century. It is shown that the Indian summer monsoon modulation of convection over the western Indian Ocean plays a crucial role in the strength of this connection.
  • 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.
  • Publication
    A DFT-based simulated annealing method for the optimization of global energy in zeolite framework systems: Application to natrolite, chabazite and clinoptilolite
    (Elsevier, 2019-12-26) Abatal, M.; Ruiz-Salvador, A. Rabdel; Cruz Hernández, N.
    Modeling zeolites structure including strongly interaction extra-framework species by using DFT is still a difficult task now a day. To face this problem, we have introduced here a simulated annealing (SA) method to obtain global minimum energies. This approximation has been applied to describing the structure of free common zeolites. Basically, the SA idea is to perform a molecular dynamics (MD) by increasing the temperature steps by steps to overcome local energy minima, after that, by subsequent energy optimization it is possible to move to a different local minimum. This procedure was done up to the temperatures of 300 and 400 K. MD, as well as, geometry optimization were carried out in a periodic framework and dispersion corrected Density Functional Theory (DFT) calculations using VASP. The results show that it seems to be very important to accomplish SA calculation in order to obtain an adequate global minimum, reducing the energy of the system up to . The impact on computing interaction energies with adsorbed molecules is high, with large implications in predicting adsorption, separation, ion-exchange and catalytic properties. Our results are in good agreement with known experimental and theoretical literature.
  • Publication
    Risk and vulnerability assessment in coastal environments applied to heritage buildings in Havana (Cuba) and Cadiz (Spain)
    (Elsevier, 2021-01-01) Betzaida Rodríguez-Rosales; Dahimi Abreu; Ortiz Calderón, Rocío; Becerra Luna, Javier; Ana E. Cepero; Ortiz, Pilar; M. A. Vázquez
    In this paper, diagnostic tools are utilized to conduct a vulnerability analysis of monuments located in a coastal environment in accordance with a raft of standards drawn up by the International Organization for Standardization (ISO) 31000, in order to identify the main risks for Cultural Heritage in Havana (Cuba) and Cadiz (Spain). Vulnerability analysis is based on a Leopold matrix, which models the relationship between major hazards and pathologies in order to evaluate coastal influence and the risks for the conservation of cultural heritage. The quantitative matrix allows for a cause-effect analysis to be conducted for the main scenarios, related to the state of conservation. These relationships are a key step in risk assessment and treatment strategies. Major hazards have been identified by different public bodies and agencies to provide information about the probability and intensity of these variables in the vulnerability matrix. The combination of vulnerability index assessment, which depends on intrinsic variables and environmental scenarios, and knowledge of the main hazards in Havana and Cadiz, has provided useful tools to conduct risk assessments for cultural heritage conservation in coastal environments,where climate conditions, geomorphology and social issues are the main hazards, while vulnerability is associated with conservation plans. These tools provide information that will enable decision-makers in different coastal environments to prioritize strategies for cultural heritage preservation.
  • Publication
    Molecular Simulation Investigation into the Performance of Cu-BTC Metal Organic Frameworks for Carbon Dioxide-Methane Separations
    (RSC publishing, 2011-10-13) Gutiérrez Sevillano, Juan José; Caro Pérez, Alejandro; David Dubbeldam; Calero, Sofía
    We report a molecular simulation study for Cu–BTC metal–organic frameworks as carbon dioxide–methane separation devices. For this study we have computed adsorption and diffusion of methane and carbon dioxide in the structure, both as pure components and mixtures over the full range of bulk gas compositions. From the single component isotherms, mixture adsorption is predicted using the ideal adsorbed solution theory. These predictions are in very good agreement with our computed mixture isotherms and with previously reported data. Adsorption and diffusion selectivities and preferential sitings are also discussed with the aim to provide new molecular level information for all studied systems.
  • Publication
    Understanding Nanopore Window Distortions in the Reversible Molecular Valve Zeolite RHO
    (American Chemical Society, 2015-07-14) S. R. G. Balestra, S. Hamad, A. R. Ruiz-Salvador, V. Domínguez−García, P. J. Merkling, D. Dubbeldam, and S. Calero; Ruiz-Salvador, A. Rabdel; Merkling, Patrick; Calero, Sofía
    Molecular valves are becoming popular for potential biomedical applications. However, little is known concerning their performance in energy and environmental areas. Zeolite RHO shows unique pore deformations upon changes in hydration, cation siting, cation type, or temperature–pressure conditions. By varying the level of distortion of double eight-rings, it is possible to control the adsorption properties, which confer a molecular valve behavior to this material. We have employed interatomic potentials-based simulations to obtain a detailed atomistic view of the structural distortion mechanisms of zeolite RHO, in contrast with the averaged and space group restricted information provided by diffraction studies. We have modeled four aluminosilicate structures, containing Li+, Na+, K+, Ca2+ cations. The distortions of the three different zeolite rings are coupled, and the six- and eight-membered rings are largely flexible. A large dependence on the polarizing power of the extra-framework cations and with the loading of water has been found for the minimum aperture of the eight-membered rings that control the nanovalve effect. The calculated energy barriers for moving the cations across the eight-membered rings are very high, which explains the experimentally observed slow kinetics of the phase transition as well as the appearance of metastable phases.
  • Publication
    Controlling Thermal Expansion: A Metal–Organic Frameworks Route
    (American Chemical Society, 2016-10-25) Salvador R. G. Balestra, Rocio Bueno-Perez, Said Hamad, David Dubbeldam, A. Rabdel Ruiz-Salvador, and Sofia Calero; Ruiz-Salvador, A. Rabdel; Calero, Sofía
    Controlling thermal expansion is an important, not yet resolved, and challenging problem in materials research. A conceptual design is introduced here, for the first time, for the use of metal–organic frameworks (MOFs) as platforms for controlling thermal expansion devices that can operate in the negative, zero, and positive expansion regimes. A detailed computer simulation study, based on molecular dynamics, is presented to support the targeted application. MOF-5 has been selected as model material, along with three molecules of similar size and known differences in terms of the nature of host–guest interactions. It has been shown that adsorbate molecules can control, in a colligative way, the thermal expansion of the solid, so that changing the adsorbate molecules induces the solid to display positive, zero, or negative thermal expansion. We analyze in depth the distortion mechanisms, beyond the ligand metal junction, to cover the ligand distortions, and the energetic and entropic effect on the thermo-structural behavior. We provide an unprecedented atomistic insight on the effect of adsorbates on the thermal expansion of MOFs as a basic tool toward controlling the thermal expansion.
  • Publication
    Understanding the stability and structural properties of Ordered Nanoporous Metals towards their rational synthesis
    (Royal Society (UK), 2022-10-05) J. M. Ortiz-Roldan, S. R. G. Balestra, R. Bueno-Perez, S. Calero, E. Garcia-Perez, C. R. A. Catlow, A. R. Ruiz-Salvador, S. Hamad; Calero, Sofía; Ruiz-Salvador, A. Rabdel
    Ordered Nanoporous Metals (ONMs) form a new family of nanoporous materials composed only of pure metals. The expected impact is considerable from combining the ordered nanopore structure of MOFs, zeolites and carbon schwartzites with the robustness and electronic conductivity of metals. Little is known about their stability and structural features. Here we address these points to provide clues toward their rational synthesis, introducing an automatic atomistic design that uses model building and molecular dynamics structural relaxation, and is validated against the experimentally known ONMs. Analysing the properties of the 10 stable structures out of the 17 studied (14 of which are designed in this work) using four noble metals (Pt, Pd, Au and Ag), we have deciphered some key elements and structural descriptors that provide guidelines for the experimental synthesis of ONMS. The long-lived metastability of the stable ONMs is evidenced by the high free energy landscape, computed via Metadynamic simulations. The new ONMs permit molecular diffusion of various molecules of industrial relevance, increasing the expectation for their use in catalysis, separation, nanofiltration, batteries, fuel cells, etc. Stable low-cost ONMs are predicted using Earth-abundant Ni metal, which maintains the main features of their relative noble metal forms.
  • Publication
    Nucleation of Zeolitic Imidazolate Frameworks: from molecules to nanoparticles
    (Royal Society of Chemistry (UK), 2023-01-04) S. R. G. Balestra, B. Martínez-Haya, N. C. Hernández, D. W. Lewis, S. M. Woodley, R. Semino, G. Maurin, A. R. Ruiz-Salvador and S. Hamad,; Ruiz-Salvador, A. Rabdel
    We have studied the clusters involved in the initial stages of nucleation of Zeolitic Imidazolate Frameworks, employing a wide range of computational techniques. In the pre-nucleating solution, the prevalent cluster is the ZnIm4 cluster (formed by a zinc cation, Zn2+, and four imidazolate anions, Im−), although clusters such as ZnIm3, Zn2Im7, Zn2Im7, Zn3Im9, Zn3Im10, or Zn4Im12 have energies that are not much higher, so they would also be present in solution at appreciable quantities. All these species, except ZnIm3, have a tetrahedrally coordinated Zn2+ cation. Small ZnxImy clusters are less stable than the ZnIm4 cluster. The first cluster that is found to be more stable than ZnIm4 is the Zn41Im88 cluster, which is a disordered cluster with glassy structure. Bulk-like clusters do not begin to be more stable than glassy clusters until much larger sizes, since the larger cluster we have studied (Zn144Im288) is still less stable than the glassy Zn41Im88 cluster, suggesting that Ostwald's rule (the less stable polymorph crystallizes first) could be fulfilled, not for kinetic, but for thermodynamic reasons. Our results suggest that the first clusters formed in the nucleation process would be glassy clusters, which then undergo transformation to any of the various crystal structures possible, depending on the kinetic routes provided by the synthesis conditions. Our study helps elucidate the way in which the various species present in solution interact, leading to nucleation and crystal growth.
  • Publication
    Analysis of the ITQ-12 Zeolite Performance in Propane−Propylene Separations Using a Combination of Experiments and Molecular Simulations
    (ACS Publications, 2010-08-13) Gutiérrez Sevillano, Juan José; Dubbeldam, David; Rey, Fernando; Valencia, Susana; Palomino, Miguel; Martin Calvo, Ana; Calero, Sofía
    We present a combined computational and experimental approach to evaluate the suitability of the ITQ-12 nanoporous material (ITW) as a propane-propylene separation device. For this, we have computed adsorption and diffusion of propane and propylene in the ITQ-12 zeolite. The propane isotherm is reproduced well, but the available propylene models in the literature are unable to describe the propylene isotherm. Newly developed force field parameters for propylene were obtained by fitting to our own experimental adsorption isotherms and validated with previous data taken from the literature. To obtain self-diffusion of propane and propylene in the zeolite, we combined the configurational-bias Monte Carlo method with rare-event molecular simulation techniques. Our results support experimental observations that point out ITQ-12 as a suitable structure for propane-propylene separation. The selectivity originates mainly from a difference in adsorption, possibly enhanced by a difference in diffusion.
  • Publication
    Understanding Gas-Induced Structural Deformation of ZIF-8
    (American Chemical Society, 2012-04) Ania, Conchi O.; García Pérez, Elena; Haro, M.; Gutiérrez Sevillano, Juan José; Valdés-Solís, T.; Parra, J.B.; Calero, Sofía
    ZIF-8 is a zeolitic imidazolate framework with very good thermal and chemical stability that opens up many applications that are not feasible by other metal−organic frameowrks (MOFs) and zeolites. Several works report the adsorption properties of ZIF-8 for strategic gases. However, despite the vast experimental corpus of data reported, there seems yet to be a dearth in the understanding of the gas adsorption properties. In this work we provide insights at a molecular level on the mechanisms governing the ZIF-8 structural deformation during molecular adsorption. We demonstrate that the ZIF-8 structural deformation during the adsorption of different molecules at cryogenic temperature goes beyond the gas-induced rotation of the imidazolate linkers. We combine experimental and simulation studies to demonstrate that this deformation is governed by the polarizability and molecular size and shape of the gases, and that the stepped adsorption behavior is defined by the packing arrangement of the guest inside the host.