@article {637, title = {Adsorption in heterogeneous porous media: Hierarchical and composite solids}, journal = {Microporous and Mesoporous Materials}, volume = {229}, year = {2016}, month = {Jul-15-2016}, pages = {145 - 154}, abstract = {

Experiment and molecular simulation are used to investigate adsorption in heterogeneous porous media consisting of hierarchical solids (combining different porosity scales) or composite solids (such as silver nanoparticles adsorbed at the external surface of zeolite). It is shown that adsorption in such heterogeneous materials can be written as a linear combination of the adsorption isotherms in its different domains (i.e. porosity scales for the hierarchical sample and constituents for the composite sample). In the case of the composite material, we also show that the linear combination can be used with weighing parameters obtained for a different adsorbate. Such a superimposition principle, which is validated using well-characterized experimental samples, is of interest for characterization purpose as well as industrial applications as they can be used to determine accurately the amount of phases in a given sample (volume corresponding to a given porosity scale or constituent). In contrast, significant departure between the experimental adsorption isotherm and the linear combination can be used to detect coupling effects between the different domains or restrained access to a given domain type. Such a characterization strategy of complex heterogeneous media is complementary to other experiments, such as those probing capillary hysteresis shapes, scanning curves and subloops, which allow determining the distribution of domains within the framework of the independent domain theory. (C) 2016 Elsevier Inc. All rights reserved.

}, issn = {13871811}, doi = {10.1016/j.micromeso.2016.04.011}, url = {https://linkinghub.elsevier.com/retrieve/pii/S1387181116301032}, author = {Deliere, Ludovic and Fran{\c c}ois Villemot and David Farrusseng and Anne Galarneau and Topin, Sylvain and Benoit A. Coasne} } @article {108, title = {Adsorption and Dynamics in Hierarchical Metal-Organic Frameworks}, journal = {Journal of Physical Chemistry C}, volume = {118}, year = {2014}, month = {Apr-10-2014}, pages = {7423-7433}, type = {Article}, abstract = {

Adsorption and dynamics in hierarchical metal-organic frameworks are investigated by means of molecular simulation. The models of hierarchical porous solids are obtained by carving mesopores of different diameters out of a crystal of Cu-BTC (model A) or by inserting a microporous particle of Cu-BTC in an amorphous silica mesopore (model B). We show that the nitrogen adsorption isotherms at 77 K for the solids corresponding to model A can be described as a linear combination of reference adsorption isotherms for pure microporous and mesoporous solids. In contrast, the adsorption isotherms for model B cannot be described accurately as a sum of reference microporous and mesoporous adsorption isotherms. The inserted particle acts as a constriction which helps nucleate the liquid phase within the mesopore so that no capillary condensation hysteresis is observed. The dynamics of nitrogen adsorbed at 77 K inside the porosity of the hierarchical solids is also investigated. The Fickian regime is reached at long times which are not attainable with molecular dynamics simulations. At higher temperature, the faster self-diffusion makes it possible to obtain the diffusivity of the adsorbate. Nitrogen adsorbed in the microporosity of the hierarchical porous solids has a self-diffusion coefficient close to that of nitrogen adsorbed in pure Cu-BTC. In contrast, diffusion in the mesoporosity is faster than in the microporosity so that the overall diffusivity is faster than in pure Cu-BTC.

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}, issn = {1932-7447}, doi = {10.1021/jp500037z}, author = {Fran{\c c}ois Villemot and Anne Galarneau and Benoit A. Coasne} } @article {64, title = {Adsorption-based characterization of hierarchical metal{\textendash}organic frameworks}, journal = {Adsorption}, volume = {20}, year = {2014}, month = {Feb-2014}, pages = {349-357}, abstract = {

Nitrogen adsorption at 77 K on metal\–organic framework (MOF) is investigated by means of molecular simulations. We consider both regular Cu\–BTC crystal and a MOF-based hierarchical porous solid consisting of a mesopore carved out of a Cu\–BTC crystal. The t-plot method is applied to these solids by using a non-porous Cu\–BTC surface as the reference sample. The values of the mesoporous and external surface areas are determined from the t-plot, and the validity of the method for this type of hierarchical solid is discussed.

}, keywords = {Adsorption, Hierarchical porous materials, Molecular simulation, t-Plot}, issn = {0929-5607}, doi = {10.1007/s10450-013-9583-7}, author = {Fran{\c c}ois Villemot and Anne Galarneau and Benoit A. Coasne} } @article {83, title = {Ionic liquid confined in silica nanopores: molecular dynamics in the isobaric-isothermal ensemble}, journal = {Molecular Physics}, volume = {112}, year = {2014}, month = {Avr-03-2014}, pages = {1350-1361}, type = {Article}, abstract = {

Molecular dynamics simulations in the isobaric-isothermal ensemble are used to investigate the structure and dynamics of an ionic liquid confined at ambient temperature and pressure in hydroxylated amorphous silica nanopores. The use of the isobaric-isothermal ensemble allows estimating the effect of confinement and surface chemistry on the density of the confined ionic liquid. The structure of the confined ionic liquid is investigated using density profiles and structural order parameters while its dynamics is assessed by determining the mobility and ionic conductivity of the confined phase. Despite the important screening of the electrostatic interactions (owing to the small Debye length in ionic liquids), the local structure of the confined ionic liquid is found to be mostly driven by electrostatic interactions. We show that both the structure and dynamics of the confined ionic liquid can be described as the sum of a surface contribution arising from the ions in contact with the surface and a bulk-like contribution arising from the ions located in the pore centre; as a result, most properties of the confined ionic liquid are a simple function of the surface-to-volume ratio of the host porous material. In contrast, the ionic conductivity of the confined ionic liquid, which is a collective dynamical property, is found to be similar to the bulk. This study sheds light on the complex behaviour of hybrid materials made up of ionic liquid confined in inorganic porous materials.

}, keywords = {amorphous silica, ionic liquids, molecular dynamics, surface}, issn = {0026-8976}, doi = {10.1080/00268976.2014.902138}, author = {Guido Ori and Fran{\c c}ois Villemot and Lydie Viau and Andre Vioux and Benoit A. Coasne} } @article {92, title = {Validity of the t-plot Method to Assess Microporosity in Hierarchical Micro/Mesoporous Materials}, journal = {Langmuir}, volume = {30}, year = {2014}, month = {Nov-2014}, pages = {13266-13274}, type = {Article}, abstract = {
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The t-plot method is a well-known technique which allows determining the micro- and/or mesoporous volumes and the specific surface area of a sample by comparison with a reference adsorption isotherm of a nonporous material having the same surface chemistry. In this paper, the validity of the t-plot method is discussed in the case of hierarchical porous materials exhibiting both micro- and mesoporosities. Different hierarchical zeolites with MCM-41 type ordered mesoporosity are prepared using pseudomorphic transformation. For comparison, we also consider simple mechanical mixtures of microporous and mesoporous materials. We first show an intrinsic failure of the t-plot method; this method does not describe the fact that, for a given surface chemistry and pressure, the thickness of the film adsorbed in micropores or small mesopores (\< 10\σ, \σ being the diameter of the adsorbate) increases with decreasing the pore size (curvature effect). We further show that such an effect, which arises from the fact that the surface area and, hence, the free energy of the curved gas/liquid interface decreases with increasing the film thickness, is captured using the simple thermodynamical model by Derjaguin. The effect of such a drawback on the ability of the t-plot method to estimate the micro- and mesoporous volumes of hierarchical samples is then discussed, and an abacus is given to correct the underestimated microporous volume by the t-plot method.

}, issn = {0743-7463}, doi = {10.1021/la5026679}, author = {Anne Galarneau and Fran{\c c}ois Villemot and Rodriguez, Jeremy and Fajula, Fran{\c c}ois and Benoit A. Coasne} } @article {81, title = {Adsorption-based characterization of hierarchical metal-organic frameworks}, journal = {Adsorptio-Journal of the International Adsorption Society}, volume = {20}, year = {2013}, month = {Oct-06-2013}, pages = {349-357}, type = {Article}, abstract = {

Nitrogen adsorption at 77 K on metal-organic framework (MOF) is investigated by means of molecular simulations. We consider both regular Cu-BTC crystal and a MOF-based hierarchical porous solid consisting of a mesopore carved out of a Cu-BTC crystal. The t-plot method is applied to these solids by using a non-porous Cu-BTC surface as the reference sample. The values of the mesoporous and external surface areas are determined from the t-plot, and the validity of the method for this type of hierarchical solid is discussed.

}, keywords = {Adsorption, Hierarchical porous materials, Molecular simulation, t-Plot}, issn = {0929-5607}, doi = {10.1007/s10450-013-9583-7}, author = {Fran{\c c}ois Villemot and Anne Galarneau and Benoit A. Coasne} } @article {34, title = {Molecular simulation of adsorption and transport in hierarchical porous materials}, journal = {Langmuir}, volume = {29}, year = {2013}, month = {May-29-2013}, pages = {7864{\textendash}7875}, abstract = {

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Adsorption and transport in hierarchical porous solids with micro- (\∼1 nm) and mesoporosities (\>2 nm) are investigated by molecular simulation. Two models of hierarchical solids are considered: microporous materials in which mesopores are carved out (model A) and mesoporous materials in which microporous nanoparticles are inserted (model B). Adsorption isotherms for model A can be described as a linear combination of the adsorption isotherms for pure mesoporous and microporous solids. In contrast, adsorption in model B departs from adsorption in pure microporous and mesoporous solids; the inserted microporous particles act as defects, which help nucleate the liquid phase within the mesopore and shift capillary condensation toward lower pressures. As far as transport under a pressure gradient is concerned, the flux in hierarchical materials consisting of microporous solids in which mesopores are carved out obeys the Navier\–Stokes equation so that Darcy\’s law is verified within the mesopore. Moreover, the flow in such materials is larger than in a single mesopore, due to the transfer between micropores and mesopores. This nonzero velocity at the mesopore surface implies that transport in such hierarchical materials involves slippage at the mesopore surface, although the adsorbate has a strong affinity for the surface. In contrast to model A, flux in model B is smaller than in a single mesopore, as the nanoparticles act as constrictions that hinder transport. By a subtle effect arising from fast transport in the mesopores, the presence of mesopores increases the number of molecules in the microporosity in hierarchical materials and, hence, decreases the flow in the micropores (due to mass conservation). As a result, we do not observe faster diffusion in the micropores of hierarchical materials upon flow but slower diffusion, which increases the contact time between the adsorbate and the surface of the microporosity.

}, doi = {10.1021/la401228k}, author = {Benoit A. Coasne and Anne Galarneau and Gerardin, Corine and Fajula, Fran{\c c}ois and Fran{\c c}ois Villemot} }