Toward an Understanding of the Microstructure and Interfacial Properties of PIMs/ZIF-8 Mixed Matrix Membranes

A study integrating advanced experimental and modeling tools was undertaken to characterize the microstructural and interfacial properties of mixed matrix membranes (MMMs) composed of the zeolitic imidazolate framework ZIF-8 nanoparticles (NPs) and two polymers of intrinsic microporosity (PIM-1 and PIM-EA-TB). Analysis probed both the initial ZIF-8/PIM-1 colloidal suspensions and the final hybrid membranes. By combination of dynamic light scattering (DLS) and transmission electron microscopy (TEM) analytical and imaging techniques with small-angle X-ray scattering (SAXS), the colloidal suspensions were shown to consist mainly of two distinct kinds of particles, namely, polymer aggregates of about 200 nm in diameter and densely packed ZIF-8-NP aggregates of a few 100 nm in diameter with a 3 nm thick polymer top-layer. Such aggregates are likely to impart the granular texture of ZIF-8/PIMs MMMs as shown by SEM-XEDS analysis. At the molecular scale, modeling studies showed that the surface coverage of ZIF-8 NPs by both polymers appears not to be optimal with the presence of microvoids at the interfaces that indicates only a moderate compatibility between the polymer and ZIF-8. This study shows that the microstructure of MMMs results from a complex interplay between the ZIF-8/PIM compatibility, solvent, surface chemistry of the ZIF-8 NPs, and the physicochemical properties of the polymers such as molecular structure and rigidity

Computer modelling of halocarbon sorption in zeolite Y

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Cation mobility and the sorption of chloroform in zeolite NaY

International audienceMolecular dynamics simulations at temperatures of 270, 330, and 390 K have been carried out to address the question of cation migration upon chloroform sorption in sodium zeolite Y. The results show that sodium cations located in different sites exhibit different types of mobility. These may be summarized as follows: (1) SII cations migrate toward the center of the supercage upon sorption, due to interactions with the polar sorbate molecules. (2) SI‘ cations hop from the sodalite cage into the supercage to fill vacant SII sites. (3) SI‘ cations migrate to other SI‘ sites within the same sodalite cage. (4) SI cations hop out of the double six-rings into SI‘ sites. In some instances, concerted motion of cations is observed. Furthermore, former SI‘ and SI cations, having crossed to SII sites, may then further migrate within the supercage, as in (1). The cation motion is dependent on the level of sorbate loading, with 10 molecules per unit cell not being enough to induce significant cation displacements, whereas the sorption of 40 molecules per unit cell results in a number of cations being displaced from their original positions. Further rearrangement of the cation positions is observed upon evacuation of the simulation cell, with some cations reverting back to sites normally occupied in bare NaY

Microscopic Model of the Metal-Organic Framework/Polymer Interface: A First Step toward Understanding the Compatibility in Mixed Matrix Membranes

International audienceAn innovative computational methodology integrating density functional theory calculations and force field-based molecular dynamics simulations was developed to provide a first microscopic model of the interactions at the metal-organic framework (MOF) surface/polymer interface. This was applied to the case of the composite formed by the polymer of intrinsic microporosity, PIM-1, and the zeolitic imidazolate framework, ZIF-8, as a model system. We found that the structure of the composite at the interface is the result of both the chemical affinity between PIM-1 and ZIF-8 and the rigidity of the polymer. Specifically, there is a preferential interaction between the -CN groups of PIM-1 and the NH terminal functions of the organic linker at the ZIF-8 surface. Additionally, the resulting conformation of the polymer gives rise to interfacial microvoids at the vicinity of the MOF surface. The porosity, rigidity, and density of the interfacial polymer were analyzed and compared to those for the bulk polymer. It was shown that the polymer still feels the impact of the MOF surface even at long distances above 15-20 Å. Further, both the polydispersity of the polymer and the flexibility of the MOF surface were revealed to only slightly affect the properties of the MOF/interface. This work, which delivers a microscopic picture of the MOF surface/polymer interactions at the interface, would lead, in turn, to the understanding of the compatibility in MOF-based mixed-matrix membrane

Role of MOF surface defects on the microscopic structure of MOF/polymer interfaces: A computational study of the ZIF-8/PIMs systems

International audienceThe influence of defects at the metal-organic framework (MOF) surface on the microscopic structure of a MOF/polymer composite has been studied by a computational methodology that combines density functional theory calculations with force field-based molecular dynamics simulations. This has been applied to composites formed by ZIF-8 and two different polymers of intrinsic microporosity: PIM-1 and PIM-EA-TB. Analysis of the MOF/polymer interactions, surface coverage, polymer conformation/stiffness and a full characterization of the interfacial voids are provided. We found that, although the nature of the MOF/polymer interactions changes in the presence of defects, the coverage and conformation of the polymer, as well as the morphology of the "interfacial microvoids" remain practically unchanged from a microscopic point of view. These results suggest that there is no microscopic evidence that defective MOF surfaces drastically change the geometry of the MOF/polymer interface and the strength of the physisorption-type interactions in play. (C) 2017 Elsevier Inc. All rights reserved

Putting Forward NUS-8-CO 2 H/PIM-1 as a Mixed Matrix Membrane for CO 2 Capture

International audienc

Derivation of new interatomic potential for flexible metal-organic frameworks: a pre-requisite for understanding swelling under adsorption conditions

International audienc

CO2 adsorption in the hybrid porous MIL-53 (Al) material : A Grand Canonical Monte Carlo simulation compared to Microcalorimetry

International audienc