Diffusion of Xylene Isomers in the MIL-47(V) MOF Material: A Synergic Combination of Computational and Experimental Tools

Abstract

The dynamics of xylene isomers in the metal−organic framework MIL-47(V) has been investigated by combining molecular dynamics (MD) simulations and experimental tools including quasielastic neutron scattering (QENS) and deuterium nuclear magnetic resonance ( 2 H NMR).The experimental and simulated self-diffusion coefficients (D s ) values for each single component isomer are in reasonable agreement in the whole range of temperatures. More interestingly, the simulations predict a nonmonotonous evolution of D s with the temperature for all xylenes. Such an unusual trend is experimentally confirmed for p-xylene. Two distinct diffusion regimes are elucidated at the microscopic level: a low-temperature regime where the xylene molecules are close to the MIL-47(V) pore wall with a high activation energy barrier for the diffusion and a hightemperature regime where the xylene molecules are mainly located in the center of the channel associated with a lower activation energy for the diffusion. This dynamic behavior remains also true whatever the degree of pore filling. It has been further shown that the diffusivity is only slightly affected when one compares the case of xylenes in single component and in mixture. 2 H NMR experiments enlighten that packing effects and guest−guest interactions are crucial when considering the dynamics of confined xylenes in MIL-47(V).

CO2 Capture Using the SIFSIX-2-Cu-i Metal–Organic Framework: A Computational Approach

“…The analysis of the trajectory obtained from the MD simulations of the adsorbed CO 2 -CH 4 mixture at 1 bar and 303 K allowed us to extract the self-diffusion coefficients of CO 2 and CH 4 for the system containing 349 CO 2 and 16 CH 4 molecules using the well-known Einstein relation applied to the mean-square displacements for both guests averaged over all the MD trajectories and using a multi-time step origin. [43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59] This led to Ds ( Previous studies revealed the strong interrelation between the self-diffusion of confined molecules and the residence dynamics related to the adsorbent-adsorbate interactions. 79,80 These findings motivated us to further investigate the effect of these interactions on the selfdiffusion of CO 2 .…”

“…Particular emphasis was placed on the mechanisms underlying the diffusion of molecules in confined pores of the hybrid material using Molecular Dynamics, a strategy that we have intensively applied over the last decades to explore the diffusion of a series of gases in various MOFs. [43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59]…”

Flexible Metal–Organic Frameworks: Recent Advances and Potential Applications

“…Besides the flexible behavior of the framework structure, the diffusion and arrangement of guest molecules in the pores/channels of flexible MOFs is another hot topic for theoretical investigations, since guest related applications, for example, drug delivery and guest capture/release, deeply rely on the understanding of these phenomena. A series of work by Maurin and co‐workers focused on the behaviors of different guests, such as H 2 S, H 2 O, xylene isomers, CO 2 /CH 4 mixtures, and light hydrocarbons, in the MIL family of MOFs. Combining the experimental results and molecular dynamics (MD) simulations, the state of guest molecules in the channels of MOFs could be revealed, which helped in determining the critical host–guest interaction factors and the conditions for desired applications.…”

In Operando Analysis of Diffusion in Porous Metal‐Organic Framework Catalysts

“…[33] For large crystals of Cu 3 btc 2 (btc = 1,3,5-benzenetricarboxylate, HKUST-1) (0.7, 1.0 and1 .3 mm) the diffusivity of CO 2 differed in the range of 0.0014-0.0020 mm 2 s À1 with crystal size. [19c] Experimental conditions:I na ddition to factorsr elated to the structure of the porousm aterial and the specific sorbate of interest, diffusion kinetics are also influenced by experimental conditions such as temperature, [34] the concentration/loading of the sorbate, [28,35] and the orientation of crystallites with respect to the sorbate solution. [36]…”