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

Abstract

The adsorption of carbon dioxide and its separation from mixtures with methane using the recently synthetized SIFSIX-2-Cu-i metal-organic framework has been systematically studied by employing a variety of molecular simulation techniques. Quantum density functional theory calculations have been combined with force-field based Monte Carlo and molecular dynamics simulations in order to provide a deeper insight on the molecular-scale processes controlling the thermodynamic and dynamic adsorption selectivity of carbon dioxide over methane, giving particular emphasis on the mechanisms underlying the diffusion of the confined molecules in this porous hybrid material. The diffusion process was revealed to be mainly controlled by both (i) the residence dynamics around some specific interaction sites of the fluorinated metal-organic framework and (ii) the dynamics related to the process where faster molecules overtake slower ones in the narrow one-dimensional channel of SIFSIX-2-Cu-i. We further unveil a 1-dimensional diffusion behavior of both carbon dioxide and methane confined in this small pore MOF where single file diffusion is not observed.

Highly tunable sulfur hexafluoride separation by interpenetration control in metal organic frameworks

“…Well-established all-atom rigid potential models for SF6 [28] and N2 [29] have been selected. The microscopic models for the MOFs, including the force field parameters, were defined following the same strategy than in our previous works [27,30]. More specifically, the CHELPG atomic charges were extracted from cluster-based density functional theory (DFT) calculations [27] while the sigma and epsilon 12-6 Lennard-Jones (LJ) parameters were taken from the literature, the LJ parameters from the DREIDING [31] and the UFF [32] force fields being assigned to the atoms of the organic and inorganic building blocks of the MOF, respectively (see Ref.…”

“…More specifically, the CHELPG atomic charges were extracted from cluster-based density functional theory (DFT) calculations [27] while the sigma and epsilon 12-6 Lennard-Jones (LJ) parameters were taken from the literature, the LJ parameters from the DREIDING [31] and the UFF [32] force fields being assigned to the atoms of the organic and inorganic building blocks of the MOF, respectively (see Ref. 27 for more details). Lorentz-Berthelot combining rules were employed for the LJ interactions between the different atoms of the MOF/guest pairs.…”

“…The independent nets are staggered with respect to one another, significantly reducing the dimension of the one-dimensional square pore channels to 5.15 Å. SIFSIX-2-Cu-i was demonstrated earlier [26] to remain in its pristine interpenetrated form after evacuation of solvent. This material, with a permanent porosity associated with an apparent BET area of 735 m 2 /g, as well as all this family of fluorinated MOFs was shown to be an ideal platform for the selective capture of CO2 over a wide range of mixtures including CO2/CH4, CO2/N2 and CO2/H2 [26,27]. These findings motivated us to perform a computational exploration of the efficiency of this SIFSIX series of materials for the separation of the SF6/ N2 mixtures at ambient conditions, particularly focusing on the impact of the interpenetrated network.…”

Peculiar Molecular Shape and Size Dependence of the Dynamics of Fluids Confined in a Small-Pore Metal–Organic Framework

“…The Journal of Physical Chemistry Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 4 models for CO 2 14 , N 2 15 and CH 4 16 have been selected whereas the force field used to describe MOF-fluid interactions has been taken from our previous study. 17 The employed force fields have been systematically validated in predicting a wide range of properties of the investigated fluids in previous studies 18,19,20 . Trial GCMC runs with another reliable force field (TraPPE) for CO2 21 at 1 bar and 303 K revealed very small changes in the calculated adsorption enthalpy (39.00 kJ/mol for TraPPE and 38.75 kJ/mol for the employed EPM2 14 force field) and very similar deviation from the available experimental value of 35.0 kJ/mol 13 .…”

“…This implies that the choice of the force field for the fluids does not affect the adsorption properties of the investigated MOF. where nij(t)=1 if a specific atom j is within a pre-defined cut-off distance of a second atom i at times 0 and t, and the atom j has only left the cut-off sphere for a period shorter than t* during the time interval [0,t], otherwise n ij (t)=0 17,22 . For t*=∞, we define the intermittent residence correlation function as the self-diffusion coefficients.…”