TY - JOUR
T1 - A transferable model for adsorption in MOFs with unsaturated metal sites
AU - Campbell, Christopher
AU - Ferreiro-Rangel, Carlos A.
AU - Fischer, Michael
AU - Gomes, José R. B.
AU - Jorge, Miguel
PY - 2017/1/12
Y1 - 2017/1/12
N2 - The number of newly discovered Metal-Organic Frameworks is growing exponentially. Molecular simulation is becoming increasingly important to screen large databases of structures and identify potential candidates for challenging gas separations, but such efforts rely on the availability of accurate molecular models that can predict adsorption in a wide range of different MOFs. MOFs with co-ordinatively unsaturated sites (CUS) pose particular problems because standard force fields are unable to describe their specific interactions with certain adsorbates. In this paper, we demonstrate that our previous approach to describe adsorption in open metal sites, based on a combination of classical Monte Carlo simulations and quantum-mechanical Density Functional Theory calculations, is transferable to several Cu-containing MOFs. By fitting the parameters of our model to match adsorption energies of ethylene on HKUST-1 and transferring them to the Cu-paddlewheel units of other MOFs, we have obtained predictions in good agreement with experimental adsorption measurements. Where agreement is not as satisfactory, we show that this can be explained by limited accessibility or diffusion through the pore network. For one particular MOF, UMCM-150, we show that separate parameters need to be used for the Cu-trimer unit, for which the interaction energies with ethylene are much lower than in the Cu-paddlewheel. Overall, our approach demonstrates that the specific CUS interactions in MOFs can be parameterised separately from other interaction types, such as van der Waals, thus opening the way for the development of an accurate and fully transferable force field for this class of materials.
AB - The number of newly discovered Metal-Organic Frameworks is growing exponentially. Molecular simulation is becoming increasingly important to screen large databases of structures and identify potential candidates for challenging gas separations, but such efforts rely on the availability of accurate molecular models that can predict adsorption in a wide range of different MOFs. MOFs with co-ordinatively unsaturated sites (CUS) pose particular problems because standard force fields are unable to describe their specific interactions with certain adsorbates. In this paper, we demonstrate that our previous approach to describe adsorption in open metal sites, based on a combination of classical Monte Carlo simulations and quantum-mechanical Density Functional Theory calculations, is transferable to several Cu-containing MOFs. By fitting the parameters of our model to match adsorption energies of ethylene on HKUST-1 and transferring them to the Cu-paddlewheel units of other MOFs, we have obtained predictions in good agreement with experimental adsorption measurements. Where agreement is not as satisfactory, we show that this can be explained by limited accessibility or diffusion through the pore network. For one particular MOF, UMCM-150, we show that separate parameters need to be used for the Cu-trimer unit, for which the interaction energies with ethylene are much lower than in the Cu-paddlewheel. Overall, our approach demonstrates that the specific CUS interactions in MOFs can be parameterised separately from other interaction types, such as van der Waals, thus opening the way for the development of an accurate and fully transferable force field for this class of materials.
KW - metal-organic frameworks
KW - co-ordinatively unsaturated sites
KW - copper
KW - Monte-Carlo simulations
KW - adsorption separation processes
KW - Cu-paddlewheel
KW - nanoporous
UR - http://pubs.acs.org/journal/jpccck
U2 - 10.1021/acs.jpcc.6b10751
DO - 10.1021/acs.jpcc.6b10751
M3 - Article
SN - 1932-7447
VL - 121
SP - 441−458
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 1
ER -