Multiscale modeling of metal-organic frameworks

Metal-organic frameworks (MOFs) are hybrid nanoporous materials that have been studied intensively due to their potential in a plethora of applications, such as CO2 and hydrogen storage, sensor devices, catalysis and adsorptive separations. MOFs containing open-metal sites are more reactive towards olefins as compared to paraffins and are therefore potential sorbent materials for adsorptive separations of olefin/paraffin mixtures. The underlying molecular orbital interactions at the open-metal site play an essential role in these adsorption processes. In the first part of this thesis, ab initio molecular orbital theory is used to elucidate the electronic interactions of water and ethylene at the open-metal site. The energetics resulting from the associated orbital interactions is incorporated in the grand-canonical Monte Carlo simulations as an additional force field potential. This is essential to make accurate predictions of the multicomponent adsorption behaviour of olefin/paraffin mixtures since, as demonstrated in this thesis, the widely accepted ideal adsorbed solution theory breaks down for olefin/paraffin mixtures in open-metal site MOFs. The second part of this thesis discusses framework flexibility and thermomechanical properties of MOFs. Although MOFs have matured over the last two decades, their industrial breakthrough remains lacking. A key reason for this is their low mechanical stability. Flexible force field models are reviewed and a new parameterization scheme is presented that fits flexible force fields on the ab initio calculated elastic tensor. Variable-temperature nanoindentations combined with molecular dynamics simulations suggest that temperature has a substantial effect in destabilizing MOFs.