Adsorption in porous materials plays a significant role in industrial separation
processes. Here, the host-guest interaction and the pore shape influence the
distribution of products. Metal-organic frameworks (MOFs) are promising materials
for separation purposes as their diversity due to their building block synthesis from
metal corners and organic linker gives rise to a wide range of porous structures. The
selectivity differs from MOF to MOF as the size and shapes of their pores are
tuneable by altering the organic linkers and thus changing the host-guest interactions
in the pores.
Using mainly molecular simulation techniques, this work focuses on three types of
separations using MOFs. Firstly, the experimental incorporation of calixarenes in
MOFs as a linker to create additional adsorption sites is investigated. For a mixture
of methane and hydrogen, it is shown that in the calixarene -based MOFs, methane
is adsorbed preferentially over hydrogen with much higher selectivities compared to
other MOFs in the literature. Remarkably, it was shown that extra voids created by
calixarene -based linkers, were accessible to only hydrogen molecules. Secondly,
the strong correlation between different pore sizes and shapes in MOFs and their
capabilities to separate xylene isomers were investigated for a number of MOFs.
Finally, the underlying molecular mechanism of enantioseparation behaviour in a
homochiral MOF for a number of chiral diols is presented. The simulation results
showed good agreement with experimental enantioselectivity values. It was observed
that high enantioselectivity occurs only at high loadings and when a perfect match in
terms of size and shape exists between the pore size and the adsorbates.
Ultimately, the information obtained from molecular simulations will further our
understanding of how network topology, pore size and shape in MOFs influence their
performance as selective adsorbents for desired applications.