  Sorption of gases in micro- and mesoporous materials is typically interpreted
on the basis of idealized structural models where real structure effects such
as defects and disorder are absent. For covalent organic frameworks (COFs)
significant discrepancies between measured and simulated adsorption isotherms
are often reported but rarely traced back to their origins. This is because
little is known about the real structure of COFs and its effect on the sorption
properties of these materials. In the present work molecular simulations are
used to obtain adsorption isotherms of argon, nitrogen, and carbon dioxide in
the COF-LZU1 at various temperatures. The (perfect) model COF has a BET surface
that is higher than the experimental BET surface by a factor of approximately
1.33, suggesting defects or inclusions are present in the real structure. We
find that the saturation adsorption loading of small gaseous species in
COF-LZU1, as determined from grand canonical Monte Carlo simulations, is also
higher by approximately the same factor compared to the experimental saturation
loading. The influence of interlayer slipping on the shape of the adsorption
isotherm and the adsorption capacity is studied. Comparison between simulation
and experiment at lower loadings suggests the layers to be shifted instead of
perfectly eclipsed. The sensitivity of the adsorption isotherms in this regime
towards the underlying framework topology shows that real structure effects
have significant influence on the gas uptake. Accounting for layer slipping is
important to applications such as catalysis, gas storage and separation.
