Gate-Opening Mechanism of Hydrophilic–Hydrophobic Metal–Organic Frameworks: Molecular Simulations and Quasi-Equilibrated Desorption

Adsorption of polar and nonpolar
molecules in hydrophilic–hydrophobic
STAM-1 metal–organic framework was studied by means of quasi-equilibrated
temperature-programmed desorption and adsorption (QE-TPDA) experimental
technique and molecular simulation. The QE-TPDA measurements revealed
that thermal stability of the studied material in the presence of
water may be lower than determined from thermogravimetric analysis.
Molecular dynamics showed evident impact of diffusion on the adsorption
mechanism in STAM-1. The QE-TPDA profiles recorded for adsorption
of n-alkanes, water, and alcohols indicate the gate-opening
effect occurring only upon adsorption of polar molecules, which was
confirmed by in situ IR spectroscopy. Monte Carlo molecular simulations
agree with experimental data revealing preferable adsorption sites
for the molecules of alcohols in STAM-1. Simulations also showed that
the molecular mechanism of the gate-opening is dependent on the size
of polar guest molecules.