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.