What makes zeolitic imidazolate frameworks hydrophobic or hydrophilic? The impact of geometry and functionalization on water adsorption

Abstract

We demonstrate, by means of Grand Canonical Monte Carlo simulation on different members of the ZIF family, how topology, geometry, and linker functionalization drastically affect the water adsorption properties of these materials, tweaking the ZIF materials from hydrophobic to hydrophilic. We show that adequate functionalization of the linkers allows one to tune the host-guest interactions, even featuring dual amphiphilic materials whose pore space features both hydrophobic and hydrophilic regions. Starting from an initially hydrophobic material (ZIF-8), various degrees of hydrophilicity could be obtained, with a gradual evolution from a type V adsorption isotherm in the liquid phase to a type I isotherm in the gas phase. This behavior is similar to what was described earlier in families of hydrophobic all-silica zeolites, with hydrophilic "defects" of various strength, such as silanol nests or the presence of extra-framework cations.

Structural single and multiple molecular adsorption of CO 2 and H 2 O in zeolitic imidazolate framework (ZIF) crystals

“…However, according to these new results, one water molecule adsorbed per unit cell presents E ads of -4.78 and -8.40 kcal/mol in ZIF1 and ZIF4, that it is in the order of first adsorbed water molecule in other ZIFs [44]. This can predict the existence of a possible weak adsorbent-adsorbate interaction (cf.…”

“…Imidazolate Frameworks are hydrophobic [3,41], although some of them, such as ZIF90, show a water uptake at around P/P 0 ≈ 0.4, or show, such as ZIF8 [42], reversible intrusion-extrusion cycles for liquid water in the 15-35 MPa range, or a shock-absorbing behaviour as ZIF7 which is believed to be highly hydrophobic solid [43].…”

Underlying Adsorption Mechanisms of Water in Hydrophobic and Hydrophilic Zeolite Imidazolate Frameworks: ZIF-71 and ZIF-90

“…This correspondence between the RDFs lead one to conclude that the structure of water adsorbed in the ZIF pores at saturation is similar to bulk liquid water. 32 This result is reasonable taken the large pore sizes of the ZIFs into account. The large available space allows a large number of neighboring water molecules promoting hydrogen bonding.…”

Molecular Mechanism of Swing Effect in Zeolitic Imidazolate Framework ZIF‐8: Continuous Deformation upon Adsorption

“…[61] The ZIF-8 structure was described as in Ref. [62].T hese force field parameters are presented in the Supporting Information. Lorentz-Berthelot rules were used to calculate ZIF-N 2 Lennard-Jones parameters.…”