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

TL;DR

This study uses simulations to show how topology, geometry, and linker functionalization influence water adsorption in ZIFs, enabling tuning from hydrophobic to hydrophilic properties and creating dual amphiphilic materials.

Contribution

It demonstrates how functionalization and topology can be used to control water adsorption properties in ZIFs, introducing dual amphiphilic materials.

Findings

Functionalization tunes host-guest interactions.

Gradual transition from hydrophobic to hydrophilic behavior.

Water adsorption behavior resembles that of hydrophilic zeolites.

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.