Hydrophobic Metal–Organic Frameworks: Assessment, Construction, and Diverse Applications

Abstract

Tens of thousands of metal–organic frameworks (MOFs) have been developed in the past two decades, and only ≈100 of them have been demonstrated as porous and hydrophobic. These hydrophobic MOFs feature not only a rich structural variety, highly crystalline frameworks, and uniform micropores, but also a low affinity toward water and superior hydrolytic stability, which make them promising adsorbents for diverse applications, including humid CO2 capture, alcohol/water separation, pollutant removal from air or water, substrate‐selective catalysis, energy storage, anticorrosion, and self‐cleaning. Herein, the recent research advancements in hydrophobic MOFs are presented. The existing techniques for qualitatively or quantitatively assessing the hydrophobicity of MOFs are first introduced. The reported experimental methods for the preparation of hydrophobic MOFs are then categorized. The concept that hydrophobic MOFs normally synthesized from predesigned organic ligands can also be prepared by the postsynthetic modification of the internal pore surface and/or external crystal surface of hydrophilic or less hydrophobic MOFs is highlighted. Finally, an overview of the recent studies on hydrophobic MOFs for various applications is provided and suggests the high versatility of this unique class of materials for practical use as either adsorbents or nanomaterials.

Understanding the Incorporation and Release of Salicylic Acid in Metal‐Organic Frameworks for Topical Administration

“…First, SA is considered a lipophilic and hydrophobic molecule with a partition coefficient (log Pow) at room temperature of 2.26 [38] and therefore, a priori it will be better adsorbed in hydrophobic matrices. Although MOFs possess both a polar part (metal clusters) and a more or less non‐polar fraction (aromatic ligands), from all tested materials, ZIF‐8 is the most hydrophobic material, UiO‐66 and UiO‐66‐NH 2 show a moderate hydrophobicity, MIL‐127 can be considered a hydrophilic/hydrophobic structure, and MIL‐163, MIL‐100, MIL‐53 and MIL‐53‐(OH) 2 could be regarded as more hydrophilic materials [39–41] . These consideration fall mainly in the broad that low SA capacity is reached in hydrophilic MOFs while better total SA cargo is obtained in the hydrophobic ones.…”

Improving Water Stability of Metal–Organic Frameworks by a General Surface Hydrophobic Polymerization

“…It has been well documented that surface hydrophobicity would increase the water stability of MOFs. 26,31,[33][34][35][36][37] In order to examine the water stability of HKUST-1-P, both parent and modified MOF samples were exposed to water for 3 days. HKUST-1 can easily settle down to the bottom of the water owing to its good hydrophilicity (Figure 2c).…”

Polydimethyl siloxane/MIL-101 Composites for Enhanced Toluene Adsorption in the Presence of Humidity

“…An effective VOC adsorbent requires hydrophobicity on both internal pore and external surfaces for optimal organic molecules adsorption. 24 However, the traditional contact angle method only provides the extent of hydrophobicity for the outer surface, but not for the surface of the internal pores. Furthermore, contact angle measurements do not consider factors specific to adsorption performance including differences in size, volume, and shape of the pores.…”