Hydrophobic Metal–Organic Frameworks

Metal–organic frameworks (MOFs) have diverse potential applications in
catalysis, gas storage, separation, and drug delivery because of their nanoscale
periodicity, permanent porosity, channel functionalization, and structural
diversity. Despite these promising properties, the inherent structural features
of even some of the best-performing MOFs make them moisture-sensitive and
unstable in aqueous media, limiting their practical usefulness. This problem
could be overcome by developing stable hydrophobic MOFs whose chemical
composition is tuned to ensure that their metal–ligand bonds persist even in
the presence of moisture and water. However, the design and fabrication of
such hydrophobic MOFs pose a significant challenge. Reported syntheses of
hydrophobic MOFs are critically summarized, highlighting issues relating to
their design, characterization, and practical use. First, wetting of hydrophobic
materials is introduced and the four main strategies for synthesizing
hydrophobic MOFs are discussed. Afterward, critical challenges in quantifying
the wettability of these hydrophobic porous surfaces and solutions to these
challenges are discussed. Finally, the reported uses of hydrophobic MOFs in
practical applications such as hydrocarbon storage/separation and their use
in separating oil spills from water are summarized. Finally, the state of the art
is summarized and promising future developments of hydrophobic MOFs are
highlighted.