A Hydrolytically Stable Cu(II)-Based Metal−Organic Framework with Easily Accessible Ligands for Water Harvesting

Water
scarcity is a critical issue in desert and arid regions,
and atmospheric water harvesting is a potential solution. The challenge
is lacking ideal adsorbents that can efficiently capture water from
low-humidity air and be regenerated readily. Herein, we report a hydrolytically
stable metal–organic framework (MOF), [Cu2(AD)2(SA)] (Cu-AD-SA), with excellent performance in water harvesting.
More importantly, this material can be facilely prepared from two
easily accessible ligands adenine (HAD) and succinic acid (H2SA). Cu-AD-SA has a three-dimensional (3D) framework structure with
the crs topology and intersecting channels of ∼5
Å in diameter. The channel surface is decorated by uncoordinated
aromatic N atoms, amine groups, and alkyl moieties. Interestingly,
Cu-AD-SA shows a high water adsorption capacity of 0.16 g g–1 at low pressure of 0.2 P/P0 and 25 °C. Furthermore, dynamic water adsorption–desorption
cycling experiments demonstrated a stable working capacity of 0.13
g g–1 for uptaking water from a low-humidity air
(water partial pressure: 0.85 kPa, 20% RH at 30 °C, 5.3% RH at
55 °C) at 30 °C and desorption at 55 °C. The water
adsorption mechanism was also studied by analyzing its single-crystal
structure after water loading. The results indicated the existence
of strong H-bonding interactions between water molecules and uncoordinated
N atoms and amine groups on the framework, which should play an important
role in the high adsorption at low pressure. All the above features
suggest great potential of Cu-AD-SA for water harvesting in arid regions.