High-performance solar-driven water harvesting from air with a cheap and scalable hygroscopic salt modified metal–organic framework

Atmospheric water harvesting (AWH) using solar–driven desorption systems is a viable solution to water shortage in arid regions. However, common water adsorbents, such as zeolite and silica gel, exhibit low water uptake under low relative humidity (RH ≤ 30%) or require high regeneration temperature (≥200 °C), which limits their application in water harvesting. The existing water harvesting metal–organic frameworks (MOFs) exhibit low water uptake at low RH and require high modification cost. Herein, a hygroscopic salt–modified MOF (CaCl2@MOF-808-11.8) is developed to overcome the shortcomings of its respective components. This composite exhibits excellent water uptake of 0.56 g g−1 under low RH (RH = 30% at 25 °C), which is seven times that of MOF-808. The water uptake at low RH, structural stability, and cyclic performance of the material are greatly improved. The performance comparison and simulation results show that CaCl2@MOF-808-11.8 has outstanding water harvesting performance under low humidity. An outdoor water harvesting experiment using a home–made device shows that CaCl2@MOF-808-11.8 can collect 1.8 kg of water per each kilogram of material daily using only a solar–driven power supply system, which is superior to most reported water harvesting MOFs. The cost, hydrophilicity and practical recycling properties of the composite material suggest that it is a very promising material for water harvesting.