Round-the-clock water harvesting from dry air using a metal−organic framework

Abstract

Harvesting water from the atmosphere is an important process to solve the extreme lack of water resources in arid regions. Adsorption-based atmospheric water harvesting (AWH) takes advantage of solar thermal energy to harvest water from air. This technique is particularly suitable for arid regions characterized by low humidity and an abundance of sunshine. Nonetheless, under low humidity conditions, AWH is highly dependent on water-adsorbing materials exhibiting excellent performance. In this work, a metal–organic framework (MOF), namely [Zn2(bpy)(btec)(H2O)2]·2H2O, also denoted as MWH-1, was investigated for application in water harvesting under low humidity conditions (<20%). Notably, MWH-1 displayed outstanding water and thermal stability. At temperatures of 293–333 K and low pressure, activated MWH-1a exhibited competitive water uptake (relative humidity (RH) = 5%, uptake>200 cm3·cm−3; RH = 10%, uptake>250 cm3·cm−3). This ensured effective water harvesting at high temperatures during the day. In situ powder X-ray diffraction and Fourier-transform infrared analyses confirmed the sensitive water adsorption process of MWH-1a. The X-ray single-crystal study further demonstrated that single-crystal structures could be completely restored following water harvesting. MWH-1 showed good structural stability and enabled water harvesting under low humidity and high temperature conditions. Thus, it has the potential for application in round-the-clock water harvesting in extremely arid regions.