Free-standing MOF film with hierarchical porous structure for efficient solar-powered atmospheric water harvesting

Adsorption-based atmospheric water harvesting (AWH) emerges as a new method to solve water scarcity in desolate and arid areas. Due to their designable and adjustable water sorption property, metal–organic frameworks have recently been proposed as the most promising hygroscopic sorbent materials for highly efficient water collecting in solar-powered AWH applications. However, their practical usage is still hindered by their powdery nature and poor photothermal properties, limiting the overall mass and heat transport efficiency. In this work, we prepared a free-standing MOF film with a hierarchical porous structure that simultaneously exhibits a rapid water vapor adsorption rate and excellent photothermal conversion capability. The hierarchical porous structure could provide abundant fast water transport channels and promote longer light-matter interaction paths within the pores. The porous MOF films thus exhibit a water adsorption capacity of 6.13 g m⁻² and an adsorption rate of 8.16 g m^-2h⁻¹ even at a low relative humidity level of 20 %, and it could be solar-heated to 75 ℃ under 1 sun irradiation, which is sufficient to drive the desorption process. This work offers an alternative approach for developing novel monolithic MOF material that integrates water adsorption and photothermal desorption and advancing air–water harvesting technology for application in arid and desert regions and areas with limited power supply.