A novel hygroscopic salt-modified MOF-303 with efficient solar-driven water harvesting from arid air†

Abstract

Water scarcity has become one of the greatest crises in the world, especially for people living in arid areas. Among all water sources, atmospheric water has the advantages of fewer geographical limitations and a lower environmental impact during the water production process. The use of solar-powered atmospheric water harvesting (AWH) has become a viable solution to the problem of water scarcity in arid regions. MOF-303 is a robust and water-stable MOF that collects water at low relative humidity (RH ≤ 30%) and releases it under mild heating. However, its actual demonstrated water absorption remains unsatisfactory, which limits its application in the field of water harvesting. Here, we propose a high-performance composite adsorbent made from a hygroscopic salt-modified MOF and obtain the composite adsorbent MOF-303@LiCl by confining LiCl in the pores of MOF-303. The composite adsorbent exhibited excellent water absorption of 0.61 g g⁻¹ at low relative humidity (25 °C, 30% RH) and high adsorption kinetics (adsorption saturated at 80 min). By adding a certain proportion of the photothermal material CB, MOF-303@LiCl could be heated up to 66.1 °C under one solar irradiation, achieving desorption within 60 min. The adsorption–desorption cycle of this composite adsorbent can be powered by natural sunlight without the need for optical focusing and additional energy input. The fast adsorption–desorption kinetics allow for multiple cycles of AWH in a single day, which has great potential in water harvesting.