Adsorption-based atmospheric water harvesting: A review of adsorbents and systems

Atmospheric water harvesting (AWH) has been an appealing prospect for decades to overcome water scarcity in remote areas. Adsorption-based AWH technologies have gained popularity due to their adaptability, and applicability using low-grade heat sources. This study presents up-to-date and future possibilities of adsorbents and systems for adsorption-based AWH. In this review, in-depth advancements in adsorbent materials are compartmentalized into adsorption equilibrium/isotherms, adsorption kinetics, and thermal conductivity. Various systems designs and modifications have been reviewed and classified accordingly. Liquid desiccants i.e., CaCl₂ and LiCl-based AWH systems produced in between 0.63 to 1.0 kg/m/d of water. Recently, metal-organic frameworks (MOFs) are realized as effective adsorbents for AWH. Their excellent hydrophilicity, structural integrity, and tailorable structures can provide water in high and low relative humidity (RH) areas. MOF-841 and MOF-801 yielded maximum adsorption uptakes at 25 °C i.e., 0.5 and 0.3 g/g, respectively. MOF-801 showed an excellent water production of 0.2-0.3 L/kg/d at 5%-40% RH and 20-40°C. MOF-303 delivered ~0.7 L/kg/d at 10% RH and 27^oC. Cr-soc-MOF-1 and MIL-101(Cr) resulted in maximum adsorption uptakes i.e., 1.9 g/g and 1.4 g/g, respectively. Future possibilities regarding these captivating and emerging adsorption technologies are discussed as concluding remarks.