Abstract
Water scarcity, a critical global challenge, has intensified due to the adverse effects of climate change on ecosystems and its detrimental impact on human activities. Addressing this issue requires solutions capable of providing clean water in regions facing hydroclimatic challenges and limited infrastructure. Atmospheric water harvesting (AWH) offers a promising solution, particularly in arid regions, by extracting moisture from the air. This review explores AWH technologies that leverage material porosity and hygroscopicity, focusing on highly porous materials such as Metal-Organic Frameworks (MOFs) and monolithic scaffolds. While MOFs exhibit exceptional water uptake due to their tunable chemistry and nanoscale porosity, their powdery nature poses stability and processability challenges. To overcome these limitations, integrating MOFs into multiscale porous monoliths-such as foams, aerogels, cryogels, and xerogels-enhances structural integrity and performance. The role of hierarchical porosity, engineered across nano-scale in MOF (<2 nm) and micro-scales (>2 nm) is emphasized in porous monoliths, in optimizing water capture efficiency. This review also highlights recent advancements in MOF-based composite monoliths, their working mechanisms, and the potential for large-scale implementation. By integrating nanotechnology with material chemistry, this work outlines strategies to enhance sorption capacity, desorption kinetics, and scalability, ultimately providing a roadmap for developing efficient, sustainable, and scalable AWH systems.