Approximately one-third of the global population resides in arid and semi-arid regions lacking access to conventional liquid freshwater resources like rivers or shallow aquifers. However, the Earth's atmosphere contains an estimated 13,000 cubic kilometers of water vapor at any given time, maintaining measurable relative humidity (RH) levels even above hyper-arid landscapes such as the Sahara. Harvesting this vapor directly from ambient air and condensing it into potable water without relying on grid electricity represents a frontier in environmental engineering. Atmospheric Water Harvesting (AWH) has emerged as a promising methodology, with engineered aerogel composites serving as high-performance sorption and solar-distillation media.

Conventional sorbents—such as anhydrous inorganic salts, silica gels, or zeolites—encounter severe operational constraints when applied to AWH systems. Solid desiccant grains demonstrate sluggish sorption kinetics and demand high regeneration temperatures, whereas liquid salt solutions undergo swelling, leakage, and corrosion, complicating fluid containment. Aerogels offer high porosities (>90%), massive specific surface areas, and interconnected three-dimensional porous networks, serving as ideal matrices for designing "sorption-desorption" composite systems. By uniformly anchoring hygroscopic salts (such as $text{CaCl}_2$ or $text{LiCl}$) or metal-organic framework (MOF) nanoparticles within the fibrous skeleton of cellulose or synthetic polymer aerogels, the problem of salt solution leakage during deliquescence is resolved.

In these aerogel architectures, the internal nanopores act as microscopic fluid reservoirs. During nighttime periods when ambient relative humidity rises, the hygroscopic salt domain captures moisture from the air, forming a localized liquid phase that remains trapped within the capillary pores of the aerogel matrix via surface tension, preventing macroscopic liquid leakage. During daytime solar exposure, photothermal agents (such as carbon nanotubes or polyphenol networks) embedded on the top surface of the aerogel absorb sunlight and generate localized heat. This thermal energy vaporizes the trapped pore water, which subsequently condenses on an adjacent transparent cover as purified drinking water.

The advantage of the aerogel framework lies in its mass and thermal transport properties. The open, interconnected pore network provides low-resistance pathways for water vapor diffusion, enhancing sorption and desorption kinetics compared to packed-bed sorbents. Concurrently, the intrinsic thermal insulation of the aerogel suppresses downward conductive heat loss into the substrate, concentrating solar thermal energy at the evaporating interface. Operating without external electrical power, these self-sustained, solar-driven aerogel AWH systems convert ambient humidity into drinking water using daily temperature cycles, providing a off-grid water solution for arid communities.