Materials Engineering for Atmospheric Water Harvesting: Progress and Perspectives

Abstract

require substantial centralized infrastructures and frequent maintenance, which can prevent their implementation in some developing or rural areas. [10] Therefore, alternative freshwater generation technologies are necessary, especially in those land-locked nations and arid regions. The ubiquitous atmosphere contains ≈12 900 cubic kilometers of water vapor, which is a valuable source of freshwater. In this regard, extracting water from the air, that is, atmospheric water harvesting (AWH), becomes a promising alternative technology to produce freshwater in the absence of centralized facilities and without regional restrictions. [11,12] AWH can be achieved through three different approaches: fog collection, dew harvesting, and sorbent-based AWH. Fog collection technology directly harvests tiny water droplets in the air without the need of electricity. [13] However, it requires the existence of fog, which is only applicable in coastal or mountainous regions. [14] Another straightforward method to achieve AWH in a broader geographic range is to create the dew point (the temperature at which the air is saturated with water vapor) using dehumidification equipment with cooling components, that is, the dew harvesting. [15] However, cooling the air below its dew point consumes enormous energy and causes low energy efficiency, especially in those hot and dry areas. [16] To overcome these challenges, sorbent-based AWH was developed to spontaneously capture the free water molecules in the air via adsorption or absorption. [17][18][19] The interaction between water and sorbents leads to the cooling-free water condensation. For example, metal-organic framework (MOF)-based materials can capture water molecules from an arid environment with a relative humidity lower than 30% without cooling accessories. [20] To enhance the performance of AWH technologies, it is essential to first understand the fundamental process of AWH. The core of AWH is to extract free water molecules or tiny water droplets from the air and turn them into fresh bulk water, that is, to manage the evolution of water. Specifically, taking advantage of materials engineering tools to tailor the water-materials interactions, various water evolution processes (Figure 1), such as, rapid droplet nucleation (for dew harvesting), fast droplet growth, and efficient droplet departure (for fog/dew harvesting), effective vapor capturing and energy-efficient water release (for sorbent-based AWH), can be realized to facilitate the AWH. For example, the integration of a hydrophilicity-switchable polymer Atmospheric water harvesting (AWH) is emerging as a promising strategy to produce fresh water from abundant airborne moisture to overcome the global clean water shortage. The ubiquitous moisture resources allow AWH to be free from geographical restrictions and potentially realize decentralized applications, making it a vital parallel or supplementary freshwater production approach to liquid water resource-based technologies. Recent advances in regulating chemical properties an...

Prospects for Simultaneously Capturing Carbon Dioxide and Harvesting Water from Air

“…[65,66] Hydrogels have also attracted significant attention as a result of their high water capacities and low regeneration energy, but improvements in stability and absorption/desorption kinetics are still needed. [67][68][69][70] For comprehensive discussion of atmospheric water harvesting technologies, the reader is directed to the following refs. [45,53,60,[70][71][72][73].…”

Tailoring the Desorption Behavior of Hygroscopic Gels for Atmospheric Water Harvesting in Arid Climates

“…[9,10] Atmospheric water harvesting (AWH) is an emerging clean water generation technology promising for decentralized and off-grid water production that can help alleviate the global water shortage. [11][12][13] Dew and fog harvesting approaches are convenient and low-cost AWH technologies. [14][15][16] However, these approaches require either the presence of dense fog or the use of energy-intensive cooling processes, which significantly limits their wide applications in arid and rural areas.…”

Sustainable water generation: grand challenges in continuous atmospheric water harvesting

“…Their mainstream adaptability in AWH is limited by low vapor sorption potential, low thermal conductivity and high regeneration temperatures (>100 °C). 23 Chemical sorbents containing hygroscopic salts, such as LiCl, CaCl 2 and MgCl 2 demonstrate a significantly higher water uptake in a wide range of RH. LiCl has been found as one of the most promising inorganic salts among LiCl, CaCl 2 , MgSO4, and MgCl 2 for AWH applications in an arid climate.…”