A Roadmap to Sorption-Based Atmospheric Water Harvesting: From Molecular Sorption Mechanism to Sorbent Design and System Optimization

Abstract

Sorption-based atmospheric water harvesting (SAWH), which uses sorbents to capture water vapor from the air and low-grade energy to produce fresh liquid water, has been recognized as a promising strategy for decentralized water supply in arid areas. This review aims to summarize the latest progress in this field and provide perspectives for the further development of SAWH, focusing on the design of sorbent materials and the optimization of the entire system. We first introduce the water sorption mechanisms on different sorbent materials. Next, we discuss the properties and performances of various sorbents developed for SAWH by categorizing them into specific groups: nanoporous solids, hygroscopic polymers, salt-based composites, and liquid sorbents; for each type of sorbent materials, we have analyzed its advantages and limitations, as well as design strategies. In addition, we discuss the influences of the mass and heat transport of the SAWH system on its overall performance in actual operations, and introduce different types of water harvesters developed for SAWH. In the last section, we outline the challenges in this field from fundamental research and practical application aspects, and describe roadmaps for the future development of this technology.

Techno-economic analysis of atmospheric water generation by hybrid nanofluids to mitigate global water scarcity

“…desalination). [48] However, this energy penalty can be mitigated with controlled choice of liquid desiccants, [43], [45], [48] while simultaneously introducing nanomaterials-doped hybrid nanofluids with improved thermal, mechanical, and physical properties. [49], [50] Based on the classical and statistical mechanics, a detailed model was previously developed [51], [52] to correlate the specific heat capacity of a nanofluid 𝐶 𝑝,ℎ𝑓 as a function of nanomaterial volume fraction 𝜑 in the liquid desiccant.…”

“…In general, liquid desiccants such as LiCl possesses surface vapor pressure as low as 0.36 kPa. [45] As air contacts LiCl in the scrubber column, cooling-free water condensation with almost no energy input happens due to a vapor pressure gradient, [35] unlike direct-air cooling techniques that require external energy input to provoke condensation. [45] In addition, liquid desiccants allow the molecules into the bulk volume, where an initial surface capture happens followed by a subsequent internal permeation process.…”

“…[45] As air contacts LiCl in the scrubber column, cooling-free water condensation with almost no energy input happens due to a vapor pressure gradient, [35] unlike direct-air cooling techniques that require external energy input to provoke condensation. [45] In addition, liquid desiccants allow the molecules into the bulk volume, where an initial surface capture happens followed by a subsequent internal permeation process. This mass transfer caused by the vapor pressure gradient will occur until an equilibrium is reached between water in the air and LiCl.…”

“…Dilute LiCl from the scrubber column that is operated adiabatically must be regenerated with external energy input where the internal water molecules continue to diffuse toward the surface by the concentration gradient. [45] A fraction of dilute LiCl is regenerated, allowing it to initially go through HE1 where it is preheated with returning hot regenerated (rich) LiCl to recover the sensible heat. In the second stage, LiCl from HE1 is passed through a two-phase heat exchanger HE2, that functions as a condenser to recover latent heat of condensation from the returning superheated vapor at saturated pressure exiting the isobaric compressor.…”

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

“…And the high water affinity from the charged ions of hygroscopic salts leads to a high energy input demand for water release, severely hindering their applications in AWH. [9,27] Several strategies have been developed to tackle these challenges. The most widely adopted strategy is to use porous matrices (such as silica gel, porous carbon, and metal-organic frameworks (MOFs)) to help the dispersion of salts.…”