(Nanowerk Spotlight) One-third of the global population lacks access to clean water, with the challenge most severe in arid regions that make up 41% of Earth’s land surface. The atmosphere holds vast amounts of untapped water – about 1.3 thousand trillion liters in vapor form. Yet capturing this water efficiently has remained an engineering challenge. Fog collection only works in humid areas, while condensation-based systems consume large amounts of energy for cooling.
Scientists have identified materials that naturally absorb water vapor from air as a promising solution. When heated by sunlight, these materials release their captured moisture as liquid water. This approach, called sorption-based atmospheric water harvesting, can work even in dry conditions without energy-intensive cooling. Certain salts like lithium chloride excel at pulling moisture from very dry air.
However, these salts dissolve and clump together during use, quickly becoming ineffective. Researchers have tried embedding the salts in various porous materials to maintain their performance, but existing solutions either leak salt over time or require complex manufacturing.
A team at Donghua University has now developed a simple yet effective method to create stable salt-containing sponges that overcome these limitations. Their innovation lies in using dopamine – a compound similar to those that give skin its color – to chemically bind lithium chloride salt molecules to a melamine sponge. This creates a three-dimensional interconnected porous structure that maintains the salt’s water-absorbing capabilities without leakage or clumping. The researchers added carbon nanotubes throughout this structure to help the material convert sunlight into heat more efficiently while maintaining the porous network essential for water transport.
Atmospheric water harvesting (AWH) performance of LiCl/PMS/CNTs. a) 5 cycles of water harvesting in 24 hours under simulative arid conditions (30 °C, 30% RH). The whole process was designed as follows: A long cycle for 12 h absorption and 3 h desorption, 3 cycles (1 h absorption and 1 hour desorption), and 1 cycle (1 hour absorption and 2 hours desorption). All the desorption process was conducted under 1.0 sun irradiation. The areas with and without light blue shade represent absorption and desorption processes, respectively. b) The accumulative water production under one day and volume of water collected under each cycle measurement of the device at ambient RH on August 2, 2023, in Shanghai, China. c) Comparison of the water production rate for this device with that of other work. d) Measured ions concentrations, TOC, and TN of the collected water sample. (Image: Reprinted with permission by Wiley-VCH Verlag) (click on image to enlarge)
The resulting material demonstrates exceptional performance across a range of humidity conditions typical of arid regions. At just 15% relative humidity – drier than most deserts – the sponge absorbs 1.26 grams of water per gram of material. This increases to 1.81 grams at 30% humidity and 3.13 grams at 60% humidity. The absorption happens rapidly, with rates reaching 1.36 grams per gram per hour in the first hour at 30% humidity. The interconnected porous structure allows both rapid water vapor absorption and efficient release.
When exposed to sunlight equivalent to a bright day (1.0 sun), the material releases 90% of its captured water in just 70 minutes – significantly faster than previous salt-based materials. In practical testing, a simple device using this sponge produced 3.47 kilograms of water per kilogram of material daily under simulated desert conditions (30 °C, 30% relative humidity). Analysis showed the collected water meets World Health Organization quality standards. Importantly, the material maintained consistent performance over 35 absorption-desorption cycles, demonstrating its stability for long-term use.
The team made their system even more valuable for remote areas by capturing heat generated during both water absorption and release. As the sponge pulls moisture from the air, its temperature rises by about 11 °C due to the chemical reaction. During solar-driven water release, even higher temperatures are achieved. Instead of wasting this heat, they attached a thermoelectric module – a device that converts temperature differences into electricity. The dual-function system generates power during both phases: 35.4 milliwatts per square meter during water absorption and up to 454.4 milliwatts per square meter during solar-driven water release.
The key advance lies in the manufacturing approach. Previous attempts to combine salts with porous materials relied on physically trapping the salt particles. The new method creates chemical bonds between the salt and the sponge using dopamine as a bridge. These bonds prevent the salt from moving or clumping while maintaining its ability to interact with water vapor. The resulting three-dimensional structure, with its network of interconnected pores, enables both rapid water uptake and efficient solar-driven release – achieving better performance than more complex manufacturing methods.
The combination of stable performance, high water production in very dry conditions, and supplementary power generation makes this technology particularly promising for remote arid regions. The straightforward manufacturing process suggests potential for scaling up production at reasonable cost. The material’s ability to produce significant amounts of clean water using only sunlight, while generating electricity as a bonus, represents an important step toward addressing water scarcity in the world’s driest regions.
Get our Nanotechnology Spotlight updates to your inbox!
Thank you!
You have successfully joined our subscriber list.
Become a Spotlight guest author! Join our large and growing group of guest contributors. Have you just published a scientific paper or have other exciting developments to share with the nanotechnology community? Here is how to publish on nanowerk.com.
