Pioneering solar technology turns air into water

The breakthrough in solar water harvesting uses an innovative gel and system design to efficiently extract water from the atmosphere. This technology could revolutionize access to water in arid, sunny regions, meeting critical needs for drinking water and other uses. (Artist’s concept.) Credit: SciTechDaily.com

The Atmospheric Water Harvester provides water to dry communities using hygroscopic gel and salts.

More than 2.2 billion people currently live in water-scarce countries, and the UN estimates that 3.5 million die each year from water-related diseases. Because the areas most in need of improved drinking water are also located in some of the sunniest places in the world, there is strong interest in harnessing sunlight to help provide clean water.

Researchers at Shanghai Jiao Tong University in China have developed a promising new solar-powered atmospheric water harvesting technology that could help provide enough drinking water for people to survive in these harsh, arid regions. They published their work in Reviews of Applied Physicsa magazine of AIP Publishing.

“This atmospheric water harvesting technology can be used to augment daily water supply needs, such as household drinking water, industrial water and water for personal hygiene,” said author Ruzhu Wang.

Overcoming traditional challenges

Historically, researchers have faced challenges in injecting salt into hydrogels because higher salt content reduces the swelling ability of the hydrogel due to the salting-out effect. This resulted in salt leaching and the water absorption capacity decreased.

“We were impressed that even when up to 5 grams of salt were injected into 1 gram of polymer, the resulting gel maintained good swelling and salt-trapping properties,” Wang said.

Atmospheric water collection cycle during the day

Schematic diagram of the diurnal cycle of atmospheric water collection. Credit: Wang Ruzhu

Innovative hygroscopic gel and system design

Researchers have synthesized a super hygroscopic gel using plant derivatives and hygroscopic salts that is capable of absorbing and retaining an unparalleled amount of water. One kilogram of dry gel can adsorb 1.18 kilograms of water in dry atmospheric environments and up to 6.4 kilograms in humid atmospheric environments. This hygroscopic gel was simple and inexpensive to prepare and would therefore be suitable for large-scale preparation.

In addition, the team adopted a prototype with desorption and condensation chambers configured in parallel. They use a turbofan in the condensation chamber to increase the recovery of desorbed water to more than 90%.

In an outdoor demonstration of a prototype, the team found it released adsorbed water even in the morning or afternoon when the sun was weak. The system can also achieve simultaneous adsorption and desorption during the day.

Future applications and optimizations

The team will work to achieve simultaneous adsorption and desorption using renewable energy to maximize daily water yield per unit mass of adsorbent to further optimize system performance for practical applications in water production.

In addition to everyday water production, sorbent materials that collect atmospheric water may also play an important role in future applications such as dehumidification, agricultural irrigation, and thermal management for electronic devices.

Reference: “Daytime Air-Water Harvesting Based on Super-Hygroscopic Porous Gels with Simultaneous Adsorption-Desorption” by Chengjie Xiang, Xinge Yang, Fangfang Deng, Zhihui Chen, and Ruzhu Wang, 5 Dec 2023, Reviews of Applied Physics.
DOI: 10.1063/5.0160682

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