A sponge-like gel made from food scraps and other natural materials can draw moisture from air even in dry conditions. The system, reported in the journal Advanced Materials, provides a sustainable way to produce drinkable water for low cost to address global water scarcity.
Water has become a precious commodity in many parts of the world, a problem getting exacerbated by a warmer world and rising population. One in three people worldwide lack access to safe drinking water, according to the UNICEF and World Health Organization.
But the Earth’s atmosphere contains around 13,000 cubic kilometers of water. That’s more than all the volume of water in the world’s rivers. And even in dry environments, air carries a small amount of moisture. So researchers have been devising clever materials and technologies to harvest this atmospheric water vapor.
Many of the sorbent materials that have been made so far rely on petroleum-derived polymers. Materials scientist and engineer Guihua Yu and colleagues from the University of Texas at Austin wanted to use natural biopolymers. So they made hydrogels from three carbohydrate molecules: cellulose and starch derived from plants, and chitosan, a compound found in crustacean shells.
The researchers added lithium chloride salt to the hydrogel to boost its ability to absorb water. They also added select chemical groups to the hydrogel that improve its water retention and imparts the ability to release the water at lower temperature. Those features make the material more energy-efficient to use for atmospheric water harvesting.
The cellulose-based hydrogel showed the highest water uptake in lab tests. It was also the most efficient, releasing 95% of captured water at 60°C. So the researchers put it to test in a real-world scenario.
They placed it outdoors for six days, over which they alternated between absorption and desorption cycles. Water harvested by the hydrogel during each absorption cycle was evaporated by heating the hydrogel on an electric hotplate at 60°C. The vapors were collected on a glass plate.
Each kilogram of the hydrogel generated 14.19 liters of clean water daily. That is much more than other more expensive sorbents have been able to produce. Previously made sorbents also require higher temperatures to release the water they soak up.
The team is now trying to make the hydrogel on a large scale and are designing real-world device systems for commercialization. “Since this hydrogel can be fabricated from widely available biomass and operates with minimal energy input, it has strong potential for large-scale production and deployment in off-grid communities, emergency relief efforts, and decentralized water systems,” said graduate researcher Yaxuan Zhao in a press release.
Source: Weixin Guan et al. Molecularly Functionalized Biomass Hydrogels for Sustainable Atmospheric Water Harvesting. Advanced Materials, 2025.
Image: based on photo by © Lenka Příhonská| Dreamstime.com
