| Feb 19, 2025 |
New biomass hydrogels harvest water from air with record efficiency |
| (Nanowerk Spotlight) Earth’s atmosphere holds over 13,000 cubic kilometers of water vapor, yet converting this vast resource into drinkable water remains an engineering challenge. One in three people lack access to safe drinking water, highlighting the urgent need for efficient water harvesting technologies. |
| Scientists have tried various approaches to capture atmospheric moisture. Metal-organic frameworks can quickly absorb and release water but prove too expensive for widespread use. Salt-based materials absorb substantial amounts of water but degrade over time. Synthetic polymer hydrogels effectively capture water but depend on petroleum-based chemicals, contributing to growing environmental concerns as polymer production threatens to consume 20% of global oil production by 2050. |
| Nature offers promising alternatives in three abundant materials: cellulose, the rigid molecule that forms plant cell walls; starch, the energy storage compound in food crops; and chitosan, derived from crustacean shells. These polysaccharides – naturally occurring sugar-based molecules – make up more than 90% of Earth's carbohydrate mass. While each has a different molecular structure and natural function, they share a common limitation: their tightly packed molecules resist water absorption and release. |
| Researchers at the University of Texas at Austin have developed a two-step chemical process that transforms these natural materials into efficient water harvesters. Their modified cellulose-based hydrogel absorbs 1.32 grams of water per gram of material at 30% relative humidity – significantly exceeding the capacity of many synthetic hydrogels. |
| Deatils of these findings have been published in Advanced Materials ("Molecularly Functionalized Biomass Hydrogels for Sustainable Atmospheric Water Harvesting"). |
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| Molecular functionalization strategy of natural polysaccharides as hydrogel sorbents. Molecular functionalization of natural polysaccharides, derived from abundant biomass, enhances their water uptake and lowers the desorption temperature, activating them as SAWH sorbents. At room temperature, the hydrogel absorbs moisture and swells, representing the water sorption state (blue swollen hydrogel, upper right). Upon heating, hydrophobic interactions among the thermoresponsive groups dominate, causing the hydrogel network to contract and transition to the water release state (red contracted hydrogel, bottom right). (Image: Reprinted with permission by Wiley-VCH Verlag) (click on image to enlarge) |
| The transformation process attaches two types of molecular groups to the natural polymers. Temperature-sensitive groups act as molecular switches, triggering water release at 60 °C – achievable with solar heating or waste industrial heat. Zwitterionic groups, containing both positive and negative charges, help maintain water absorption even when the material contains water-attracting salts. |
| The modification process proved effective across all three natural materials, each offering unique advantages. Starch-based hydrogels, benefiting from their naturally looser molecular structure, absorbed 0.89 grams of water per gram at 30% humidity. Chitosan-based versions captured 1.09 grams, with their amino groups enhancing water-binding capacity compared to cellulose and starch. All versions released more than 95% of their captured water when heated. |
| Outdoor testing in Austin, Texas demonstrated the technology's practical potential. A bulk cellulose-based hydrogel collected 726 milliliters of water over six days using overnight moisture capture and daytime heat release cycles. When the team tested smaller pieces of the same material, allowing faster cycling, water production soared to 14.19 kilograms per kilogram daily – among the highest rates reported for atmospheric water harvesting. |
| Several factors contribute to the technology’s economic viability. The modification process scales efficiently, with researchers successfully producing hundreds of grams of modified material in single batches. The abundant raw materials and straightforward chemical modifications keep production costs low. Analysis shows that scaled-up systems could compete with bottled water prices within a year of operation. |
| The collected water easily meets World Health Organization drinking water standards, containing only trace impurities. Several paths could further improve performance: engineering the material's pore structure could accelerate water capture and release; adding heat-conducting materials could improve energy efficiency; incorporating light-absorbing particles could enable direct solar heating. |
| This advancement in sustainable water harvesting arrives as climate change and population growth intensify global water scarcity. The ability to extract clean water from air using modified versions of Earth's most abundant natural materials offers a promising solution to one of humanity's most pressing challenges. |
By
Michael
Berger
– Michael is author of four books by the Royal Society of Chemistry:
Nano-Society: Pushing the Boundaries of Technology (2009),
Nanotechnology: The Future is Tiny (2016),
Nanoengineering: The Skills and Tools Making Technology Invisible (2019), and
Waste not! How Nanotechnologies Can Increase Efficiencies Throughout Society (2025)
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Nanowerk LLC
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