| Apr 02, 2025 |
Hydro-sponge captures atmospheric water with 40 percent less energyA porous hydro-sponge made from natural materials efficiently extracts clean water from air using only sunlight. |
| (Nanowerk Spotlight) The atmosphere contains six times more water than all rivers on Earth combined. This vast reservoir has tantalized scientists seeking solutions to global water scarcity, but extracting that moisture efficiently has proven stubbornly difficult. Recent research from Shanghai has produced a material that captures water vapor from air and releases it using 40 percent less energy than previous methods. |
| They publishe their findings in Advanced Functional Materials ("Biomass-Derived Hydro-Sponge for Ultra-Efficient Atmospheric Water Harvesting"). |
| Water shortages affect billions of people globally, with climate change and population growth intensifying the crisis in many regions. While numerous technologies exist to purify contaminated water, providing fresh water in arid locations with no existing water sources presents a different challenge entirely. The air itself offers a potential solution, as even desert environments contain some moisture. |
| Technologies for harvesting atmospheric water have evolved significantly over time. Early systems condensed water by cooling surfaces below the dew point—similar to water droplets forming on a cold glass. These approaches consumed substantial energy and functioned poorly in low-humidity environments. Researchers then developed specialized materials designed to attract water molecules directly from air, but these faced persistent limitations. |
| Metal-organic frameworks (MOFs), crystalline materials with molecule-grabbing properties, showed promise for harvesting water in desert conditions but proved expensive to produce at scale and struggled in fluctuating humidity. Hydrogels—polymers that absorb and retain large amounts of water—performed well in humid environments but collected insufficient moisture in dry conditions. Composite materials combining hydrogels with moisture-attracting salts showed better performance across varying humidity levels but required excessive energy to release captured water. |
| This energy requirement represents a fundamental obstacle. Water molecules tend to form strong hydrogen bonds with the capturing material, making separation energy-intensive. The ideal water-harvesting material would attract moisture readily but hold it loosely enough for easy release. |
| The Shanghai researchers tackled this challenge by creating a material that occupies a middle ground between a hydrogel and a sponge. Their "hydro-sponge," called CPPY, consists of carboxymethyl chitosan (derived from crustacean shells), γ-polyglutamic acid (a natural biopolymer), and polyvinylpyrrolidone, with added polypyrrole to absorb sunlight and generate heat. |
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| Preparation and characterization of CPPY and CPPY@LiCl. a) Schematic diagram of the preparation process of CPPY@LiCl. b) Schematic diagram of the triple network structure of hydro-sponge CPPY (blue dots: intermolecular amide bonds; red dots: molecular lactam bonds; green dots: hydrogen bonds). c) Scanning electron microscope images of CPPY. d) Scanning electron microscope images of CPPY@LiCl. (Image: Reprinted with permssion by Wiley-VCH Verlag) (click on image to enlarge) |
| The team used both chemical and physical foaming techniques to create a highly porous structure with interconnected channels making up 70 percent of the material's volume. This structure allows rapid water movement throughout the material while providing surface area for water molecule attachment. |
| When loaded with lithium chloride, the resulting material (CPPY@LiCl) demonstrated exceptional water uptake across varying humidity conditions: 1.64 grams of water per gram of material at 30 percent relative humidity, 2.65 grams at 60 percent humidity, and 4.21 grams at 80 percent humidity. |
| The key innovation lies in how water exists within the material. Using Raman spectroscopy, researchers identified three distinct water states: bound water (tightly attached to polymer chains), intermediate water (weakly connected), and free water (mobile within pores). CPPY@LiCl contains substantial proportions of intermediate and free water, requiring far less energy for release compared to materials where water forms stronger bonds. |
| This advantage translates to practical benefits. While many water-harvesting materials need temperatures exceeding 80°C to release captured moisture, CPPY@LiCl releases water effectively at just 50°C—achievable using basic solar heating. Measurements showed water in CPPY@LiCl required 40 percent less evaporation energy than pure water. |
| To maximize water production, the researchers implemented a batch processing strategy during outdoor testing. They exposed four CPPY@LiCl units to humid night air, then sequentially heated them during daylight hours using natural sunlight. This approach yielded 6.29 liters of water per square meter daily, with quality tests confirming the water met World Health Organization drinking standards. |
| The material maintained consistent performance through multiple collection cycles, retaining 90 percent capacity even after accelerated aging through UV exposure. The use of biomass-derived components also enhances environmental sustainability compared to synthetic alternatives. |
| This research demonstrates how material design at the molecular level can address critical water-energy challenges. By creating a structure that modifies how water molecules interact with the capturing material, the team achieved both high collection capacity and low-energy release. |
| For water-scarce regions, this technology offers potential for producing clean drinking water using only ambient air and sunlight—no external power required. The materials' effectiveness across varying humidity levels makes it suitable for diverse environments, from arid regions to more temperate climates with seasonal dry periods. |
| Future development will likely focus on further reducing production costs, enhancing durability for long-term outdoor deployment, and optimizing system design for specific climate conditions. While not yet commercialized, this approach represents a significant advance toward practical atmospheric water harvesting systems that could supplement conventional water sources in vulnerable communities worldwide. |
| The researchers emphasize that improving how water molecules interact with sorbent materials offers a promising direction for addressing water scarcity. By reducing the energy barrier for water release, these materials bring us closer to efficiently tapping the atmosphere as a viable freshwater source. |
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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