A new dual-mode material collects clean water from air using either sunlight or compression, offering reliable, energy-free atmospheric water harvesting even in low-light or sunless conditions.
(Nanowerk Spotlight) In many parts of the world, turning on a tap doesn’t guarantee there will be water. In dry regions, remote communities, and places where infrastructure is fragile or aging, freshwater access remains uncertain. As climate pressures intensify and rainfall patterns shift, the gap between water need and water availability continues to grow.
Yet above even the driest landscapes, water vapor is always present in the air. The challenge is not whether it can be collected, but whether it can be done simply, reliably, and without relying on narrow environmental conditions.
Researchers have developed various systems that extract moisture from the atmosphere. Many use materials that absorb water vapor and then release it through heating, often powered by sunlight. These solar-driven methods are passive, energy-efficient, and adaptable to off-grid settings. But their effectiveness depends on steady solar exposure, which is rarely guaranteed.
Humidity levels often peak when sunlight is low. Cloud cover, pollution, and nightfall all undermine performance. In practice, these systems function well only when conditions happen to align.
This limitation stems from a design assumption: that solar heat will always be available to trigger water release. Attempts to extend performance into low-light conditions have included radiative cooling systems that promote condensation by lowering surface temperatures, as well as electrically heated systems that accelerate water evaporation.
Each approach adds complexity. Cooling systems have limited water yield. Electrical systems require external power. What has been missing is a material that works with or without sunlight, one that does not require external energy or fragile components.
A recent study in Advanced Materials (“Solar‐Mechano Symbiosis Dual‐Mode Janus Bioaerogel for Context‐Adaptive Atmospheric Water Harvesting Beyond Solar Reliance”) presents a solution to this longstanding bottleneck. The research team developed a new material that can harvest atmospheric water and release it in two different ways. Under sunlight, it uses photothermal heating to release the absorbed moisture. In low-light conditions, the water can be extracted simply by squeezing the material. This dual-mode function allows it to operate across a wide range of environments and times of day, without the need for complex control systems or energy input.
The material, called a dual-mode Janus bioaerogel (DBJA), is built from two natural polymers: hydroxypropyl cellulose and konjac glucomannan. These are cross-linked to form a lightweight, porous structure that can hold water and recover its shape after compression. To enhance its ability to attract moisture from the air, the researchers incorporated lithium chloride, a hygroscopic salt known for its strong affinity for water vapor. The salt is distributed evenly through the matrix and stabilized by both physical entrapment and chemical interactions.
To create the dual-function behavior, the team added a layer of polypyrrole to one side of the material. Polypyrrole is a conductive polymer that absorbs a broad spectrum of sunlight and converts it into heat. This layer allows the material to release moisture through evaporation when exposed to the sun. The surface is further treated with phytic acid, which improves hydrophilicity and helps anchor the lithium ions in place. The resulting structure has one side optimized for moisture uptake and another for rapid, controlled water release.
Fabrication and design principle of dual-mode Janus bioaerogel (DBJA). a) Distribution map of average relative humidity in part of Asia (2020). b) Monthly surface light hours in landmark cities throughout China. c) Diagram showing the operationmechanism of solar-mechano symbiosis dual-mode AWH for DBJA under different weathers. d) Diagram of the DBJA multi-path moisture absorption. e) Comparative analysis of the performance of DBJA in five areas: solar independence, adsorption, desorption, sustainability, and scalability. (Image: Reprinted with permission from Wiley-VCH Verlag) (click on image to enlarge)
The researchers experimented with different amounts of polypyrrole coverage and found that a 25 percent coating provided the best performance. Higher coverage blocked the pores needed for moisture transfer, while lower coverage did not provide enough heating capacity. The optimized material could absorb more than three grams of water per gram of aerogel under high humidity. Under one-sun illumination, it released 88 percent of the stored water within two hours. Even at reduced light levels, equivalent to cloudy weather, it released 72 percent of the stored moisture.
To evaluate real-world performance, the team tested the material outdoors using a passive chamber designed to collect condensed water. The aerogel was exposed overnight to ambient air, during which it steadily absorbed moisture. As morning sunlight arrived, the chamber was closed and sunlight passed through a slanted glass cover, triggering photothermal heating. The released vapor condensed on the glass and was collected. Over the course of the day, the system harvested 1.32 grams of water per gram of material. This performance held even under partial shade and variable light conditions.
In addition to its solar-driven operation, the material demonstrated a reliable mechanical release mode. When gently compressed by hand, the aerogel released stored moisture without needing heat. A small sample measuring 50 cubic centimeters produced more than 150 milliliters of water after five cycles of compression. The material regained 98 percent of its original volume after each cycle and maintained performance over 50 consecutive uses.
Although some lithium salt loss was observed in early cycles, the release rate dropped to negligible levels after stabilization. Ion concentrations in the collected water remained below World Health Organization drinking water limits.
To further improve water quality, the researchers developed a simple filtration unit using activated carbon and ion exchange resins. This compact device removed excess salts and other ions, resulting in clear, potable water. The entire process requires no electricity and can be carried out using small, portable components.
The aerogel is lightweight, vacuum-packable, and mechanically resilient. Its modular design allows it to be scaled up for larger water needs or used individually in field settings. Because it functions independently of light availability, it avoids one of the most persistent limitations in previous atmospheric water harvesting systems.
This dual-mode approach represents a practical advance in water collection technology. Rather than adding external energy sources or building more complex devices, the researchers focused on rethinking the material itself. By combining solar heating and mechanical compression into a single structure, they have expanded the operating range of atmospheric water harvesters and improved their reliability in variable conditions.
As global demand for decentralized water solutions continues to grow, materials that can function across environmental constraints are likely to play an increasingly important role.
For authors and communications departmentsclick to open
Lay summary
Prefilled posts
Nanowerk Newsletter
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.
