(Nanowerk Spotlight) Water scarcity affects billions of people worldwide. While Earth’s oceans hold abundant water, converting seawater into fresh water requires substantial energy and complex infrastructure. Modern desalination plants use processes like reverse osmosis, pushing seawater through specialized membranes under high pressure. These facilities are expensive to build and operate, limiting their use in many regions where clean water is most needed.
Scientists have explored simpler approaches using solar power to evaporate seawater, similar to nature’s water cycle. By concentrating sunlight to heat seawater, these systems produce clean water vapor that can be collected as fresh water. However, solar-powered systems only work during sunny days. Meanwhile, electrical heating methods often waste energy by accidentally splitting water molecules into hydrogen and oxygen instead of just heating the water.
Nature offers an elegant solution to efficient solar absorption through the feathers of birds-of-paradise. These birds possess incredibly dark feathers that can capture nearly all incoming light using microscopic structures that trap light rays, forcing them to bounce around until absorbed. Similarly, common electric kettles use a clever design where the heating element is covered by an insulating layer, preventing electrical current from flowing through the water while still transferring heat effectively.
Drawing inspiration from both these examples, researchers at Donghua University created a new type of water-purifying fabric featuring nanoscale engineering. They started with carbon fibers, excellent conductors of electricity, and grew titanium dioxide (TiO2) nanorods, each only 300–500 nanometers in diameter and 1.5–2.0 micrometers in length. These tiny rod-like structures resemble a microscopic forest and enhance light absorption. They then coated the nanorods with polypyrrole (PPy) nanoparticles, measuring around 100 nanometers in size, to further improve light absorption and photothermal conversion.
The fabric works in two ways. Under sunlight, the nanorod-array structure traps light rays, making them bounce between the rods until absorbed, much like the bird feathers. When powered by electricity, the carbon core heats up while the outer nanoscale TiO2/PPy layer prevents direct electrical contact with water, avoiding energy waste through water splitting. The material captures 95.5% of incoming light, employing nanoscale light-trapping strategies similar to those seen in bird-of-paradise feathers.
Biomimetic design and preparation of the photothermal-electrothermal fabric. a) The array-like feather structure with light-trapping effect from paradise bird. b) The core–shell structure with anti-electrolyzing water ability from electric kettle heating module. c) Scheme of photothermal-electrothermal fabric with array-induced light-trapping effect and the core–shell-structure-induced anti-electrolyzing water ability. d) The preparation process of CF/TiO2/PPy fabric. Photos and SEM images of e–h) CF, i–l) CF/TiO2, and m–p) CF/TiO2/PPy fabrics. (Image: Reprinted with permission by Wiley-VCH Verlag) (click on image to enlarge)
Testing revealed impressive performance. Using only sunlight, the fabric achieved an evaporation rate of 2.2 kg of water per square meter per hour. With electrical power alone, this increased to 7.9 kg/m2/h. When combining both power sources, the system produced 9.1 kg/m2/h, significantly outperforming previous designs.
The researchers solved another critical challenge: salt buildup. Instead of letting water sit still and concentrate salt, they designed the system so water flows along the fabric. The nanoscale surface structure helps maintain continuous movement of saline water across the heated surface, preventing salt crystals from forming and clogging the system. This allows the fabric to run for extended periods without needing cleaning or replacement.
The material maintained consistent performance during 10-hour tests using actual seawater containing various dissolved minerals. This durability in real-world conditions marks a crucial advance over laboratory-only demonstrations. The fabric’s flexibility and relatively simple construction suggest it could be manufactured at larger scales.
This technology offers several advantages over existing approaches. Unlike traditional desalination plants, it requires no high-pressure pumps or complex membrane systems. The ability to use both solar and electrical power means it can operate around the clock and in any weather. The fabric’s flexibility allows it to be shaped into various configurations, while its simple design could keep costs reasonable.
The research demonstrates a practical path toward accessible water purification technology. By combining insights from nature with nanoscale materials and clever engineering, this approach could help address water scarcity in coastal regions, particularly in areas lacking infrastructure for conventional desalination methods. As development continues, this technology could provide a vital tool in the essential task of ensuring clean water access for communities worldwide.
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