Researchers have developed a solar-powered, sponge-like aerogel that converts saline seawater into drinkable water, marking a significant step towards sustainable desalination. The apparatus requires nothing other than sunlight and a plastic cover. Previous materials failed to maintain efficiency at a large scale. On the other hand, this 3D-printed material has been able to maintain its efficiency at larger sizes, thereby solving scalability issues. In outdoor tests, the sponge-like material produced clean water from the ocean without any electricity. This success points to a low-cost, energy-free method for producing freshwater from seawater.
Most of Earth’s water is present in oceans and is too salty to drink. Desalination is a process by which seawater is turned into potable water. However, the process requires large amounts of energy. Now, researchers have developed a sponge-like material with long, microscopic air pockets that use sunlight and a plastic cover to turn seawater into fresh, drinkable water.
This is not the first instance of a spongy material that uses sunlight as a sustainable source for desalinating water. Previously, a loofah-inspired hydrogel with polymers inside its pores was tested on chromium-contaminated water. When heated by the sun, the hydrogel releases collectible, clean water vapor through evaporation. While hydrogels are liquid-filled, aerogels are rigid and have solid pores that can transport liquid water or water vapor. Aerogels have been tested as a viable option in desalination, but their evaporation performance has been limited. Usually, with increasing size of the material, the evaporation performance declines. So, Xi Shen and colleagues planned to design a porous desalination aerogel that maintained its efficiency at various sizes.
The scientists created a paste from carbon nanotubes and cellulose nanofibers. Then, the researchers 3D printed the paste on a frozen surface, allowing each layer to solidify before adding the next. Through this process, the scientists created a sponge-like material with evenly distributed tiny vertical holes, each 20 micrometers wide. Various sizes of the material, from 0.4 inches to 3 inches, were tested. In their experiment, the scientists found that the material with larger sizes was as efficient in releasing water through evaporation as the smaller ones.
In an outdoor test, the researchers placed the spongy material in a cup containing seawater and covered it with a curved, transparent plastic cover. Sunlight heated the top of the material, leading to evaporation of just water and not the salt. The water vapor then condensed on the plastic cover, and the collected clean water was then moved to the edges. Here, the clean water dripped into a funnel and a container below the cup. After exposure to six hours of sunlight, the apparatus managed to produce three tablespoons of potable water.
“Our aerogel allows full-capacity desalination at any size,” Shen says, “which provides a simple, scalable solution for energy-free desalination to produce clean water.”
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