Can you desalinate seawater

Desalinate sea water with sunlight

Coastal states that suffer from drought, such as Israel, are increasingly relying on the desalination of seawater. However, the conventional, large systems require a lot of energy to extract the salt from the water. Scientists are now proposing to use sunlight directly for desalination. In the journal “Nature Photonics” they present a nanoporous material made of aluminum that has shown high efficiency in the laboratory and could lead to small and very cheap desalination plants.

Porous nanostructures

"In contrast to other desalination methods, our module is small, portable and suitable for personal water supply," says Jia Zhu from Nanjing University in China. Together with his colleagues, he treated a thin aluminum foil with phosphoric acid. This created a highly porous layer with openings that were smaller than a third of a micrometer. They deposited aluminum nanoparticles on this layer, which also oxidized to aluminum oxide on their surface.

This black material was so light that it could swim effortlessly on salt water. It absorbed incident sunlight very efficiently and achieved a high degree of absorption of more than 96 percent of the solar spectrum. Locally, it quickly heated up to 80 to almost 100 degrees Celsius and increased the rate of evaporation of the water. The steam was able to condense in a small chamber, and potable water with a very low salt content dripped into a reservoir. The researchers made so-called plasmons, which were created on the nanoparticles in the porous aluminum layer when sunlight fell, responsible for the efficient conversion of solar radiation into heat.

Seawater desalination

The first attempts with small, handy desalination plants were successful. Under four-fold concentrated sunlight, almost six liters of water per square meter evaporated every hour. For comparison: Without the porous aluminum layers, less than half of the water evaporated. In their experiments, the researchers used water samples with different proportions of salt between one and ten percent, depending on the salt content of the Baltic Sea or the Dead Sea. The evaporated and then condensed water showed very low salt content in all cases and was suitable as drinking water.

Based on these experiments, small mobile desalination modules could now be developed that could be used with the nanoporous aluminum layers for a decentralized drinking water supply. However, the modules only worked for about 25 evaporation cycles. But the longevity of the layers should be increased in the future. Since the materials used are cheaply available, the researchers can then envision a broad application of their desalination method for private use.