To pull water from air, just shake it off

Millions of people around the world lack access to clean potable water, a problem that is only getting worse with rising temperatures and a growing population. Yet, the atmosphere contains six times more water than all the fresh water in rivers, according to scientists’ estimates. Researchers have developed several sponge-like materials to capture this water vapor from air. But a new ultrasonic device developed by a team from MIT promises to do it 45 times faster using minimal energy.

They presented the concept in the journal Nature Communications. Atmospheric water harvesting systems typically rely on sorbent materials that take up water from air. But they have a difficult time letting that water go because of the bonds between the water molecules and the sorbent material. Today’s systems use the sun or electricity to heat up the sorbents in order to evaporate and release the water.

This takes energy and time. The MIT team came up with the idea of shaking the water off instead using vibrations. They made an ultrasonic device that produces high-frequency vibrations. The device is simple.

At the center is a flat ceramic ring that vibrates when voltage is applied. Surrounding this ceramic ring is an outer ring that is studded with tiny nozzles. The researchers place the water-harvesting sorbent on top of the device. Once the material has sopped up enough water, the device produces ultrasonic waves that loosen the water.

The released water droplets fall through the nozzle and into collection vessels attached to the vibrating ring. The process takes a few minutes instead of tens of minutes or hours needed by heat-based water harvesting systems. “With ultrasound, we can precisely break the weak bonds between water molecules and the sites where they’re sitting,” said the study’s first author Ikra Iftekhar Shuvo in a press release.

“It’s like the water is dancing with the waves, and this targeted disturbance creates momentum that releases the water molecules, and we can see them shake out in droplets.” Unlike solar evaporators, the device does require a power source. But the MIT researchers say that a small solar cell could power the device, which could also act as a sensor to detect when the sorbent is full and then trigger the ultrasonic water collection.

Source: Ikra Iftekhar Shuvo et al. High-efficiency atmospheric water harvesting enabled by ultrasonic extraction. Image by Jörg Künkel from Pixabay