New and effective device to extract water from the air

Clean, safe water is a limited resource, and its availability depends on local water bodies. However, the Earth’s atmosphere contains a colossal amount of fresh water in the form of vapor, although, unfortunately, it is difficult to extract this colorless, transparent, dilute gas.

Systems that capture dew or fog and collect the extracted liquid in containers have long existed. But in dry areas where there isn’t much dew, special materials such as temperature-sensitive hydrogels, metal-organic frameworks (MOFs), or zeolites (crystalline aluminosilicates) can help extract small amounts of moisture from the air and release the water when heated. However, for these materials to be practical on a large scale, they must be incorporated into compact, portable devices, including their heat source.

To achieve the latter, Xiangyu Li’s team at the Massachusetts Institute of Technology (MIT) in the United States has developed a moisture harvester that could meet these requirements.

It is a compact device with fins covered with a material that first traps moisture and then generates drinking water when subjected to heat.

The researchers designed these water-adsorbing fins by placing a copper foil between copper foams coated with a commercially available zeolite.

Compared to previous studies where the focus was on materials development, the authors of the new study found that combining the adsorption support with the material properties resulted in thin and compact adsorbent fins that can rapidly collect water.

As a proof of concept, they created a device with 10 tiny adsorbent fins placed one after the other on a copper base plate about 2 millimeters apart—a distance that optimizes moisture capture from desert-like air, which contains just 10 percent relative humidity. Within an hour, the fins became saturated and then released the trapped moisture when the base reached 184 degrees Celsius.

The new, simple and compact system first collects moisture from the air (left) and then releases it (right) when heated, resulting in drinkable water. (Image: Xiangyu Li)

With 24 collection and release cycles, the team estimates that 1 liter of absorbent coating on the fins could produce up to 1.3 liters of drinking water per day in air with 30% relative humidity, a volume two to five times greater than that obtained with previously developed devices.

According to the creators of the new device, with further development it could be integrated into existing infrastructure that produces waste heat, such as buildings or transport vehicles, in order to provide a cost-effective option for generating drinking water in arid regions.

Xiangyu Li and colleagues present the technical details of their new device for extracting water from the air in the academic journal ACS Energy Letters, under the title “Design of a Compact Multicyclic High-Performance Atmospheric Water Harvester for Arid Environments.” (Source: American Chemical Society)