Researchers at the University of California, Berkeley, have managed to separate water from atmospheric air using little to no additional energy.

This was possible thanks to metal-organic frameworks, or MOFs, minuscule powders able to separate metals and organic compounds from each other. In the last 20 years, researchers have created over 20,000 different MOFs for a wide variety of applications, such as separating methane and water from other gasses.

metal-organic frameworks
The device can obtain up to 2.8 liters of water per cycle. Image credit: Evelyng Wang.

In 2014, lead researcher Omar Yaghi synthesized an MOF able to absorb water at the driest of natural conditions. He then resorted to Evelyn Wang, a mechanical engineer from MIT in Cambridge, who had worked with him on a previous project involving MOFs. The idea was to develop a “water harvesting device.”

New compounds for harvesting specific molecules

The system is meant to work overnight and during the day. At night, it would enter the adsorption stage, when the device is opened, and the air is let through the porous MOF, which takes hold of the water molecules. The MOF would be a one-kilogram sheet of dust-sized MOD crystals pressed on copper.

During the day, the chamber is closed and natural sunlight forces the MOF to release the water as vapor, which goes into a condenser and is collected in a separate chamber. Tests have shown that the system can condense at least 2.8 liters of water out of thin air per day if left running continuously.

Researchers behind the project have called it the realization of a “longstanding dream,” even if Yaghi himself suggests that there is a lot of potential for improving the concept. For example, the initial model uses zirconium, which is too expensive to be employed on a massive scale, but subsequent tests reveal that aluminum may work just as well. Furthermore, the system requires no additional input of energy.

Yaghi writes that atmospheric water comprehends at least 10 percent of all fresh water in lakes on Earth and that so far, there is no efficient process to capture and condense water from the air on different humidity settings.

“That’s really where the power of this chemistry comes into play. Where the composition of organic and inorganic and the balance between these two allows you to craft the interior so that it loves water, but it doesn’t hold onto it too tightly,” stated Yaghi according to The Washington Post.

The most effective way to turn air into water

The new device is no larger than a tissue box, and it manages to surpass in efficiency and effectiveness previous methods developed for extracting water from thin air. The most common methods are fog harvesting and dewing.

Fog harvesting requires the presence of fog, which is air at almost 100 percent humidity, while dewing uses water condensers to take water vapor from the atmospheric air, turning it into liquid. The problem with dewing is that it requires high amounts of power to maintain the condensers at an ideal temperature.

metal-organic frameworks
The system proposed by Yaghi uses sunlight without any additional power source, although water can only be collected throughout the day. If water is to be collected at night, then a heating system would have to be implemented. Image credit: Evelyng Wang.

Now, researchers are trying to bring the design to a practical level, where it can be implemented in industrial settings and even brought to underserved locations where water is scarce.

One of the radical advantages of the new MOF-based system is that it is designed for low humidity settings, as most water-collecting systems cannot harvest water from environments that have a 20 percent humidity level or lower.

MOFs have a wide range of potential uses besides separating water molecules from the air. They can also separate alcohols, sulfur, oxygen, odor-generating molecules, carbon dioxide, carbon monoxide, and much more. Researchers in the field propose that MOFs could be used for capturing carbon molecules in coal-powered plants in all of its stages. They could also be employed in delivering antitumoural and retroviral drugs to the body, specifically those that could help cure cancer and AIDS.

Yaghi was the first to develop MOFs, over 20 years ago. They can be carefully designed to pick up specific metals and organic compounds as they are holding onto more complex gasses.

On the other hand, earlier in January, a Chilean engineer had designed and tested a device called FreshWater, which can reportedly also extract water from thin air. FreshWater accelerates the natural water cycle by capturing moisture and forcing rain, obtaining up to 28 liters of purified water per day.

FreshWater consists of a larger tank with much higher energy requirements, able to produce from 9 to 28 liters of water per day with a 450W consumption rate. When put in perspective, using MOFs is immensely more efficient and cost-friendly compared to FreshWater, which requires an additional power source to function correctly.

Source: Science