SCIENCE

You can’t squeeze blood from a stone, but wringing water from the desert sky is now possible, thanks to a new spongelike device that uses sunlight to suck water molecules from air, even in low humidity. (Science)

How else is solar energy being harnessed?

Teachers, scroll down for a quick list of key resources in our Teachers Toolkit.

Discussion Ideas

• The great Science article describes a new prototype device that uses solar energy to pull water out of thin air. Where does the water seemingly created by the device actually come from?
  • It really does come from the air, although air is not really all that thin. The air that surrounds our planet is thick with gases such as nitrogen, oxygen, argon, carbon dioxide, helium, neon … and water. (Read our encyclopedic entry to learn more about our amazing atmosphere.)
    • Atmospheric water is probably most obvious to us in humid weather, in which the air contains a large amount of water. However, smaller amounts of atmospheric water are present even in arid climates.

• The new device relies on MOFs to extract water molecules from the air. What are MOFs? Read the Science article for some help, or cue the video to about 14 seconds.
  • MOF stands for metal organic framework. MOF “networks assemble in a Tinkertoy-like fashion from metal atoms that act as the hubs and sticklike organic compounds (ligands) that link the hubs together. By choosing different metals and organic ligands, chemists can dial in the properties of each MOF, controlling what gases bind to them, and how strongly they hold on.”
    • The metal used in the water harvesting MOF is zirconium. The powdered MOF is pressed into a thin sheet of copper metal and placed between a solar absorber and a condenser plate.
  • Research into MOFs is widespread, and includes analyzing their possible use in:
    • hydrogen storage. Hydrogen storage is crucial to developing more efficient vehicles using fuel-cell technology.
    • complex chemical reactions. MOFs have potential as heterogeneous catalysts, which can exist in a different phase than reactants. Heterogeneous catalysts have been described as “science for a sustainable future,” contributing to more efficient renewable fuels, fuel cells, and renewable chemicals.
    • drug delivery. Because scientists can control the chemical properties of MOFs, they may able to safely and efficiently deliver medications to different tissues or organs.
    • methane storage. Science describes these MOFs as “a type of high-capacity gas tank for natural gas–powered vehicles.”
    • semiconductors. Under the right conditions, some MOFs behave as semiconductors, and a film of these MOFs could contribute to more efficient and reliable photovoltaic technology.
    • carbon capture. In particular, MOFs could act as a more efficient type of carbon “scrubber” for some coal-fired power plants.

• How does the water-harvesting device work? Take a look at the great Science diagram for some help.
  • At night, the device is opened, allowing air to flow into a MOF that grabs and holds water molecules.
  • During the day, the chamber is closed, and the sun’s heat causes the MOF to release the water as vapor that condenses and is collected. The device, using one kilogram of MOF, is able to extract 2.8 liters (3 quarts) of water a day from air with humidity as low as 20%.

• What obstacles remain for the water harvester?
  • It’s a complex device that can’t be easily assembled by people not working at MIT and Berkeley.
  • The zirconium used in the MOF “costs $150 a kilogram (2.2 pounds), making water-harvesting devices too expensive to be broadly useful.”

• Why is this water harvester considered such an important development?
  • The device has the potential to help address the freshwater crisis, in which millions of people do not have access to clean freshwater. Learn more about the freshwater crisis with our lesson plan.
  • The device is especially intriguing because it holds potential for use in arid and remote areas that are not connected to a power grid or water pipeline system.
    • The chemist in the video, Omar Yaghi, reminds us that “One-third of the world’s population lives in arid regions, where water is scarce. But the air in those regions contains about 30% humidity.”

TEACHERS TOOLKIT

Science: This new solar-powered device can pull water straight from the desert air

UC Berkeley: Pulling drinkable water out of dry air

Nat Geo: What is solar energy? encyclopedic entry

Nat Geo: Will there be enough freshwater? lesson