A team of chemists at the University of Iowa has developed a light-activated crystal structure that can pull water from the air and store it inside nanoscale cavities, offering a new approach to atmospheric water harvesting.

The material is built from metal-organic frameworks, or MOFs, which are porous structures formed by linking metal atoms with organic molecules. In this case, researchers designed a lattice that initially had no usable cavities for water storage.

The breakthrough came when the structure was exposed to ultraviolet light. The light triggered a chemical rearrangement inside the crystal, reshaping its internal architecture and creating tiny cavities capable of trapping water molecules from the air.

Researchers say the process turns the material into a kind of solid-state water harvester that works using only sunlight, without the need for external power sources or complex machinery.

The team observed the effect at the microscopic level using X-ray diffraction, which revealed that water molecules were already present inside the newly formed cavities after the light exposure.

Light opens water traps

“We have found and validated a way to capture and to store water that would require only sunlight,” says Leonard MacGillivray, adjunct professor in the Department of Chemistry and former department chair.

“You can transport the crystal lattice and eventually release the water on demand. That’s why it’s such an advance.”

Researchers say the material’s behavior depends on a structural shift triggered by UV light. The organic linkers inside the MOF rearrange into a new configuration, opening up spaces that act as storage sites for water molecules.

The system can store about 5 percent of its weight in water under laboratory conditions. While that amount is small at the single-crystal level, researchers believe scaling up the architecture could significantly increase overall water capture potential.

Sun-powered water capture

The team believes the concept could help develop new water-harvesting technologies for regions facing severe water scarcity.

“The reason why we use the word ‘intelligent’ is because we’re triggering the water capture intentionally with the light,” says graduate researcher Nevindee Samararathne Muhandiramge.

“UV light is freely available from the sun. So, the next step would be to determine the limits of the water uptake in terms of mass percent and push that limit as far as we can.”

The researchers also note that the crystals assemble themselves, allowing for potentially large-scale production of the material in the future.

However, they caution that the current version is still a proof of concept. The material uses cadmium as a test element, which would need to be replaced with safer alternatives before real-world deployment.

Researchers say future work will focus on improving water uptake efficiency and testing whether the system can operate reliably outside controlled laboratory conditions.

The study suggests a new direction for water-harvesting materials that combine structural chemistry with environmental responsiveness, using sunlight as the only energy input.

The study, “Photo capture of water by single crystals of a nonporous metal−organic material,” was published in Journal of the American Chemical Society.