Morphing metal-organic material harvests water from thin air

When it’s exposed to ultraviolet (UV) light, a new metal-organic material (MOM) can reversibly capture water from air (J. Am. Chem. Soc. 2026, DOI: 10.1021/jacs.6c01019). The water molecules slot into cavities formed in the MOM when it reacts with light. Although this material is only a proof of concept, it could work with just sunlight to help harvest water in low-humidity environments.

MOMs are made of metals and linkers, but unlike metal-organic frameworks (MOFs), they don’t necessarily contain mazes of pores for capturing molecules. “MOM is a broad term for compounds containing metal ions and organic linkers, whereas MOFs are a specific subset,” says Aisha N. Bismillah, a supramolecular chemist at King’s College London and the Francis Crick Institute who was not involved with the new work. In other words, MOMs represent the umbrella category of fruits, and MOFs represent bananas, she says.

The new MOM is a crystalline network of cadmium-metal centers connected by linkers that contain carbon-carbon double bonds. The material starts as a closed structure and “only creates the necessary space for water storage upon ultraviolet light stimulation,” says lead author Leonard R. MacGillivray of the University of Sherbrooke. This transformation reshapes the MOM’s crystalline structure and expands the empty space inside the material by approximately 3%—enough to enclose and entrap water.

The UV light drives a cross-linking cycloaddition between the double bonds that sit near each other in the MOM’s structure, explains Grace Han, who studies photochemistry at the University of California, Santa Barbara, and wasn’t involved in the study. Although the underlying crystalline cubic structure of the MOM is preserved, the reaction creates cavities that can capture water, she says.

When you want to get the water back out, you can just heat the material. The release happens easily because the water is held only by intermolecular interactions—hydrogen bonds and van der Waals forces, Han says. “While water uptake is not competitive with MOFs, the value [of this discovery] is conceptual, . . . a genuinely fresh contribution to supramolecular chemistry.”

The study presents “a unique combination” of MOMs and molecules ready to react to light stimuli, Bismillah says. It is the first time photochemical reactions in the materials have created cavities to soak up water; the cavities’ special shape and their bonding accommodate the water molecules just right, she adds.

Cadmium could become a handicap if this material is scaled up because it is “highly toxic” and linked to “major health issues and environmental effects,” Bismillah notes. Han says a path toward safer solutions could be swapping out the metal centers for “zinc, zirconium, or titanium analogs with an acceptable toxicity profile.” The authors say that stability and durability tests are essential, and they “are definitely exploring the integration of other metals and applications of the water capture,” MacGillivray says.

Although the MOM is far from capturing the same volume of water as MOFs, it is “interesting” to use “ultraviolet radiation to trigger a reaction resulting in a rigidified structure to adsorb water,” University of California, Berkeley, MOF pioneer and 2025 chemistry Nobel laureate Omar M. Yaghi says in an email to C&EN. The new research presents an unusual way to turn a nonporous structure into a porous one, but scientists must still measure how much water the material can adsorb, he says.

MacGillivray agrees. “We still need to perform benchmark studies to make direct comparisons,” he says. Nevertheless, he expects the MOM to become a competitor in capturing water, especially “in low-humidity capture and retention.” Moreover, the reactivity with UV light could create a “passive, sustainable solution” in which simple sunlight could activate the capture of water from air, MacGillivray adds. “We [want] to explore scale-up opportunities towards practical, real-world applications.”