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Metal–organic frameworks (MOFs) are a revolutionary new class of crystalline solids that can be designed to trap myriad kinds of matter, including greenhouse gases, or to be used as nanosized drug carriers. They can also pull water from desert air.

A chief characteristic of MOFs, which some have been called “miracle materials,” is how much empty space they comprise. Often described in the scientific literature as “ultra highly porous,” the sponge-like nano-structures have the greatest internal surface area of any known material. Unfolded and spread flat, a single gram of MOF could cover a football field.

MOFs, as well as other novel chemical structures, including covalent organic frameworks (COFs) and zeolitic imidazolate frameworks (ZIFs), have sprung from a field called reticular chemistry—a name coined by its pioneer, Berkeley chemist Omar Yaghi, who has appointments at both Cal and the Lawrence Berkeley Lab.

Professor Omar Yaghi (photo by Marcus Hanschen, UC Berkeley)

Professor Yaghi and his Berkeley team made headlines recently for creating an MOF that can harvest water from extremely dry air. The MOFs trap water molecules overnight and release them the next morning as water vapor, which is then condensed as the drinkable stuff. Each pound of MOF powder collects about 1.3 liters of water every 12 hours. Better still, the system can operate on solar energy alone and the MOFs are reusable. The process can repeat night after night.

According to Yaghi, the technology is also eminently scalable. “You can use a kilogram [of MOF] or a hundred kilograms if you have a village to water. You can use a thousand kilograms! That would be sitting out there … harvesting water.”