Water stress affects about half of the world’s population. Given the presence of clean water in the atmosphere, porous and hygroscopic sorbents are being investigated for water extraction from the air.
Now, the University of Chicago researchers found a way to extract even more water.
In 2021, the Pritzker School of Molecular Engineering’s Laura Gagliardi designed materials for a device that can extract water out of the air, even in dry climates like deserts. The material called a metal-organic framework (MOF) is a hybrid structure of metal ions and organic linkers that can be tuned at the molecular level. The MOFs have an empty pore structure that adsorbs water molecules from the air, similar to a sponge.
The team has now helped guide the design of an optimized MOF that adsorbs 50% more water from the air compared to the state-of-the-art water-harvesting material MOF. Though the original MOF worked well, the team wanted to improve it by increasing the material‘s pore volume while keeping a similar binding strength to water.
The MOF framework consists of tiny aluminum-based rods connected by linker molecules. This structure generates pores that are lined by alternating hydrophilic (water-binding) and hydrophobic (water-avoiding) pockets. These pockets are ideally suited for binding initial water molecules – when the MOF is exposed to air, water molecules naturally bind themselves to it. Once the initial water molecules are bound, the following molecules attach themselves to the initial water molecules.
However, the researchers wanted to increase the pore volume while still keeping this special environment needed to attract the initial water molecules. They also had to find the right sweet spot in design – water needed to bind to the MOF, but not too strongly, or else it could never be desorbed (squeezed out of the sponge).
With the help of computer simulations, researchers ultimately found the answer – adding in a special linker extension, essentially a long arm on the structure made from two carbon atoms, that would increase the pore size while retaining the special water-binding properties the MOF originally had.
The team is now scaling up the production of this new MOF and incorporating it into their prototype water-collecting device. If it works as well in the device as in the lab, it could collect significantly more water than before.
Next, they are working on making more changes to the design and integrating machine learning that can sift through the data they’ve gained through their modeling and experiments to give new suggestions for improvement. Ultimately, the device could be used to help soldiers in combat in arid areas or civilians in water-scare regions.
- Nikita Hanikel, Daria Kurandina, Saumil Chheda, Zhiling Zheng, Zichao Rong, S. Ephraim Neumann, Joachim Sauer, J. Ilja Siepmann, Laura Gagliardi, and Omar M. Yaghi. MOF Linker Extension Strategy for Enhanced Atmospheric Water Harvesting. ACS Central Science, 2023; DOI: 10.1021/acscentsci.3c00018