Researchers from UC Berkeley and several other universities have uncovered more in depth the process by which certain three-dimensional crystals function.
The team, led by campus chemistry professor Omar Yaghi and Korea Advanced Institute of Science and Technology researcher Osamu Terasaki, conducted a study published Monday that focused on the adsorption process of metal-organic frameworks, or MOFs.
MOFs are porous three-dimensional crystals with large surface areas. They typically have a metal oxide center that is surrounded by organic molecules and were invented by Yaghi in the early 1990s. MOFs have the potential to be used to create high-octane fuels for cars and to capture certain air pollutants, among other applications.
“One gram of these little MOFs can have a larger surface area than a football field,” said UC Berkeley chemistry professor Jeffrey Long. “(This characteristic of MOFs) is important for applications such as gas storage and gas separations.”
While there have been many studies on the interactions between gases and surface area within a pore, this new study focused on the interpore relationships within MOFs.
Their findings show that MOFs follow a very specific adsorption process.
According to Terasaki, the pores first adsorb the gases, then at a certain thickness, the MOF reaches capillary condensation, a condition in which high pressure condenses the gas to become liquid. The MOF forms a superlattice, a periodic structure of pores. The filled pores finally interact with the neighboring pores to form a uniform lattice expansion.
“Up to now, everybody believed gas adsorption was random,” Terasaki said.
The team used instruments created by Terasaki and his colleagues specifically for this study. These instruments were used to perform small-angle X-ray scattering, which shoots an X-ray beam at the MOF in very specific atmospheric conditions and measures the changes in direction of the beam that bounces off the MOF to infer its atomic structure.
“You can put together a picture of its various properties, not just its composition, (with these instruments),” said campus chemistry professor Gabor Somorjai.
According to a press release, Yaghi said this study can help scientists figure out what makes one MOF better than another in certain situations.
Long pointed out that the ability of MOFs to carry out gas separations has the potential to help the environment. According to Long, MOFs can remove carbon dioxide from factory emissions and change it into its pure form to be used for scientific purposes or even stored underground and be turned into its mineral form.
The prospect of MOFs being used commercially, however, is still far off.
“It takes a long time before newly discovered materials are manufactured on a large scale,” Long said.