Prof. Phillip Milner, chemistry and chemical biology, Kaitlyn Keasler grad and the Milner lab published an article on Sept. 29 on the utilization of metal-organic frameworks to capture and store fluorinated gases. Their novel methods can prevent these gasses from contributing to climate change and potentially produce pharmaceutical drugs and agrochemicals.
The Milner lab focuses on studying porous, sponge-like materials containing cavities for materials to interact with. They recently have been working with metal-organic frameworks, which are porous compounds with organic and metallic components, to study the compound’s potential applications in controlling organic reactions and synthesis.
The lab is particularly interested in how MOFs can be used to adjust reactions involving fluorine because it is a significant component in medications and agrochemicals. These reactions either use dangerous and unstable reagents or simpler reagents that are greenhouse gasses and difficult to work with.
“Protocols typically require multi step synthesis or the use of dangerous and highly unstable reagents,” Keasler said. “And many simple fluorinated building blocks are gasses, which are challenging to work with in the lab. And unlike solids and liquids, it is difficult to accurately measure the mass or volume of gaseous reagents.”
According to Kealser, MOFs have been found to be capable of reversibly storing fluorinated gasses within their pores. This is due to the Hard-Soft Acid-Base theory, which states that hard acids interact with hard bases and soft acids interact with soft bases. Because the MOF contains magnesium ions that act as hard acids, it interacts with fluorine, which are hard bases, transforming the gasses into crystallized solids and forming gas-MOF reagents.
These reagents allow for fluorination reactions to proceed much more rapidly with fewer steps compared to standard fluorination protocols. The use of MOFs in fluorination reactions also enable storage of gaseous fluorine compounds in various conditions, such as embedding them within wax capsules or on benchtop for up to two months.
Milner shared that by capturing fluorinated greenhouse gasses, such as sulfur hexafluoride, MOFs can also reduce the effects of climate change. Sulfur hexafluoride, a strong greenhouse gas that can stay in the atmosphere for thousands of years, is released from semiconductor industry emissions and has a global warming potential that is tens of thousands of times more potent than carbon dioxide.
Like sulfur hexafluoride, fluoroform has a global warming potential that is much more potent than carbon dioxide. The toxic and corrosive nature of both gasses allow for creation of medical and agricultural products upon capture by MOFs.
While the usage of MOFs has proven successful, it poses limitations such as excess waste.
“When the MOF has absorbed gas, it is about 30 percent gas and 70 percent other mass,” Milner said. “So you have a lot of extra solids and if you don’t reuse them, there’s a lot of waste there. That’s something we’d like to address by making frameworks that are cheap, lighter and can use even less to bind the gases.”
In addition to improving their capability, the Milner lab plans to expand the number of greenhouse gasses that the MOFs can bind to. They also hope to utilize captured fluorinated gasses to produce compounds that can selectively label proteins. Keasler said that the lab aims to make the application of MOFs to fluorinated gasses more generalizable and commercialized in order to grant other chemists easy access to these new methods.
“Fluorine is this really fascinating element that is in drug molecules and agrichemicals, but it’s also got this dark side,” Milner said. “That’s something we’re trying to now explore on both sides: how do we capture these destructive greenhouse gasses, and how do we develop new kinds of ways to install fluorine in more economical, cheap and user-friendly ways?”