A groundbreaking discovery in the world of metal-organic frameworks (MOFs) has been made by US researchers, who have developed a new MOF with an extraordinary ability to bind gases. This innovative MOF, named CoMe-MFU-4l, showcases a unique feature: it can selectively adsorb two molecules of carbon monoxide at each metal site, a phenomenon known as 'co-operative adsorption'.
MOFs have been a hot topic in chemistry, even earning the prestigious Nobel Prize this year, due to their remarkable molecular binding capabilities. Typically, each site in a MOF can only accommodate one target molecule, but this new MOF breaks that rule, and here's where it gets intriguing.
Kurtis Carsch, a synthetic inorganic chemist, explains that in some rare cases, the adsorption of one molecule can create a chemical reaction that makes it easier for subsequent molecules to bind. However, designing MOFs with this property for other gases has been a challenge.
The team led by Jeffrey Long at the University of California, Berkeley, has synthesized CoMe-MFU-4l, which contains cobalt(II)–methyl sites. At ambient temperature and low pressure, this MOF can adsorb an impressive 1.6 times more carbon monoxide than if each site held just one molecule. Moreover, it is highly selective, resisting the adsorption of other gases at higher pressures. The process is reversible, and the MOF retains its efficiency even after 50 cycles.
The researchers propose that the adsorption of the first carbon monoxide molecule triggers a spin transition in the cobalt ion, facilitating the binding of a second molecule. This process is unique as it doesn't require other bonding sites in the MOF.
Carsch hints at the potential for this discovery, suggesting that it could lead to the design of MOFs that can bind multiple oxygen atoms or acetylene molecules. The applications are vast, including hydrogen purification, as Carsch notes, "A lot of fuel cells using hydrogen can be poisoned by carbon dioxide, even at very low levels."
Andrew Medford, a chemical engineer from the Georgia Institute of Technology, is excited by this development. He is intrigued by the reversibility of a mechanism involving covalent bonds and believes it highlights the importance of considering spin in computational screening. Medford's perspective opens up a discussion on the potential for discovering more exotic binding modes in MOFs.
This discovery not only advances our understanding of MOFs but also has the potential to revolutionize gas capture and storage technologies. It's a fascinating development that challenges conventional wisdom and opens up new avenues for research and innovation.
