A group of researchers based in the US has created a new metal–organic framework (MOF) capable of selectively adsorbing two molecules of carbon monoxide at each metal site. This innovative breakthrough signifies a considerable advancement in the design of MOFs, potentially allowing for more efficient capture of other gases than previously possible.
MOFs, renowned for their ability to engage specific molecules, were recognized in this year’s Nobel Prize in Chemistry, emphasizing their role in storage and filtration applications. Typically, each site in a MOF can only adsorb a single target molecule. However, there have been rare occurrences of ‘co-operative adsorption’, where the uptake of one molecule aids in the uptake of additional molecules.
The remarkable accomplishment by the team, which includes Kurtis Carsch from the University of Texas at Austin and is spearheaded by Jeffrey Long from the University of California, Berkeley, involved the creation of CoMe-MFU-4l, a MOF that incorporates cobalt(II)–methyl sites. At room temperature and a partial pressure of merely 10 millibars, this framework adsorbed significantly higher amounts of carbon monoxide than traditional MOFs, while requiring much greater pressures for adsorbing other gases. Importantly, the adsorption was reversible under vacuum conditions, and the material maintained 98% efficiency even after 50 cycles.
Their investigation reveals that the adsorption of an initial carbon monoxide molecule triggers a spin transition in the cobalt ion, thereby allowing a second molecule to fit between the cobalt and the methyl group, a mechanism that operates independently of other bonding sites within the MOF.
The research group is examining possible applications, such as hydrogen purification, where the material could avert irreversible poisoning of fuel cells by carbon dioxide. Chemical engineer Andrew Medford from the Georgia Institute of Technology expressed interest in the reversibility of the covalent bond formation mechanism, highlighting the potential for previously overlooked exotic binding modes in computational studies.
This research highlights the bright prospects of MOFs in gas capture and purification technologies, encouraging further exploration into optimizing spin-state interactions for improved performance.