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Dr. David Jenkins


Jenkins_2The two teams’ microcrystal designs are called Covalent Organic Frameworks (COFs). While, robust bonds hold these nanostructures together under the harshest conditions, no COFs have as yet been created with a special affinity for CO2. This is the target Custelcean and Jenkins have set for themselves.

Assembled from building blocks of repeating nodes held together by linking units, carefully planned construction could make COFs capable of trapping molecules, such as carbon dioxide, in their pores. When flue gas is forced through the microcrystals under pressure, the CO2 would stick to inner-pore compounds designed to attract these molecules more strongly than other elements in the gas—which push on through. Releasing the pressure frees the CO2 from the pores.

In year oneJenkins_3 Jenkins’ team synthesized first-generation tetrazole linking units; Custelcean’s LDRD team is using these to assemble COFs designed to attract carbon dioxide based on their electronic structure. Research on porous polymer films suggests nitrogen-based tetrazoles (five-member rings with four nitrogen atoms) and triazoles (similar but with three nitrogen atoms) improve the film’s ability to capture carbon dioxide. Custelcean’s team branched out from their originally proposed three-dimensional design to two-dimensional COFs that layer like sheets of graphite. The new configuration allows for shorter linking units, which simplifies preparation.

Jenkins’ year two research continues preparation of linking units for both designs. His team will share these with Custelcean’s team and use them to synthesize 2- and 3-D COFs with nodes prepared by the LDRD team.


JDRD project:
Triazole and tetrazole linkers for covalent organic frameworks for carbon dioxide capture
David Jenkins, UT Chemistry Department

LDRD project:
Novel covalent organic frameworks with tailored carbon capture functionality

Radu Custelcean, ORNL Chemical Sciences Division


Lab EquipmentAkin to Metal Organic Frameworks (MOFs) discovered twenty years ago, COFs hit the new materials scene just ten years ago. Both materials have three-dimensional, porous nanostructures built from repeating nodes held together by linking units. With carefully planned construction, each has the potential to trap molecules, such as carbon dioxide or hydrogen, and hold them in the pores for later release. MOFs have metal-ion nodes and organic linkers; COFs are assembled solely from organic building blocks and address a problem MOFs encounter in CO2 capture from flue gas.

“Most MOFs react with water, particularly the acidic water found in flue gas,” Jenkins says, “The metal-ligand bonds are weaker, making it harder for them to hold up in high heat [and] humid and acidic conditions.”

COFs have robust covalent bonds held together by shared electrons, so they are less likely to fall apart under similar conditions. On the down side, Jenkins says, COFs with a special selective affinity for CO2 have as yet to be created.

CloudsThis is the task Jenkins and Custelcean have laid out for their teams. Custelcean will synthesize frameworks and linkers designed to attract carbon dioxide based on their electronic structure. Jenkins’ linkers feature nitrogen-based compounds called tetrazoles (five-member rings with four nitrogen atoms) and triazoles (similar but with three nitrogen atoms). Recent research with porous polymer films suggests tetrazole and triazole compounds improve CO2 selectivity and uptake.

But, synthesizing COFs is not for the faint of heart. “We do combinatorial chemistry,” Jenkins says.

“It’s very much a black-box approach, in that you set up hundreds of reactions on a very small scale, making tiny changes to each, and then observe what you get. If something looks promising, we do it again on a larger scale, testing and scaling-up until we have enough material to do a full gamut of tests.

“If we can functionalize these really small pores that have no metal in them—that are much more stable once they are synthesized—and actually show they interact and bind the CO2 more strongly than with other gases, I would consider that a huge success.”


JDRD project:
Triazole and Tetrazole Linkers for Covalent Organic Frameworks for Carbon Dioxide Capture
David Jenkins, UT Department of Chemistry

LDRD project:
Novel Covalent Organic Frameworks with Tailored Carbon Capture Functionality
Radu Custelcean, ORNL Chemical Sciences Division