Engineering Accessible Adsorption Sites in MOFs for CO2 Capture
- Clark Atlanta Univ., Atlanta, GA (United States)
The overall goal of this project was to synthesize metal-organic frameworks (MOFs) with improved CO2 adsorption and selectivity properties for potential application in removing this greenhouse gas from flue gas streams during fossil fuel processing. MOFs are an important class of 2-dimensional (2D) and 3D supramolecular coordination polymer networks that are comprised of organic linkers (ligands) and metal ion-units or clusters. They generally possess very high surface area, porosity, variable thermal stability and tunable chemistry, which make them potential candidates for CO2 adsorption. The three specific objectives of this project were as follows: 1) To synthesize MOFs with metal ion adsorption sites in more accessible locations within the structures (towards the center of the organic linkers) in order to enhance their CO2 adsorption characteristics; 2) To investigate the CO2 adsorption properties of new MOFs containing pyrazine- and other nitrogen containing ligands as possible improved alternatives to known amine-functionalized MOFs; and 3) To investigate the nature of the adsorption sites and mechanism(s) by conducting computational studies on CO2 adsorption within the MOF structures and compare the results with experimental observations. The main outcomes of this research are as follows: Nitrogen-containing ligands that possess a diaza-12-crown-4-ether moiety at the center of two phenylcarboxylic acid groups were utilized to synthesize 3D MOFs in which the added transition metal ions (i.e. Co2+ and Mn2+) were coordinated within the crown moieties. Therefore, the structures had the metal ions in more accessible locations. The new 3D structures, being non-porous however, showed negligible adsorption capacity for CO2. The ligand 2,3,5,6,-pyrazinetetracarboxylic acid (PZTC) was successfully used to synthesize four new MOFs, each with one of the following metal ions; Ca2+(1D), Zn2+(2D), Mn2+ (3D) and Gd3+(3D), and with the dimensionality (D) indicated. The Ca-, Zn- and Mn- PZTC-based MOFs had no obvious accessible pores and showed no adsorption capacity for CO2. Gd-PZTC structure however, showed promising capacities of 1.0 mmol/g and 0.6 mmol/g at 273K and 298 K respectively. Another nitrogen-containing ligand explored was 2,2’-dinitro- trans-4,4’- stilbenedicarboxylic acid (DNSDC) and in combination with a co-ligand, 2,2’-bipyridine (2,2’-BPY). The combination of DNSDC with Co2+ and Mn2+ yielded four new thermally stable MOFs that showed significant CO2 absorption capacities. The experimental CO2 adsorption capacities varied among the structures, ranging between 1.8 mmol/g at 256 K and 0.8 mmol/g at 298K. The DNSDC-based structures maintained significant stability and capacities over many adsorption cycles at 298K. With 2,2’-diamino- trans-4,4’-stillbene dicarboxylic acid (DASDC) as ligand instead of DNSDC, new 3D MOF structures were also synthesized. The structures, however, were less stable, and decomposed on activation (exposure to vacuum and or solvents) and therefore showed negligible CO2 adsorption capacities. The dinitro-stilbene based MOFs showed promising CO2 adsorption capacities, thermal stabilities and recyclability, and therefore showed potential for application in CO2 removal from flue gas. The research accomplishments presented herein support the Department of Energy’s (DOE) Office of Fossil Energy and the National Energy Technology Laboratory (NETL) mission in the area of research that advances the science of coal technologies, specifically carbon capture and storage. The research outcomes can guide rational design/synthesis strategies towards producing advanced materials for CO2 capture. However, further research is needed in order to develop the materials to meet or exceed capacities and stabilities that are reported for their counterparts.
- Research Organization:
- Clark Atlanta Univ., Atlanta, GA (United States)
- Sponsoring Organization:
- USDOE Office of Fossil Energy (FE)
- DOE Contract Number:
- FE0022952
- OSTI ID:
- 1582449
- Report Number(s):
- DOE-CAU-22952
- Country of Publication:
- United States
- Language:
- English
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