Metal Organic Framework Based Adsorbents for CO2 Capture

Abstract

The rapid increase in CO2 emissions has necessitated the development of new, effective strategies for carbon capture and storage. As shown in literature studies, Metal-Organic Framework (MOF) – based adsorbents have emerged as promising candidates due to their tunable functionalities and exceptional adsorption properties. This thesis presents an investigation on designing MOFs for the purpose of CO2 capture.

In this work, four novel Yttrium-based MOFs were successfully synthesized using pyrimidine-4,6dicarboxylic acid – based ligands and characterized. The objective of this study is to synthesize Y-based MOFs with the functional groups -H (unfunctionalized), -OH, -Cl, and -NH2 implemented on the pyrimidine ligand, then investigate the effects of these groups on CO2 adsorption capacity. The synthesized MOFs were labelled as Y-MOF-1 (amino-functionalized), Y-MOF-2 (hydroxy-functionalized), Y-MOF-3 (unfunctionalized), and Y-MOF-4 (hydroxy-functionalized). Y-MOF-3 and Y-MOF-4 were found to be composed of stacked 2-dimensional layers with solvent molecules occupying the interlayer space. Y-MOF-3 possessed hexagonal-shaped layers, resulting in a honeycomb (hcb) topology. As for Y-MOF-4, the stacked layers possessed rhomboidal shapes. As for Y-MOF-1 and Y-MOF-2, structural analysis revealed the presence of channels. Y-MOF-1 was found to possess a Gismondine (gis) topology, while Y-MOF-2 displayed a NbO topology. Scanning-electron microscopy (SEM) images revealed that Y-MOF-1 has no consistent morphology; however, the majority of the particles display a rod-shaped morphology. These two MOFs (Y-MOF-1 and YMOF-2) were selected for CO2 and N2 adsorption studies. The experimental results revealed that YMOF-1 and Y-MOF-2 have Brunauer, Emmett and Teller (BET) surface areas of 5.32 and 4.28 m2/g, respectively and CO2 uptake values of 0.219 and 0.082 mmol/g at 25oC and 1 bar, respectively.

Additionally, an isostructural series of three copper-based MOFs was synthesized using the same tetrazole-based ligand with different functional groups (-COOCH2CH3, -COOH, and -H (unfunctionalized)). These MOFs were labelled as Cu-tet-e (functionalized with -COOCH2CH3), Cu-tet-c (functionalized with -COOH), and Cu-tet (unfunctionalized). Based on structural analysis, these frameworks are composed of stacked layers with hexagonal-shaped channels, which are pillared by ligand molecules. This results in a Kagome (kag) tiling 3-dimensional topology. SEM images revealed that these novel materials possess hexagonal-rod shaped crystals. CO2 and N2 adsorption studies were also conducted for the copper-based MOFs. The determined CO2 uptake values are 0.676, 0.353, and 0.148 mmol/g at 25oC for Cu-tet-e, Cu-tet-c, and Cu-tet, respectively.

Date of Award	Aug 2023
Original language	American English
Supervisor	Mohamed Infas Haja Mohideen (Supervisor)