CO2 Capture by Cyclodextrin MOFs is Hindered by Their Hydrophilicity

The rising levels of carbon dioxide (CO2) in the atmosphere pose a significant environmental concern due to their contribution to global warming and climate change. Post-combustion carbon capture (PCCC) and storage is one method to minimize CO2 emissions. Cyclodextrin-based metal-organic frameworks (CD-MOFs) are potential adsorbents for PCCC because of their high CO2 sorption capacity. Here, we used Grand Canonical Monte Carlo (GCMC) simulations to investigate the adsorption of CO2 on various CD-MOFs. Results showed that CD-MOFs are selective for water and CO2 molecules over nitrogen and oxygen molecules. The Rb-CD-MOF had the highest CO2 uptake, while K-CD-MOF exhibited the highest isosteric heat of adsorption. However, all CD-MOFs had much higher water sorption capacity than CO2, and Cs-CD-MOF had the highest water uptake. Moreover, our results showed that CD-MOFs had lower CO2 adsorption capacity when combined with other gases than under pure gas conditions. We also discovered that hypothetical transition metal – based CD-MOFs behave similarly with alkaline metal – based CD-MOFs during combined gas sorption studies, suggesting that enhancing the ligand-coordination bond may have only a minimal effect in the hydrophobicity of the CD-MOFs. Other strategies for endowing hydrophobicity to CD-MOFs must be sought if it were to be deployed as an adsorbent for post-combustion carbon capture. Overall, this study underscores the importance of considering other gases in the performance assessment of MOFs for CO2 capture.