Efficiency of carbon dioxide capture with metal substitutions in the MIL-88A metal-organic framework.

Carbon dioxide capture is a vital approach for mitigating air pollution and global warming. In this context, metal-organic frameworks are promising candidates. Particularly, MIL-88A (M), where the metal nodes (M) are connected to fumarate linkers in its structure, has demonstrated significant potential for CO2 capture. However, to date, no studies have investigated the effects of metal substitutions in MIL-88A (M) on CO2 capture performance. Therefore, the present work aims to address this gap by examining metal substitutions with M = Al, Sc, Ti, V, and Ga. To quantitatively understand the CO2 capture capabilities of MIL-88A (M), we employed grand canonical Monte Carlo simulations to study both excess and total CO2 uptakes. Our findings indicated that MIL-88A with Al and Ga as metal nodes exhibited the best performance for CO2 capture. Furthermore, the adsorption energy of the CO2 molecule in MIL-88A (M), obtained through van der Waals-corrected density functional theory calculations, indicated the following order of preference for CO2 adsorption: Ti > V > Sc > Ga ≈ Al. The adsorption strength of the CO2 molecule in MIL-88A (Ga and Al) was the weakest among the considered metals. However, MIL-88A (Al) exhibited the largest specific surface area and hence offered the best excess and total gravimetric uptakes, while MIL-88A (Ga), together with MIL-88A (Al), had the largest pore volumes. Therefore, they exhibited the best excess and total volumetric uptakes. The electronic density of states revealed that the interaction between the 3σ g , 2π u , and 1π g peaks of the CO2 molecule and the O and C p x and p y orbitals of MIL-88A (M) was found to be significant for understanding the physical interaction between CO2 and MIL-88A (M). Thus, our findings provide valuable insights for the rational design of metal-organic frameworks for gas capture and storage applications.