Distribution and Transport of CO<sub>2</sub> in Hyperbranched Poly(ethylenimine)-Loaded MCM-41: A Molecular Dynamics Simulation Approach
Junhe Chen, Hyun June Moon, Kyung Il Kim, Ji Il Choi, Pavithra Narayanan, Miles A. Sakwa‐Novak, Christopher W. Jones, Seung Soon Jang
Abstract
High Resolution Image Download MS PowerPoint Slide Fossil fuel use is accelerating climate change, driving the need for efficient CO 2 capture technologies. Solid adsorption-based direct air capture (DAC) of CO 2 has emerged as a promising mode for CO 2 removal from the atmosphere due to its potential for scalability. Sorbents based on porous supports incorporating oligomeric amines in their pore spaces are widely studied. In this study, we investigate the intermolecular interactions and adsorption of CO 2 and H 2 O molecules in hyperbranched poly(ethylenimine) (HB-PEI) functionalized MCM-41 systems to understand the distribution and transport of CO 2 and H 2 O molecules. Density Functional Theory (DFT) is employed to compute the binding energies of CO 2 and H 2 O molecules with HB-PEI and MCM-41 and to develop force field parameters for molecular dynamics (MD) simulations. The MD simulations are performed to examine the distribution and transport of CO 2 and H 2 O molecules as a function of the HB-PEI content. The study finds that an HB-PEI content of approximately 34 wt % is thermodynamically favorable, with an upper limit of HB-PEI loading between 45 and 50 wt %. The distribution of CO 2 and H 2 O molecules is primarily determined by their adsorptive binding energies, for which H 2 O molecules dominate the occupation of binding sites due to their strong affinity with silanol groups on MCM-41 and amine groups of HB-PEI. The HB-PEI content has a considerable impact on the diffusion of CO 2 and H 2 O molecules. Furthermore, a larger number of water molecules (higher relative humidity) reduces the correlation of CO 2 with the MCM-41 pore surface while enhancing the correlation of CO 2 with the amine groups of the HB-PEI. Overall, the presence of H 2 O molecules increases the CO 2 correlation with the amine groups and also the CO 2 transport within HB-PEI-loaded MCM-41, meaning that the presence of H 2 O enhances the CO 2 capture in the HB-PEI-loaded MCM-41. These findings are consistent with experimental observations of the impact of increasing humidity on CO 2 capture while providing new, molecular-level explanations for the macroscopic experimental findings.