Effect of host framework on the diffusion process in microporous material: a molecular dynamics simulation investigation

One of the central assumptions when a particle moves through a window in microporous materials is that interaction of the diffusing particle with the silicon (Si) and aluminum (Al) atoms of the framework can be neglected, as the presence of bulkier oxygen in the host structure is thought to hinder close proximity of the diffusing particle to Si and Al. We examine this assumption, exploring the diffusion path and cross-checking the bottleneck associated with the diffusion process. Our study reveals that short-range interactions between the diffusing species and Si/Al of the host have a significant effect on the diffusion process. Guest-host interaction energy increases significantly if interaction between Si and Al atoms with the diffusing species is considered. The self-diffusion coefficient (D) decreases significantly in the linear regime, whereas in the anomalous regime, surprisingly, D increases. The increase in D is due to a decrease in the activation energy in the anomalous regime, whereas in the linear regime, activation energy increases, thus D decreases.