Density functional studies of protonated and alkali metal (Li, Na and K) incorporated T-doped 2D zeolite model (T = B, Ga)

Abstract

Ab initio calculations based on density functional theory (DFT) have been performed to investigate the role of trivalent atoms substituting silicon atom in the 2D zeolite model. The effects of the B and Ga atoms on the stability, structural and electronic properties of the 2D zeolite model are explored. Our DFT calculations reveal that the introduction of B atom is exothermic whereas that one of Ga atom is endothermic. The structural analysis shows that the incorporation of B and Ga atoms affects the bond lengths of the system, however it does not lead to a significant deformation of the structure. The Fermi level of the doped systems is shifted towards the valence band, indicating that the incorporation of these trivalent atoms leads to p_ type materials. The second purpose of this study is to find the suitable charge compensations among hydrogen and alkali metals as well as their site preference (either on the surface or in the cages of the silica bilayer). The calculated formation energy values are similar, suggesting both configurations could co-exist. Hydrogen has the lowest formation energy and the proton affinity analysis predicts low acid strength of H-B- compared to H-Ga-doped 2D zeolite, a similar trend to that of bulk zeolite. Among the alkali elements, we found that Na and K atoms are the most stable ones. The density of states analysis shows that the Fermi level is lying within the gap, and defect states are observed near the band edges narrowing the band gap of the system. This work provides detailed and valuable information about the atomic-level properties of the relatively recent 2D zeolite model, which is beneficial for its industrial applications.