Enhanced gas adsorption performance of bilayer Ti₃C₂ MXenes by Na intercalation: a first-principles study

Gas adsorption technology plays a vital role in environmental remediation, energy storage, and industrial separation. Two-dimensional (2D) MXenes, particularly Ti₃C₂, have attracted increasing interest due to their tunable interlayer spacing and rich surface chemistry. In this study, first-principles calculations were used to investigate the gas adsorption behavior of bilayer Ti₃C₂ and the enhancement mechanisms introduced by Na intercalation. The results show that pristine Ti₃C₂ exhibits weak physisorption for NH₃ and CO₂, whereas Na intercalation significantly improves adsorption strength for NH₃, CO₂, H₂, and O₂ by modifying the electronic structure and increasing charge transfer. Differential charge density maps and Bader charge analysis reveal that Na atoms donate electrons to the Ti₃C₂ surface, enhancing polarization and electronic coupling with gas molecules. Notably, Na intercalation enables dissociative adsorption of O₂ and increases H₂ adsorption stability. This study uncovers the atomic-level mechanisms by which Na atoms enhance gas adsorption and offers theoretical guidance for the design of high-performance MXene-based materials for gas separation, sensing, and storage.