Silicon-Doped Carbon Nanotubes: Promising CO₂/N₂ Selective Agents for Sequestering Carbon Dioxide

The potential ability of single-walled silicon–carbon nanotubes (SWSiCNTs) as CO₂ scavengers was investigated using density functional theory calculations and (5,5) SWSiCNT models with 2%, 33%, and 50% Si. It was found that while the reactions between CO₂ and pristine C tubes are endergonic, Si-doped materials have exergonic adsorption routes. It was also found that 50–50 Si–C composition is not required for the SWSiCNTs to be able to sequester CO₂, which seems to be relevant because this is the maximum Si–C proportion allowed to maintain the SWSiCNT stability. The modeled SWSiCNTs are predicted to be selective to CO₂ over N₂, which is a critical feature for materials with potential applications for CO₂ capture. The rate constants for the SWSiCNT reactions with CO₂ were found to be around 10⁵ M^–1 s^–1, which suggests that they are fast enough to ensure efficient CO₂ capture at room temperature. In addition, for the SWSiCNT with 33% Si, the possibility of multiple CO₂ adsorption was also investigated (up to seven CO₂ molecules). It was found that all the consecutive reactions are significantly exergonic, which indicates that one SWSiCNT is able to sequester several CO₂ equivalents. These findings suggest that SWSiCNT-based materials are promising candidates for selectively, and efficiently, sequestering CO₂ molecules, in particular, SWSiCNTs with intermediate (2–33%) Si amounts.