Silicon-Doped Carbon Nanotubes: Promising CO<sub>2</sub>/N<sub>2</sub> Selective Agents for Sequestering Carbon Dioxide

2016-10-10T00:00:00Z (GMT) by Misaela Francisco-Marquez Annia Galano
The potential ability of single-walled silicon–carbon nanotubes (SWSiCNTs) as CO<sub>2</sub> 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 CO<sub>2</sub> 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 CO<sub>2</sub>, 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 CO<sub>2</sub> over N<sub>2</sub>, which is a critical feature for materials with potential applications for CO<sub>2</sub> capture. The rate constants for the SWSiCNT reactions with CO<sub>2</sub> were found to be around 10<sup>5</sup> M<sup>–1</sup> s<sup>–1</sup>, which suggests that they are fast enough to ensure efficient CO<sub>2</sub> capture at room temperature. In addition, for the SWSiCNT with 33% Si, the possibility of multiple CO<sub>2</sub> adsorption was also investigated (up to seven CO<sub>2</sub> molecules). It was found that all the consecutive reactions are significantly exergonic, which indicates that one SWSiCNT is able to sequester several CO<sub>2</sub> equivalents. These findings suggest that SWSiCNT-based materials are promising candidates for selectively, and efficiently, sequestering CO<sub>2</sub> molecules, in particular, SWSiCNTs with intermediate (2–33%) Si amounts.