Single-step thermal treatment of single-walled carbon nanotubes for enhanced CO2 adsorption capacity

Abstract We report a single-step thermal treatment method to significantly increase the specific surface area (SSA) of single-walled carbon nanotubes (SWCNTs), improving their performance in CO 2 adsorption. An ambient heat treatment of SWCNTs at 400 °C for 4 h increased the BET SSA from 448 to 858 m 2 /g; this enhancement results from the oxidation of catalyst residues and the opening of SWCNT caps, thereby exposing the inner channels. Further purification by HCl reflux removed residual catalysts but enhanced nanotube bundling, resulting in a decreased value of SSA (736 m 2 /g). A water reflux control experiment confirmed that the SSA decreases stems from bundling rather than acid treatment. In dynamic (breakthrough) CO 2 adsorption tests, the thermally treated SWCNTs reached an uptake of 5.0 mmol/g, and purified samples reached 4.5 mmol/g, both significantly higher than the pristine SWCNTs (2.7 mmol/g), representing 85% and 67% improvements, respectively. By comparing experimental surface areas and CO 2 uptakes, we estimated the adsorption cross-section of CO 2 to be around 27 Å 2 , which agrees with the literature. Monte-Carlo and geometric simulations supported these findings, indicating that CO 2 adsorption predominantly occurs on the accessible surfaces of SWCNTs rather than uniformly across the entire surface area within nanotube bundles. This study illustrates that a simple thermal treatment can effectively enhance SWCNTs for CO 2 capture, providing a practical and scalable strategy for improving nanocarbon-based adsorbents. Graphical Abstract