Sub-Ångström-level engineering of ultramicroporous carbons for enhanced sulfur hexafluoride capture

Ultramicroporous carbon materials are realized by exploiting nitrogen-doping and alkali ions activation strategies on classical carboxylic phenolic resins. Through tuning the nitrogen-doped content as well as activation strength and size of the alkali ions, carbon materials present pore sizes that are controlled at the sub-Ångström level from 5.8 to 7.7 Å with precision between 0.1 and 0.4 Å. The fine-tuning of the ultramicropore size using melamine as the sacrificial templating agent improves the practicality of the carbon materials for the recovery of SF₆ which are larger than conventional molecules such as CO₂. Resultantly, the optimized carbon material at 1 bar and 25 °C saw a >16-fold increase in SF₆ adsorption from 0.39 to 6.55 mmol g⁻¹ while the SF₆/N₂ selectivity reached as high as 78.8. We attribute this to the fine-tuning of ultramicropores, leading to optimizable pore sizes that allow easy access to the large surface areas of carbon materials by the SF₆ molecules. Furthermore, owing to its high adsorption performance, a 1.5-fold higher breakthrough SF₆ adsorption capacity alongside a 2-fold increase in SF₆/N₂ selectivity were realized under dynamic breakthrough conditions. The stability and recyclability of the carbon materials were also demonstrated with a long-term performance evaluation of up to 10 consecutive adsorption-desorption cycles.