Dual optimization of microporosity in carbon spheres for CO2 adsorption by using pyrrole as the carbon precursor and potassium salt as the activator

Abstract

Nitrogen-doped microporous carbon spheres (CSs) were prepared via the Stöber method by simultaneous carbonization and activation of nitrogen-doped polymer spheres obtained in the presence of potassium citrate. Both additional microporosity and nitrogen doping in CSs were achieved by using pyrrole as one of the carbon precursors. A very high CO₂ uptake of 7.35 mmol g⁻¹ at 0 °C and 1 bar pressure was achieved for the carbon sample, which possessed the highest ultramicropore volume of 0.42 cm³ g⁻¹ among all samples studied. Potassium citrate was shown to be an efficient in situ activator, which generated a high volume of ultramicropores below 0.8 nm at a temperature as low as 700 °C, while the use of polypyrrole led to an additional ultramicroporosity in CSs. Microporosity was simply tuned in CSs by varying the potassium salt content in the synthesis mixture. The resulting CSs possessed narrow pore size distributions with a large fraction of micropores below 1 nm and exhibited high CO₂ uptakes ranging from 3.30 mmol g⁻¹ to 7.35 mmol g⁻¹ at 0 °C and 1 bar pressure, indicating the potential applicability of these carbons not only as CO₂ sorbents but also in other applications such as energy storage in supercapacitors.