Potassium salt-assisted synthesis of highly microporous carbon spheres for CO2 adsorption

Highly microporous carbon spheres for CO2 adsorption were prepared by using a slightly modified one-pot Stöber synthesis in the presence of potassium oxalate. Formaldehyde and resorcinol were used as carbon precursors, ammonia as a catalyst, and potassium oxalate as an activating agent. The resulting potassium salt-containing phenolic resin spheres were simultaneously carbonized and activated at 800 °C in flowing nitrogen. Carbonization of the aforementioned polymeric spheres was accompanied by their activation, which resulted in almost five-time higher specific surface area and total pore volume, and almost four-time higher micropore volume as compared to analogous properties of the carbon sample prepared without the salt. The proposed synthesis resulted in microporous carbon spheres having the surface area of 2130 m2 g−1, total pore volume of 1.10 cm3 g−1, and the micropore volume of 0.78 cm3 g−1, and led to the substantial enlargement of microporosity in these spheres, especially in relation to fine micropores (pores below 1 nm), which enhance CO2 adsorption. These carbon spheres showed three-time higher volume of fine micropores, which resulted in the CO2 adsorption of 6.6 mmol g−1 at 0 °C and 1 atm.