Potassium citrate-assisted eco-friendly synthesis of tannin-derived nitrogen-doped micro–mesoporous carbon microspheres

Nitrogen-doped micro–mesoporous carbon microspheres (N-MMCSs) were successfully synthesized using condensed tannins in place of synthetic phenolic compounds as carbon precursors. Such N-MMCSs were fabricated using a modified one-pot Stober method in the presence of Pluronic F127 and potassium citrate which act as a structure-directing agent and an alternative activating agent, respectively. In addition to using tannins instead of synthetic phenolic resin precursors, lysine was employed as both a base catalyst and nitrogen source in lieu of toxic ammonia, further demonstrating a green synthesis. The development of porosity in N-MMCSs was achieved by varying the amount of potassium citrate added to the reaction. The resulting polymer spheres with incorporated potassium salts and nitrogen species were simultaneously carbonized and activated at 800 °C. This strategy affords activated N-MMCSs having high specific surface area, micropore volume, and mesopore volume up to 971 m2/g, 0.38 cm3/g, and 0.27 cm3/g, respectively with the retention of spherical morphology, mesoporous structure, and the presence of nitrogen species that results in high CO2 uptakes at ambient temperatures. This work opens a new avenue in the synthesis of carbon spheres with tunable porosity to meet the specific requirement of given applications.