Facile synthesis of nitrogen-rich porous carbon spheres assisted by NaNH2 as a bifunctional activator and nitrogen source for CO2 capture

Abstract

It is more important for CO2 adsorbents to simultaneously contain large micropore volume and abundant nitrogen species. In the current work, we proposed a facile approach to synthesis millimeter-sized N-doped porous carbon spheres with developed micropores assisted by NaNH2 as a bifunctional activator and nitrogen source under a mild conditions. The obtained porous carbon spheres show the BET surface areas of 592–2513 m2/g and total N contents of 0.28–5.87 wt% respectively. Abundant micropore volume (pore size < 1 nm) and nitrogen species are mainly created at activation temperature less than 550 °C. The O species formed by preoxidation play an important role in the incorporation of N-containing functional groups that enable the enhancement of CO2 adsorption. The optimal sample of ACSO-Na-550 can achieve high CO2 uptake of 5.83 mmol/g at 0 °C and 1 bar. Furthermore, the ACSO-Na-550 exhibits large CO2/N2 selectivity, excellent recyclability, fast CO2 adsorption rate and high dynamic CO2 uptake due to the synergetic effect of its abundant micropore volume (pore size < 1 nm) and nitrogen species. In addition, the NaNH2 activation possesses the outstanding superiority compared with steam and KOH activation under relatively moderate conditions, endowing porous carbon spheres with promising application for CO2 capture.