Robust nitrogen-doped microporous hollow carbon spheres for energy-efficient CO2 capture from flue gas

Nitrogen (N)-doped microporous hollow carbon spheres were prepared by facilely nanocasting spherical SiO 2 with N-containing melamine phenolic resin through a simple in-situ polymerization process. Through regulating the dosage of melamine, N content in microporous hollow carbons could be easily tuned to an unprecedented level of 49.2 wt%. Additionally, in order to address the common problem of relatively poor structural porosity of N-doped carbons, especially after incorporating vast N into carbon frameworks in reported literature, a comprehensive strategy including optimizing carbonization temperature and performing further activation by CO 2 and KOH were explored, and their effects on material textural properties and CO 2 capacity were systematically studied. Although this strategy did not completely avoid the N loss during activation of carbon materials, it sharply promoted the textural properties of carbon materials at the expenses of partial N and efficiently produced a series of highly microporous carbon materials, still with abundant N species (11.5 ∼ 29.9 wt%) and large structural porosity (330 ∼ 1263 m 2 /g). More importantly, these N-doped microporous hollow carbons, when used for CO 2 capture, showed superior CO 2 capacities of 3.00 mmol/g (25 °C and 1 bar) and 1.05 mmol/g (40 °C and 0.1 bar), exceptionally robust cyclic stability, and low regeneration energy of 2.75 GJ/ton CO 2 , which is much lower than aqueous amine-based absorbents and comparable to amine-supported adsorbents. Thus, these outstanding adsorption performances make the N-doped microporous hollow carbon spheres prepared in this study more promising for energy-effective CO 2 capture from dilute gas streams.