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

Abstract

Nitrogen (N)-doped microporous hollow carbon spheres were prepared by facilely nanocasting spherical SiO2 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 CO2 and KOH were explored, and their effects on material textural properties and CO2 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 m2/g). More importantly, these N-doped microporous hollow carbons, when used for CO2 capture, showed superior CO2 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 CO2, 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 CO2 capture from dilute gas streams.