Preparation of N-doped activated carbons with high CO2 capture performance from microalgae (Chlorococcum sp.)

Abstract

N-Doped activated carbons with high CO₂ adsorption capacity have been prepared from sugar-rich microalgae (Chlorococcum sp.) feedstock via simple hydrothermal carbonization coupled with KOH activation or NH₃ modification. The KOH activated carbons exhibit higher CO₂ capture performance compared with the ones treated by NH₃. The nitrogen-enriched hydro-char derived from microalgae was activated with KOH at 700 °C to improve the textural characteristics (surface area, pores size, and total pore volume), and the resulting carbon showed a highly ordered structure with a surface area of 1745 m² g⁻¹, and narrow pore size distribution with the maxima peak located in the micropore range (<1.0 nm). The activated carbon exhibited CO₂ uptakes of 4.03 and 6.68 mmol g⁻¹ at 25 °C and 0 °C, respectively. Further XPS analysis revealed the effective pyridonic-nitrogen species (up to 58.32%) on the carbon surface favored a higher CO₂ capture capacity. The N-doped activated carbons displayed rapid adsorption kinetics with ultrahigh selectivity for CO₂ over N₂ (up to 11 at 25 °C), and no obvious decrease in the CO₂ uptake capacity was observed even after seven cycles, which may be due to the dominant physisorption between CO₂ and the surface of carbon.