Spontaneous formation of nitrogen – doped hierarchical porous microcrystalline nanosheets with improved CO2 capture at low and medium pressures

Abstract

Bio-based porous carbon is considered as a promising adsorption material due to its good CO2 capture performance and ideal CO2/N2 selectivity. In this study, a series of nitrogen-doped hierarchical porous microcrystalline carbon nanosheets (PMCNs) were obtained by adjusting the Fe/Zn metal ratio using microalgae as carbon precursors and applied to CO2 capture at low and medium pressure. The results show that the SBET and Vtotal of PMCN-2 are as high as 1764 m2·g−1 and 1.89 m3·g−1, respectively, and their corresponding CO2 adsorption capacities are 4.73 mmol g−1 at low pressure (1 bar, 273.15 K) and 18.54 mmol g−1 at medium pressure (8 bar, 273.15 K). The effects of pore size and nitrogen functional groups were analyzed by theoretical calculation. Grand canonical Monte Carlo (GCMC) confirms that slit micropores (0.7–1.5 nm) are key factors for low-pressure CO2 adsorption, while narrow mesopores (2–5 nm) are beneficial structures for medium-pressure CO2 capture. In addition, nitrogen doping changes the charge distribution on the surface of the carbon sheet and promotes the interaction with CO2, in which pyridine nitrogen and graphite nitrogen effectively enhance the medium-pressure adsorption and selectivity.