CO2 adsorption performance of nitrogen-doped porous carbon derived from licorice residue by hydrothermal treatment

For high-value and environmentally friendly utilization of industrial herbal waste, a series of licorice residue-derived porous carbons were prepared with nitrogen-doped hydrothermal carbonization and KOH activation. The N-doped porous carbon activated at 600 °C exhibited excellent CO2 adsorption capacity (6.43 mmol/g at 0 °C and 1 bar, 3.89 mmol/g at 25 °C and 1 bar), high CO2/N2 selectivity (21.3), and high initial isosteric adsorption heat (28.7 kJ/mol). The excellent CO2 adsorption of the sorbent can be ascribed to its high microporosity and nitrogen content. At 0 °C and 1 bar, the ultramicropore volume below 0.7 nm contributes almost equally with the N content. However, the N content plays a dominative role at higher temperature or lower pressure. N content, especially N-5 content, performs a sound correlation with the CO2 adsorption capacity under ambient condition.