Rapid microwave synthesis of nitrogen-doped ultramicroporous coal-based carbon with enhanced CO2 adsorption performance

Ningdong coal was used as the raw material to develop a synergistic 'pre-oxidation + microwave activation' strategy for the preparation of nitrogen/oxygen co-doped ultramicroporous coal-based activated carbons (ACs), for efficient CO2 adsorption. By tuning the microwave power and pretreatment conditions, the microcrystalline structure, pore size distribution, and surface functional groups of the ACs were precisely controlled. The results show that pre-oxidation significantly enhances nitrogen retention and doping efficiency, forming CO2-philic active sites dominated by pyridinic and pyrrolic nitrogen, with a maximum nitrogen content of 10.06 at.%. Meanwhile, a large number of ultramicropores (0.6–0.7 nm) were constructed, which effectively improved the CO2 adsorption capacity and selectivity. The optimized sample achieved CO2 uptake of 4.72 mmol·g−1 at 0 °C and 1 bar, and maintained 3.33 mmol·g−1 at 25 °C, with CO2/N2 selectivity greater than 50. This work provides theoretical guidance and a practical pathway for the structure–function co-regulation and carbon capture applications of low-cost coal-derived ACs.