Engineering nitrogen and oxygen functionalities in naturally sourced activated carbon for multicomponent gas adsorption.

Nitrogen doping is a widely adopted strategy to enhance the gas adsorption performance of activated carbon (AC) adsorbents. However, the simultaneous evolution of oxygen and nitrogen functional groups-especially in carbon precursors with high oxygen content-has received limited attention. In this study, coal-derived ACs with high surface areas (up to 940 m2/g) and micropore volumes (0.36 cm3/g) were synthesized via K2CO3-assisted physical activation, followed by nitrogen doping through co-pyrolysis with melamine. By regulating the doping temperature (600-900 °C), the nitrogen content of the resulting samples ranged from 1.44 to 7.68 at%, while the oxygen content varied from 6.89 to 10.39 at%. After decoupling the influences of porosity, we found that a well-balanced distribution of N and O functionalities, especially pyrrolic nitrogen, ether (C-O-C), and hydroxyl (C-O-H) groups, was critical for enhancing CO2 and H2O adsorption. NAC-600 exhibited the most favorable surface chemistry for the adsorption of CO2 (15 vol%) and H2O (20% RH), achieving capacities of 41 mg/g and 59.9 mg/g, respectively. In contrast, NAC-900, prepared at the highest N-doping temperature, exhibited the best surface chemistry for toluene adsorption (550 mg/cm3), attributed to its higher degree of graphitization and the presence of graphitic N and ether groups. This work offers a rational design strategy for improving the multicomponent gas adsorption performance of activated carbons for flue gas treatment.