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

Area of Science:

• Materials Science
• Environmental Chemistry
• Chemical Engineering

Background:

• Nitrogen doping enhances activated carbon (AC) performance for gas adsorption.
• Limited research exists on simultaneous N and O functional group evolution in ACs, especially from oxygen-rich precursors.
• Coal-derived ACs offer a promising platform for functionalization.

Purpose of the Study:

• To synthesize nitrogen-doped activated carbons (NACs) from coal using K2CO3-assisted activation and melamine co-pyrolysis.
• To investigate the impact of doping temperature on N and O functional groups and their influence on CO2, H2O, and toluene adsorption.
• To establish a rational design strategy for multicomponent gas adsorption in ACs for flue gas treatment.

Main Methods:

• Physical activation of coal using K2CO3 to produce high-surface-area ACs.
• Nitrogen doping via co-pyrolysis with melamine at temperatures ranging from 600-900 °C.
• Characterization of surface area, pore volume, and surface functional groups (N and O).
• Gas adsorption experiments for CO2, H2O, and toluene.

Main Results:

• Synthesized ACs exhibited high surface areas (up to 940 m²/g) and micropore volumes (0.36 cm³/g).
• Nitrogen content ranged from 1.44 to 7.68 at%, and oxygen content from 6.89 to 10.39 at% based on doping temperature.
• A balance of N and O functionalities, including pyrrolic nitrogen, ether, and hydroxyl groups, enhanced CO2 and H2O adsorption (NAC-600).
• Higher doping temperatures (NAC-900) favored toluene adsorption due to increased graphitization and graphitic N/ether groups.

Conclusions:

• The distribution of N and O functional groups, rather than just porosity, is critical for selective gas adsorption.
• Optimized surface chemistry in NAC-600 significantly improved CO2 and H2O uptake.
• NAC-900 demonstrated superior toluene adsorption capacity, highlighting the role of graphitic structures.
• This study provides a pathway for designing advanced ACs for complex flue gas compositions.