Effective CO₂ adsorption at low pressure over nitrogen-enriched porous carbons, derived from melamine-loaded polyaniline

Polyaniline (PANI)-derived carbon has been applied in various adsorptions because of the presence of nitrogen and relatively high porosity. In this study, melamine/PANI mixture was pyrolyzed at low temperatures (500–650 °C) to derive porous carbons with high nitrogen content because of added melamine. Obtained carbons (Melamine/PANI-derived Carbons, MPCs) were characterized and applied in CO₂ adsorption under low pressure, and MPC-550 (prepared at 550 °C) showed much better performance than PC-550, derived from pure PANI, because of high N content (since N leads to polarity and basicity, which are helpful for CO₂ adsorption) and narrow pores (even with low porosity). For example, MPC-550 and PC-550 (prepared at 550 °C) had adsorption capacity of 1.2 and 1.0 mmol/g (at 0.15 atm); and isosteric heat of adsorption (IHA) at zero coverage of 46 and 32 kJ/mol, respectively. On the other hand, N₂ adsorption relied mainly on porosity; therefore, MPC-550 had lower N₂ adsorption than PC-550. Accordingly, MPC-550 and PC-550 showed ideal adsorbed solution theory selectivity (CO₂/N₂) of 75 and 61, respectively, under 1 atm. MPC-550 had competitive selectivity compared with other carbon-based adsorbents. MPC-500, prepared at 500 °C, showed very high selectivity (1 1 0) and IHA (48 kJ/mol); however, had relatively low CO₂ adsorption because of low porosity. Based on the advantages of MPC-550, compared with those of PC-550, adding nitrogenous compounds (like melamine) to PANI, before pyrolysis, is one of the recommendable methods for porous carbons, especially with high N content. Finally, MPC-550 was recyclable in CO₂ adsorption and can be suggested as a promising adsorbent for CO₂ capture from offgas.