Mechanistic insights into the role of alkali metal activation in CO2 adsorption by nitrogen-doped coal-based carbon materials

Abstract

Nitrogen-doped coal-based carbon materials have attracted significant attention in the field of CO₂ capture due to their low cost, high specific surface area, and tunable surface chemistry. However, the mechanism by which alkali metal activation (e.g., K/Na) influences CO₂ adsorption performance remains unclear, particularly regarding the synergistic effects between alkali metals and nitrogen species, as well as their impact on the electronic structure. In this study, density functional theory (DFT) was employed to systematically investigate the synergistic mechanisms between alkali metal activation (K, Na) and typical nitrogen doping configurations—pyridinic-N, pyrrolic-N, graphitic-N, and amine-N—on CO₂ adsorption performance in coal-based carbon materials. By constructing and optimizing C–O–M (M = K, Na) structures co-doped with nitrogen, we calculated the CO₂ adsorption energies and analyzed the corresponding electronic characteristics. The results show that the formation of C–O–M structures significantly enhances CO₂ adsorption capacity: Na-doped (−35.88 kJ mol⁻¹) and K-doped (−31.72 kJ mol⁻¹) systems exhibit much higher adsorption strengths than nitrogen-only doped counterparts (−17 to −13 kJ mol⁻¹). Further analysis of weak interactions revealed that alkali metals generate regions of high electrostatic potential on the carbon surface (at K/Na sites), while pyridinic-N introduces low-potential zones, thereby forming a strong electrostatic gradient field. This study uncovers the electronic role of alkali metals beyond their traditional function as pore-forming agents and highlights the dominant contribution of electrostatic interactions in CO₂ adsorption. These findings provide theoretical guidance for the synergistic optimization of pore structure and surface chemistry, promoting the rational design of high-performance coal-based CO₂ adsorbents.