Density Functional Theory (DFT) Study on the Adsorption Mechanism of Carbon Dioxide on Nitrogen-Doped Graphene Surfaces

Carbon dioxide (CO₂) capture and utilization are critical strategies to mitigate global warming and manage industrial emissions. In this work, we employ spin-polarized Density Functional Theory (DFT) calculations with dispersion corrections (DFT-D3) to systematically investigate the adsorption mechanism of CO₂ on various nitrogen-doped graphene (N-graphene) surfaces, including graphitic (quaternary), pyridinic, and pyrrolic nitrogen configurations. Our computational results reveal that pristine graphene exhibits very weak physisorption toward CO₂ with an adsorption energy of only -0.12 eV. Conversely, the introduction of nitrogen dopants significantly enhances the local chemical reactivity of the carbon scaffold. Among the studied configurations, pyridinic N-graphene displays the strongest affinity for CO₂ with an adsorption energy of -0.48 eV, accompanied by a noticeable charge transfer of 0.18 e from the substrate to the CO₂ molecule, which induces a slight bending of the linear CO₂ geometry (O-C-O angle of 172.4°). Electronic structure analyses, including Density of States (DOS) and charge density difference plots, confirm that the enhanced adsorption is driven by the hybridization of the nitrogen lone pairs and the adjacent carbon p_z orbitals with the unoccupied π* orbitals of the CO₂ molecule. These findings provide fundamental thermodynamic and electronic insights into the design of cost-effective, metal-free carbon-based materials for efficient carbon capture and separation technologies.