Carbon Dioxide Capture on Oxygen- and Nitrogen-Containing Carbon Quantum Dots

To address global climate change challenges, an effective strategy involves capturing CO₂ directly at its source using a sustainable, low-cost adsorbent. Carbon quantum dots (CQDs), derived from lignin, are employed to modify the internal surface of an activated carbon adsorbent, enabling selective adsorption based on electrostatic interactions. By manipulating charge distribution on CQDs through either doping (nitrogen) or functionalization (amine, carboxyl, or hydroxyl groups), the study confirms, through classical molecular dynamics simulations, the potential to adjust binding strength, adsorption capacity, and selectivity for CO₂ over N₂ and O₂. For simulations with a single component gas, maximum selectivities of 3.6 and 6.7 are shown for CO₂/N₂ and CO₂/O₂, respectively, at 300 K. Simulations containing a wet flue gas indicate that the presence of water increases the CO₂/N₂ and CO₂/O₂ selectivities. The highest CO₂/H₂O selectivity obtained from a CQD/graphite system is 4.3. A comparison of graphite and lignin-based carbon composite (LBCC) substrates demonstrated that LBCC has enhanced adsorptive capacity. The roughness of the LBCC substrate prevents the diffusion of the CQD on the surface. This computational study takes another step toward identifying optimal CQD atomic architecture, dimensions, doping, and functionalization for a large-scale CQD/AC adsorbent solution for CO₂ capture.