Carbon Dioxide\nCapture on Oxygen- and Nitrogen-Containing\nCarbon Quantum Dots

To address global climate change challenges, an effective\nstrategy\ninvolves capturing CO<sub>2</sub> directly at its source using a sustainable,\nlow-cost adsorbent. Carbon quantum dots (CQDs), derived from lignin,\nare employed to modify the internal surface of an activated carbon\nadsorbent, enabling selective adsorption based on electrostatic interactions.\nBy manipulating charge distribution on CQDs through either doping\n(nitrogen) or functionalization (amine, carboxyl, or hydroxyl groups),\nthe study confirms, through classical molecular dynamics simulations,\nthe potential to adjust binding strength, adsorption capacity, and\nselectivity for CO<sub>2</sub> over N<sub>2</sub> and O<sub>2</sub>. For simulations with a single component gas, maximum selectivities\nof 3.6 and 6.7 are shown for CO<sub>2</sub>/N<sub>2</sub> and CO<sub>2</sub>/O<sub>2</sub>, respectively, at 300 K. Simulations containing\na wet flue gas indicate that the presence of water increases the CO<sub>2</sub>/N<sub>2</sub> and CO<sub>2</sub>/O<sub>2</sub> selectivities.\nThe highest CO<sub>2</sub>/H<sub>2</sub>O selectivity obtained from\na CQD/graphite system is 4.3. A comparison of graphite and lignin-based\ncarbon composite (LBCC) substrates demonstrated that LBCC has enhanced\nadsorptive capacity. The roughness of the LBCC substrate prevents\nthe diffusion of the CQD on the surface. This computational study\ntakes another step toward identifying optimal CQD atomic architecture,\ndimensions, doping, and functionalization for a large-scale CQD/AC\nadsorbent solution for CO<sub>2</sub> capture.