(339b) Insight into Selective Binding of Carbon Dioxide on Carbon Quantum Dots through Molecular Dynamics and Monte Carlo Simulations at the Atomic Level

To effectively tackle the challenges posed by global climate change, a practical approach involves capturing CO₂ directly at its source; thus, utilizing an abundant, sustainable, and cost-effective adsorbent with high selectivity is crucial. This study leverages established synthesis methods to create adsorbents from Kraft softwood lignin (KSL), a biobased material that meets these criteria and is recyclable, while also enabling the recovery of adsorbed gases. KSL, a coproduct produced in large quantities at pulp and paper mills worldwide, serves as the foundation for this research.

Enhancing the internal surface of the adsorbents using carbon quantum dots (CQDs), which were derived from lignin themselves, was found to be an effective method to increase adsorption capacity and selectivity of CO₂ over other gas molecules. CQDs facilitate the selective adsorption of CO₂ gas molecules driven by electrostatic interactions, taking advantage of the unique quadrupole moments exhibited by CO₂, N₂, and O₂. This manipulation of charge distribution on CQDs can be achieved through methods such as nitrogen or oxygen doping during synthesis, or by introducing amine, carboxyl, or hydroxyl groups within the aromatic structure or at the edges.

To evaluate the binding strength, adsorption isotherms and selectivity of CQDs towards CO₂, N₂, and O₂, a combination of classical molecular dynamics simulations and Grand Canonical Monte Carlo simulations were employed across various carbon substrate materials at different temperatures. Statistical analysis of CQD-gas interactions was used to quantify adsorption selectivity and capacity. The results demonstrate the potential to modify binding strength and selectivity for CO₂ over N₂, and O₂ by controlling the charge distribution of CQDs on a carbon substrate. Ongoing efforts are focused on optimizing the atomic structure and dimensions of CQDs, as well as the extent of doping and functionalization, to achieve a viable large-scale adsorbent solution for CO₂ capture.