Influence of the defect of activated carbon surface on cigarette smoke components adsorption: A DFT study

As a porous carbon adsorption material, activated carbon (AC) was used widely with the characteristics of large specific surface area, adjustable pore structure and surface chemical properties. This work focuses on elucidating the defect-mediated adsorption mechanisms of smoke-specific high-toxic components (nicotine, a major toxic alkaloid; phenol, a typical carcinogenic aromatic) together with CO and N₂O on activated carbon. It addresses the critical research gap of scarce systematic DFT studies on the atomic-scale adsorption of nicotine and phenol on defective carbon, with an emphasis on deciphering intrinsic electronic mechanisms underlying defect-enhanced adsorption. The study revealed that defective carbon surfaces exhibited significantly higher adsorption capacities than the pristine counterparts, as evidenced by lower adsorption energies for all target molecules. Notably, while defect-enhanced adsorption on carbonaceous materials is well-documented, systematic DFT investigations on nicotine and phenol - two smoke-specific high-toxicity organics - remain scarce. Specifically, defect-induced electron redistribution promoted charge transfer and orbital hybridization, critical for the chemisorption of toxicants. These findings establish a predictive structure-activity relationship between defect electronic properties and adsorption selectivity/capacity, providing targeted guidance for engineering high-efficiency adsorbents to reduce harmful components in cigarette smoke.

All calculations were performed using the Gaussian 16 software package. Structural optimizations and frequency analyses of calculation configurations were performed at the B3LYP/def2svp level, while single-point energy calculations utilized the B3LYP/def2tzvp basis set. To elucidate the underlying mechanisms, wave function analyses, Mayer bond order (MBO), electrostatic potential (ESP), Frontier molecular orbital (HOMO-LUMO), Hirshfeld atomic charges, and Charge Density Difference (CDD) were conducted. These investigations demonstrated that surface defects enhance local electronegativity and chemical reactivity at adsorption sites, facilitating stronger interactions with polar constituents of cigarette smoke.