Atomic-scale insights into laser-induced patterned graphitization of combustion-derived soot

Soot has long been recognized as a representative combustion by-product and a major contributor to environmental pollution. Direct utilization of soot as a functional carbon material is fundamentally limited by its high defect density and intrinsically disordered carbon structure. Consequently, most previous studies focused on suppressing soot formation, whereas studies of potential evolution of the intrinsic structure of soot remain limited. We combine ReaxFF molecular dynamics (MD) simulations with experimental characterization to elucidate the formation mechanism of candle soot and its graphitization behavior induced by laser-driven thermal reconstruction at the atomic scale. Laser-induced graphitized candle soot was observed to form a carbon nano-onion (CNO)-like multilayered graphitic structure with an interlayer spacing of ∼0.35 nm, and Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy confirmed the pronounced reduction in defect density along with enhanced sp² carbon ordering. In the MD simulations, the quantitative structural evolution of laser-induced graphitized candle soot (LIGCS) was investigated by analyzing atomic-scale chemical pathways, carbon ring evolution, gas emission yields, the R defect ratio, sp 1 fraction, and the orientational order parameter (S). Notably, at 2700 K, the defect ring ratio decreases to ∼0.66 while maintaining a surface area of 495.48 Ų, indicating that this temperature represents the optimal condition within the graphitization soft-annealing process window. Overall, this study demonstrates that laser-induced thermal reconstruction enables formation of CNO-like graphitized architectures from soot, revealing a new pathway for upcycling soot into functional carbon materials.