Mechanistic insights into N,P-codoped carbon dots for enhancing flame retardancy of wood: From nanoscale design to macroscopic performance

Chinese fir is one of the important wood resources in China, with strong market demand and economic value. However, its flammability is a drawback that cannot be ignored. To enhance the fire safety performance and value-added utilization value of thinning Chinese fir in China, this study employed a one-step hydrothermal method to convert the material into nitrogen and phosphorus co-doped carbon dots (N,P-CDs), enabling nanoscale modulation of material properties and systematically investigating their influence on the flame-resistant properties of wood. The results revealed that: (1) the synthesized N,P-CDs exhibited uniformly dispersed spherical structures with an average particle size of 8.653 nm and displayed typical optical properties of carbon dots; (2) as a novel flame retardant, N,P-CDs enhanced the limiting oxygen index (LOI) of the treated wood to 37.35% and achieved a V-1 classification in the UL-94 vertical burn test, achieved by a cooperative flame inhibition mechanism acting in both gaseous and solid phases.; (3) cone calorimetry data exhibited an approximate 50% reduction in the heat release rate (HRR) and a 41% decrease in the total smoke production (TSP). The findings establish a viable pathway for creating high-value utilization of thinning wood, while also provides theoretical support and technical foundation for the application of biomass-based functional materials in wood flame retardancy. • Sustainable Flame Retardancy: N,P-CDs flame retardants with a size of less than 10 nanometers were prepared by a one-step method, which have good dispersibility and permeability. • Transform forestry waste into high-value-added functional nanomaterials to enhance the fire safety performance of Chinese fir. • N,P co-doping synergistic flame retardancy：The flame retardant properties of Chinese fir are enhanced through synergistic effects between gas phase and condensed phase.