摘要：Black phosphorus (BP) nanosheets are commonly used flame retardants in polymers, but the challenge of poor dispersion in the polymer matrix makes their addition relatively large, which undoubtedly increases the cost of BP-based flame-retardant materials due to the expensive price of BP. Here, progressive approximation is adopted as a macroscopic methodological guidance for BP dispersion, where the dispersions and aggregates in partially dispersed solutions are continuously separated by multiple experiments to finally approach a uniform dispersion state. Additionally, a bio-based interfacial layer is also constructed on the BP surface (i.e., BNTP) to reduce black phosphorus self-aggregation and further promote dispersion as well as achieve synergistic flame retardancy through microscopic interfacial engineering. The rationality of this method is verified by BNTP modified epoxy thermosets, which achieve a UL-94 V0 level and a LOI of 29.4% with an ultralow BNTP loading (0.3 wt%). This work provides a facile concept for achieving uniform dispersion of 2D nanosheets in organic matrices from a mathematical methodological guidance, and simultaneously contributes to a significant reduction in the BP content in polymer matrices, solving the cost problem of BP-based flame-retardant materials and promoting their industrialization.