Recent progress in black phosphorus nanosheets for improving the fire safety of polymer nanocomposites

The application of black phosphorus (BP) nanosheets to improving the fire safety of polymers has been intensively explored in recent years. The phosphorus-rich construction, inherent layered structure, and ease of surface modification contribute to the highly efficient flame-retardant performance of BP nanosheets. Reported results confirmed that BP nanosheets and BP-based hybrids could reduce the release of heat, suppress fire spreading, and reduce the emission of smoke and toxic gases during the combustion of polymers. However, the poor air and moisture stability, severe synthesis conditions, and difficulty to scale up limit their wide application. Up to date, there is no review about BP-based flame retardants for improving the fire safety of polymer nanocomposites. In this review, we summarize the proposed, preparation approaches, surface modification methods and improved air stability, and flame-retardant mechanisms of BP nanosheets and flame-retardant BP nanosheets/polymer composites. The fire safety of polymer nanocomposites is discussed to specifically illustrate the functions of BP nanosheets. Lastly, the limitations and the outlook of using BP nanosheets as flame retardants are presented.