Photothermal and fire-safe epoxy/black phosphorene composites: Molecular structure analysis of sutured char

• 1. Photothermal of EP/SL-EBP-CoP is linearly increased (r 2 >0.994). • 2. EP/SL-EBP-CoP 2 separately reduces PHRR, THR and PCOP by 59.88%, 39.26% and 36.41%. • 3. Phosphorus, P-O-P and P-O-C are nodes, units and capture bonds in 3D sutured char. • 4. Rupture molecules of char layer (C n H 2n+2 PO 4 , m/z=168, 139 and 124) are discovered. To overcome the high flammability of polymers and endow them with photothermal capability, we fabricate the targeted nanofiller black phosphorus (BP) based SL-EBP-CoP for epoxy. Interestingly, the good ability of photothermal for EP/SL-EBP-CoP 2.0 nanocomposite changes with irradiation power can be linearly quantified (r 2 >0.94). Secondly, EP/SL-EBP-CoP 2.0 separately reduces peak heat release rate (HRR), total HRR and peak carbon monoxide (CO) production by 59.88%, 39.26% and 36.41% compared with EP, along with the lowest fire growth index. The significantly reduced hazard of heat and CO is attributed to the combined effects of 2D BP, catalysis of CoP and the structure of sutured char. Finally, the pyrolysis of BP-based flame retardants produces P 4 , P 3 and P 2 with an abundance of 77.10%, 6.75% and 14.70%. Moreover, flame retardant composites are highly dependent on the final char. This work demonstrates that phosphorus and P-O-P (PO x ) are nodes and bonding units in the char, PO x bonds to the hydrocarbon fragments through P-O-C bonds. Particularly, pyrolysis molecules of suture and rupture of char (C n H 2n+2 PO 4 , m/z=168, 139 and 124) are first discovered. This work booms the path and lays the foundations for the photothermal and fire safety of BP nanocomposites.