A novel dual-functional EMOFs containing azide ligands: Synergistic enhancement on ignition and combustion properties of boron powders

The applications of boron-based (B) fuels in propulsion and weapon systems are hindered by inefficient combustion and harsh ignition conditions of B particles. Dual-functional energetic metal-organic frameworks (EMOFs) were synthesized on B surface by incorporating azide ligands as secondary ligands to improve the thermal and combustion properties of B particles. Polydopamine (PDA) interfacial layer was constructed between B and EMOFs to strengthen the interface interaction and facilitate the processes of mass and heat transfer. The mechanisms of EMOFs in eliminating the negative effects of oxide film and enhancing B combustion were analyzed. The results illustrate that the expansion of flame front is driven by the micro-explosion effect of azide ligands, and the flame height increases from 0.46 to 67.9 mm. Concurrently, the generated metal oxides alter the oxygen diffusion pathway by adhering to B surface, thereby significantly enhancing the oxidation process of B. The combustion efficiency of B increases from 60.7 % to 80.4 %, the oxidation temperature lowers by 77 °C, and the flame radiation intensity enhances by approximately 29 %. Crucially, the azide ligands and residual metal oxides exhibit different functions. The azide ligands exhibit the functions of ignition sensitization and micro-explosion at the combustion interface, while the adherent metal oxides promote the efficient oxidation of B particles along two distinct pathways. This innovative strategy of integrating azide ligands and metal oxides offers a novel direction for enhancing the energy release performance of B-based fuels.