Abstract: Macroscopic morphology engineering and micro-/nano-component regulation are the essential routes for addressing the existing performance drawbacks for electromagnetic wave absorbing materials (EMAWs). Owing to their tunable compositions and structural configurations, metal-organic frameworks (MOFs) represent attractive materials for constructing high-efficiency wave absorbers. In this study, a structure-component integrated strategy was proposed using a ZIF-8@ZIF-67 core-shell precursor. A composite of hollow B,N co-doped carbon nanocages loaded with cobalt nanoparticles (Co/BCN) was synthesized through room-temperature epitaxial growth and melamine/boric acid-assisted pyrolysis. The obtained material retains an open rhombic dodecahedral hollow framework and enables B,N co-doped carbon nanotubes to grow in-situ over its outer surface, forming a distinctive hierarchical composite architecture. Systematic investigations demonstrate that boron-nitrogen co-doping enhances the defect density of the carbon framework, promotes multiple Debye relaxation, increases interface polarization and conduction loss, and optimizes impedance matching. The as-prepared Co/BCN-0.15 sample demonstrates superior microwave dissipation capability. Under the condition of 10 wt% filler loading and 1.9 mm absorber thickness, the material can attain −61.71 dB minimum reflection loss, while its effective absorption bandwidth can expand up to 5.04 GHz. Such remarkable absorption behavior stems from combined factors of multiple scattering within the hierarchical hollow architecture, defect-induced polarization induced by B and N sites, the Co/C conductive network, and well-optimized impedance matching. This work proposes a viable approach to fabricate MOF-derived carbon-based composites with reduced thickness, high efficiency, and broadband electromagnetic wave absorption.

Key words: Metal-organic frameworks, Nanocages, Core-shell structure, Carbon nanotubes