Ultra-flexible, binder-free CNT@[Ni(DHTA)_x(Bpy)_y]_n-MOF composite film for microwave absorption and environmental adaptation

The single coordination mode and weak coordination bonds restrict the comprehensive performance of carbon nanotube (CNT)@Ni-based metal-organic framework (MOF) microwave absorption materials (MAMs), and high-concentration binders further hinder the lightweight development of flexible MAMs. Herein, an ultra-flexible, binder-free CNT@MOF-based composite film (named CF-x/y) is fabricated via combining solvothermal synthesis with directional pressure filtration. This CF-x/y features a robust cross-linked network that can withstand curling, twisting and bending. Under the induction of CNTs, by adjusting the molar ratio of 2,5-dihydroxybenzoic acid to 4,4′-bipyridine, different morphologies of Ni-MOF nanocrystals can be obtained. The optimized CF-1/0.5 exhibits a minimum reflection loss of −50 dB, an effective absorption bandwidth of 7.2 GHz, and a radar cross-section reduction of 20.05 dB m². Density functional theory calculations indicate that electromagnetic energy within CF-x/y is dissipated through a synergistic mechanism of conduction loss and polarization loss. The synergistic effect of Ni–O/Ni–N bonds not only stabilizes the structure but also inhibits corrosion. Meanwhile, the complex architectures extend the diffusion path of corrosive media. This work provides theoretical guidance for designing environmentally adaptable, binder-free, and flexible MAMs.