Improveament of multiple attenuation and optimized impedance gradient for excellent multilayer microwave absorbers derived from two-dimensional metal–organic frameworks

Low-dimensional carbon matrix magnetic nanocomposites exhibit expansive prospects as lightweight microwave absorbers due to their large specific surface area and multiple attenuation characteristics. The two-dimensional (2D) flaky MOF-derived porous nanocomposites are synthesized successfully by acid etching and subsequent thermal reduction. An in-depth study of composition and flaky porous structure shows that acid etching increases multiple interfaces and carbon defects, proving beneficial for improving multiple interfacial polarization and relaxation polarization loss. In addition, the generated ferromagnetic products (Ni 4 N, CoFe) are beneficial in improving the magnetic loss ability. More importantly, the multilayer impedance gradient design optimizes the impedance matching characteristic. As a result, the prepared bilayer absorbing coating exhibits excellent microwave absorption properties with an effective absorption bandwidth (EAB) of 6.32 GHz at a thickness of 2.5 mm with a filling amount less than 15 wt%. When the total thickness is 3 mm, it can exhibit the widest EAB of about 7.1 GHz and the minimum reflection loss ( RL min ) value of about −54.5 dB. The RCS simulation shows that the multilayer coatings exhibit good microwave scattering and absorption ability under different pitching angles, proving potential candidates for excellent microwave absorbers.