Tunable Low-Frequency Microwave Absorption in Flaky Carbonyl Iron via 3D-To-2D ZIF-67 Shell Engineering

Current research on wave-absorbing materials predominantly focuses on exploring novel MOF precursors and constructing complex microstructures. However, significant challenges remain in deeply optimizing the performance of existing materials through dimensional regulation, particularly in addressing the difficulties of impedance mismatch and insufficient loss capability in 2–8 GHz. Based on a dual strategy of solvent-mediated competitive coordination and reaction-driven regulation, this study successfully constructed a tunable ZIF-67 shell layer on the surface of flake carbonyl iron (FCI). When the shell transitions from a three-dimensional dodecahedral structure to a two-dimensional nanosheet, the nanosheet shell effectively releases the π–π* bonds constrained within the three-dimensional framework, significantly enhancing the conduction and dielectric polarization capabilities of the material. This enhancement effect strongly couples with the magnetic loss provided by the FCI core, synergistically optimizing impedance matching and attenuation mechanisms in the low-frequency range. Notably, FCI@ZIF-67-d achieves an effective absorption bandwidth of 8.37 GHz at 1.59 mm, while FCI@ZIF-67-s exhibits a minimum reflection loss of −54.00 dB at 4.48 GHz. Moreover, by adjusting the content of the two-dimensional shell, its absorption peak can be tuned within the range of 2.48 to 7.63 GHz. This research not only provides a clear physical framework for understanding and enhancing microwave absorption performance from the perspective of dimensional control, but also offers a novel approach for designing absorbers with customizable frequencies that do not require high-temperature processing.