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

The development of high-performance, easily tunable, and multifunctional electromagnetic materials remains a challenge in the field of microwave absorption. To address key issues such as impedance mismatch and insufficient loss capacity in absorbers, this paper proposes a dual-strategy approach based on solvent-mediated competitive coordination and reaction-driven modulation for the design and preparation, a tunable Zeolitic Imidazolate Framework-67 (ZIF-67) shell was successfully constructed on the surface of flake carbonyl iron (FCI). FCI@ZIF-67-d achieves an effective absorption bandwidth (EAB) of 8.37 GHz at 1.59 mm, while FCI@ZIF-67-s exhibits a minimum reflection loss (RLmin) of −54.00 dB at 4.48 GHz. In addition, the combination of first-principles (DFT) and electromagnetic finite element simulation techniques with experimental results has further elucidated the loss mechanism of FCI@ZIF-67. When the shell transitions from a three-dimensional (3D) dodecahedral structure to a two-dimensional (2D) nanosheet, the nanosheet shell effectively releases the π–π* bonds constrained within the 3D 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. This research provides a clear physical framework for understanding microwave absorption through dimensional control and introduces a low-temperature, frequency-customizable design strategy for advanced absorbers.