Facile and green approach to the synthesis of zeolitic imidazolate framework nanosheet-derived 2D Co/C composites for a lightweight and highly efficient microwave absorber.

The two-dimensional Co/C composites derived from nanosheet-like ZIF-67 (Co-based zeolitic imidazolate framework) precursor was synthesized by a facile and green method. The microstructure, graphitization degree, magnetic properties and microwave absorption properties of two-dimensional Co/C composites varied in sensitivity with the pyrolysis condition. The one prepared at 700 °C exhibited the better microwave absorption performance in the terms its absorbing capability, matching thickness and the bandwidth for effective absorption. Adding only 10 wt% the as-prepared two-dimensional Co/C composites into paraffin, the maximum reflection loss reached -39.3 dB and the corresponding effective bandwidth was observed to broaden to 5.1 GHz (9.7-14.8 GHz) with matching thickness of 2.4 mm, which is superior to that of typical rhombic dodecahedron ZIF-67 derived composites absorber. Theoretical analysis reveals that dielectric loss are responsible for their excellent performance, i.e., the interfacial polarization processes and dipole polarization. Furthermore, the magnetic loss (natural ferromagnetic resonance and exchange resonance) and the wave interference cancellation model also contribute to microwave absorption. It is expected that this work may provide a systematic guideline to design lightweight and highly efficient microwave absorber.