A dual-strategy approach based on morphological regulation and hierarchical design constructs an ultra-flexible graded rGO/CNT@Fe-MOF sponge for highly efficient microwave absorption

How to increase the thickness of microwave absorbing materials (MAMs) to enhance their microwave absorption performance while maintaining its ultra-flexibility and mechanical durability. Herein, the scheme of graded reduced graphene oxide/carbon nanotube@iron metal-organic framework (rGO/CNT@Fe-MOF) porous sponge is presented. With a thickness of over 1 cm, the sponge achieves the integration of thickness and ultra-flexibility and excellent microwave absorption performance. The sponge not only forms a robust one-dimensional/two-dimensional dual skeleton structure, but also enables interlayer sliding between rGO nanosheets. No damage occurs to the sponge under extreme deformations including folding, high-curvature rolling, bending, twisting, 90% compressive strain, and 10,000 compression-rebound cycles. The ratio of metal ions to organic ligands exhibits a graded distribution among different layers, resulting in each layer forming a different MOF morphology. The synergy between layers, the complex transmission paths, and the multiple loss mechanisms jointly accelerate the dissipation of electromagnetic energy. The graded sponge has an effective absorption bandwidth (EAB) of 8.5 GHz and a minimum reflection loss (RL_min) value of −54.0 dB. After 10,000 compression-rebound cycles, its RL_min remains at −52.1 dB, and the EAB remains at 6.4 GHz. Furthermore, the simulated radar cross-section reduction value of graded sponge is 27.34 dB m².