MOFs-derived flower-like cobalt@carbon multiscale hierarchical composites with effective microwave absorption in the low frequency range

The wave-absorbing materials are kinds of special electromagnetic functional materials and have been widely used in electromagnetic pollution control and military fields. In-situ integrated hierarchical structure construction is thought as a promising route to improve the microwave absorption performance of the materials. In the present work, layer-structured Co-MOFs precursors were grown in-situ on the surface of carbon fibers with the hydrothermal method. After annealed at 500 °C under Ar atmosphere, a novel multiscale hierarchical composites (Co@C/CF) were obtained with the support of carbon fibers, keeping the flower-like structure. SEM, TEM, XRD, Raman and XPS were performed to analyze the microstructure and composition of the hierarchical structure, and the microwave absorption performance of the Co@C/CF composites were investigated. The results showed that the growth of the flower-like structure on the surface of carbon fiber was closely related to the metal-to-ligand ratio. The optimized Co@C /CF flower-like composites achieved the best reflection loss of -55.7dB in the low frequency band of 6-8 GHz at the thickness of 2.8mm, with the corresponding EAB of 2.1 GHz. The EAB of 3.24 GHz was achieved in the high frequency range of 12-16 GHz when the thickness was 1.5 mm. The excellent microwave absorption performance was ascribed to the introduction of magnetic components and the construction of the unique structure. The flower-like structure not only balanced the impedance of the fibers themselves, but also extended the propagation path of the microwave and then increased the multiple reflection losses. This work provides a convenient method for the design and development of wave-absorbing composites with in-situ integrated structure.