Rational construction of Co@C polyhedrons covalently-grafted on magnetic graphene as a superior microwave absorber

Lightweight and high-efficiency microwave absorbers have received considerable focus in military as well as civil fields. In this work, a unique method was employed to synthesize the Co@C polyhedrons covalently-grafted on magnetic graphene derived from MOF via amino reaction, followed by reduction and high-temperature pyrolysis processes. The results demonstrate that after a series of reaction procedures, Co@C polyhedrons are could be successfully linked to the magnetic NRGO by esterification reaction. The microwave absorption outcomes results indicate that the maximum RL of Co@C@NRGO can achieve up to -73.4 dB at 12.1 GHz with an absorber thickness of 2 mm, and the absorption bandwidth (90% absorption efficiency) is as wide as 5.3 GHz (from 9.9 to 15.2 GHz) with the content of 20 wt%. The microwave absorption mechanisms reveal that the covalent bonds between Co@C and NRGO can accelerate the electron transport and facilitate the formation of a conductive network. Meanwhile, the preferable impedance matching, strong attenuation ability, multiple interfacial polarization, and well good complementarities contribute to promoting the promotion of the EM wave absorption capacity of Co@C@NRGO hybrid. Considering the outstanding performance, the as-prepared Co@C@NRGO composite held by covalent bonding can provide an inspiration for the construction of novel microwave absorbers. (C) 2020 Elsevier B.V. All rights reserved.