The rapid development of radar and radio communication technology plays a critical role in enhancing the competitiveness of national defense, while subsequent electromagnetic interference seriously threatens the stealth and information security of military equipment. Consequently, electromagnetic wave absorption (EWA) materials that can eliminate or reduce electromagnetic waves by converting electromagnetic energy into thermal energy or other energy through their own electromagnetic loss mechanism have attracted much attention. Nevertheless, the development of EWA materials is still a challenge to simultaneously satisfy efficient microwave absorption and excellent anticorrosive performance in the case of the complex and changeable marine military environment. Reduced graphene oxide (rGO) with a unique sheet structure, a great chemical stability and a high electrical conductivity can extend the diffusion path of corrosive media and provide conductive loss, which is an excellent candidate for anticorrosion and wave absorption material. To improve the environmental adaptability of EWA materials for practical applications, constructing nanocomposites via combining rGO and MOFs derivatives is an effective strategy to achieve significant EWA and anticorrosion properties. In this paper, metal nanoparticle uniformly loaded carbon skeleton-rGO composites were prepared with MOFs as precursors to improve the impedance matching and EWA performance via utilizing the synergistic effect of magnetic nanoparticles and dielectric rGO. In addition, a theoretical and experimental reference for the development of new multifunctional materials with a high-efficiency electromagnetic wave absorption and an anticorrosion performance was also provided.

For the preparation of Ni/Zn/NC@rGO nanocomposites, graphene oxide (GO) was prepared by a modified Hummer method. Also, white ZIF-8 precursor powder was obtained via dissolving zinc nitrate in 2-methylimidazole solution in methanol system. Meanwhile, nickel nitrate was dissolved into ZIF-8 precursor powder, and GO with different mass ratios of nickel nitrate was added. Finally, the obtained powder was treated at a high temperature to obtain Ni/Zn/NC@rGO nanocomposites. The composition of Ni/Zn/NC@rGO nanocomposites was determined by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The magnetic properties of the composites were measured via hysteresis curves. The microstructures of the nanocomposites were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electromagnetic parameters of Ni/Zn/NC@rGO nanocomposites were examined by a vector network analyzer. The dynamic potential polarization of bare carbon steel, carbon steel coated with pure epoxy resin coating, carbon steel coated with 3% (in mass fraction) doped Ni/Zn/NC epoxy resin (Ni/Zn/NC/EP), and carbon steel coated with 3% doped Ni/Zn/NC@rGO epoxy resin (Ni/Zn/NC@rGO/EP) were analyzed by an electrochemical workstation for three times to ensure the accuracy of the results.

The XRD patterns of Ni/Zn/NC and Ni/Zn/NC@rGO nanocomposites show a crystalline facet C(002) of rGO as well as crystalline facets (111), (200) and (220) of Ni metal, indicating that Ni²⁺ is reduced to magnetic Ni monomers at a high temperature. The XPS spectra show that the Ni/Zn/NC@rGO nanocomposites consist of elements C, N, Ni, O and Zn. Ni/Zn/NC@rGO-1∶1 nanocomposite has the maximum degree of graphitization and more structural integrity, possibly due to the promotion of wave absorption and anticorrosion properties. Besides, the SEM and TEM images of Ni/Zn/NC@rGO nanocomposites reveal that the nanocomposites have a large number of pore structures, which allow electromagnetic waves to be dissipated through multiple reflection and scattering. Furthermore, Ni nanoparticles are uniformly dispersed on rGO nanosheets, and the multiple interfaces formed lead to the polarization relaxation phenomenon, which is beneficial for the attenuation of electromagnetic waves through polarization loss.

Ni/Zn/NC@rGO-1∶1 nanocomposite has the maximum electromagnetic wave storage and attenuation capabilities, which can be attributed to that the interface polarization induced by the rGO multilayer structure and the uniformly dispersed Ni nanoparticles and the rGO sheets, as well as the dipole polarization originated from the defects created by N atoms doping during the pyrolysis process. Moreover, the imaginary part of the complex permittivity of Ni/Zn/NC@rGO-1∶1 shows slight fluctuations, indicating that the existence of multiple polarization relaxation processes, which is also confirmed by the Cole-Cole semicircle plots. As a result, Ni/Zn/NC@rGO-1∶1 exhibits the optimum EMA performance. The minimum reflection loss value (RL_min) is -63.70 dB with a matching thickness of 1.67 mm, and the effective absorption bandwidth (RL<-10 dB) reaches 5.36 GHz at the thickness of 1.63 mm. The synergistic benefits of magnetic nanoparticles and dielectric rGO optimize the impedance matching characteristics of Ni/Zn/NC@rGO-1∶1 sample, while the porous structure and abundant interface polarization effectively improve the attenuation constant of the sample.

Compared with carbon steel of other coating samples, Ni/Zn/NC@rGO/EP coating sample possesses a higher corrosion potential and a lower corrosion current, thus showing the most excellent anticorrosion performance. Ni/Zn/NC@rGO nanoparticles fill the micropores of the epoxy resin, which can effectively inhibit the infiltration of corrosive ions. In addition, the unique sheet structure of graphene is also easy to stack and thereby extend the diffusion pathway of corrosive media to achieve the purpose of improving the anticorrosion performance.

Ni/Zn/NC@rGO nanocomposites derived from MOF were synthetized via co-precipitation and pyrolysis processes., The outstanding impedance matching and microwave attenuation ability was realized via adjusting the mass ratios between the Ni source and GO. At a mass ratio of 1∶1, the effective absorption bandwidth and the RL_min values were 5.36 GHz and -63.70 dB with the thicknesses of 1.63 mm and 1.67 mm, respectively, which could be attributed to that the porous structure provide transmission paths for multiple reflections and scattering of electromagnetic waves, as well as multiple interfaces bring more polarization loss. In particular, the graphene layer structure also extended the diffusion path of the corrosive medium, resulting in a higher corrosion potential and a lower corrosion current in Ni/Zn/NC@rGO-doped nanocomposite coatings. This study provides a reference for the development of efficient anticorrosion and EWA materials, which could have a promising application in the field of marine environment.