MOF-derived yolk-shell Ni/C architectures assembled with Ni@C core-shell nanoparticles for lightweight microwave absorbents

Yolk-shell Ni/C microspheres composed of Ni@C core-shell nanoparticles were successfully fabricated by decomposing a Ni-based metal-organic framework (Ni-MOF) at 500 degrees C and 600 degrees C. The Ni-MOF with a yolk-shell structure was prepared by a solvothermal method with an appropriate molar ratio of Ni(NO3)(2)center dot 6H(2)O to C9H6O6 in the presence of PVP. The degree of crystallization of Ni and C was improved by increasing the pyrolysis temperature, which resulted in enhanced complex permittivity and optimized impedance matching of Ni/C microspheres for damping microwave. Meanwhile, the attenuation coefficient of Ni/C microspheres increased with the increment in pyrolysis temperature. The yolk-shell Ni/C microspheres obtained at 600 degrees C exhibited the optimal reflection loss (RL) reaching-39 dB with a bandwidth of 3.8 GHz (RL <-10 dB) at a thin matching thickness of 1.8 mm. The integrated bandwidth can achieve 12.3 GHz covering Ku-band (12-18 GHz), X-band (8-12 GHz), and most of C-band (5.7-8 GHz) with an appropriate thickness of 1.4-3.9 mm. Such excellent microwave absorption performance can be attributed to the synergistic effect of the magnetic and dielectric losses of Ni/C microspheres due to natural resonance, dipolar polarization and multiple interfacial polarizations at a unique yolk-shell interface, achieving the optimization of impedance matching and microwave attenuation. This work demonstrates that Ni/C microspheres with a desirable yolk-shell structure are potential candidates for the application in microwave absorption field.