Facile synthesis of NiCo2 nanoparticles grown on rice husk waste-derived porous carbon for high-efficiency microwave absorption

Herein, rice husk waste-derived porous carbon decorated with NiCo2 nanoparticles (NiCo2/C) was simply prepared by impregnation method combined with an annealing process. From the SEM images, 0-dimensional (0D) NiCo2 nanoparticles (NPs) are uniformly dispersed on the surface of three-dimensional (3D) porous rice husk carbon (PRC). The porous carbon skeleton with high graphitization not only extends the propagation path of electromagnetic waves, but also improves the conductive loss. Upon increasing the NiCo2 NPs content, the conductive loss initially decreases and then aggrandizes, while the polarization relaxation shows a monotonic increase. Benefiting from the specific structure (0D NiCo2 nanoparticles decorated 3D porous carbon construction) and the synergistic effect of excellent attenuation capacity and good impedance matching, NiCo2/C exhibits remarkably increased microwave absorption capability relative to pure PRC. By controlling the content of metallic NiCo2 NPs, the minimum RL of most samples exceeds −20 dB (＞99% attenuation) in wide EM wave ranges (4.64–18 GHz) with the variation of the absorber thickness from 1.0 to 5.0 mm. In detail, the reflection loss (RL) value is up to −55.62 dB with a thickness of 3.57 mm, and the effective absorption bandwidth (EAB) reaches 4.24 GHz with a thin thickness of only 1.5 mm. This work gives a new guideline for the development of magnetic biomass carbon composite absorbers.