Abstract
In this study, we report a simple and efficient two-step method consisting of water-in-oil (W/O) emulsion technique and subsequent annealing process for synthesizing the hollow reduced graphene oxide microspheres embedded with Co nanoparticles (Air@rGO€Co). The microspheres showed good electromagnetic properties because of the coexistence of magnetic loss and dielectric loss to microwaves. The minimum reflection loss (RLmin) value of S1.5 reaches −68.1 dB at 13.8 GHz with a thickness of 2.2 mm, and the absorption bandwidth (lower than −10 dB) is 7.1 GHz covering from 10.9 GHz to 18.0 GHz. More interestingly, we can easily controll the microwave absorbing properties of the microspheres by changing the ratio of the two components in the composites. The excellent electromagnetic match at the corresponding resonance peaks for dielectric and magnetic loss play an important role in improving microwave absorption property. Our study provides a good potential method for preparation of lightweight microwave absorbing materials.
Highlights
We report a simple and efficient two-step method consisting of water-in-oil (W/O) emulsion technique and subsequent annealing process for synthesizing the hollow reduced graphene oxide microspheres embedded with Co nanoparticles (Air@rGO€Co)
The minimum reflection loss (RLmin) value of S1.5 reaches −68.1 dB at 13.8 GHz with a thickness of 2.2 mm, and the absorption bandwidth is 7.1 GHz covering from 10.9 GHz to 18.0 GHz
Our study provides a good potential method for preparation of lightweight microwave absorbing materials
Summary
The synthesis process of Air@rGO€Co microsphere is depicted in Fig. 1, where PVA acts as the binder between AACo particles and GO nanosheets as well as the framework of microsphere, which can be ablated off after calcination in Ar atmosphere. The electromagnetic properties (complex permittivity and permeability) of Air@rGO€Co microspheres were investigated in the frequency range of 1.0−18.0 GHz at room temperature. Based on above EM parameters, the reflection loss (RL) was calculated based on the relative complex permittivity and permeability at a given frequency and thickness according to the following equations[3, 38]: Zin =. Changing the ratio between AACo and the GO will obtained Air@rGO€Co microspheres with different electromagnetic parameter In this way, the adjustable MA property of the composites can be realized. Air@rGO€Co microspheres decrease with the increasing Co contents (Figs S3–S8, Supplementary information), meaning that the dielectric loss was weakened. The S1.5 which could effectively offset the drawbacks of the sole Co nanoparticles or rGO nanosheets, possess moderate impedance matching and splendid attenuation constant as well as the optimal MA properties
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