Microporous Co/rGO nanocomposites: Strong and broadband microwave absorber with well-matched dielectric and magnetic loss

Microporous Co nanoparticles (NPs) of 22 nm were prepared by dealloying Co−Al NPs, and then were mixed with rGO (5 wt%, 10 wt%, 15 wt%) to produce microporous Co/rGO nanocomposites (MCGNs). The microporous Co NPs with pores width of about 1.6 nm were uniformly dispersed on rGO sheets. As the rGO proportion increases, the saturation magnetization (M_S) of the nanocomposites decreases. The MCGNs exhibit strong and broadband microwave absorption performances. Among these three samples, the sample with 10 wt% rGO shows the smallest minimum reflection loss (RL) value of −108.0 dB with a thickness of merely 1.7 mm, whose absorption bandwidth (RL ≤ −10 dB) is as broad as 8.5 GHz; the sample with 15 wt% rGO possesses the widest absorption bandwidth (RL ≤ −10 dB) of 10.0 GHz with a thickness of 1.9 mm, whose minimum RL is −41.1 dB. The high microwave absorption performance is attributed to the facts that micropores structure can adjust the effective permittivity of the material, and rGO improves the impedance match by promoting dipolar polarization and interfacial polarization processes. An appropriate proportion of rGO also avoids the agglomeration of microporous Co and promotes the exchange resonance to improve the magnetic loss of the MCGNs. The synergistic effect of rGO and microporous Co NPs makes this nanocomposite a promising microwave absorber.