Nest-like hollow Cu-doped Co/CoO/C microspheres derived from spherical Co-ZIF with controllable microwave absorption performance

Abstract

Spherical Co-ZIF-derived nest-like hollow Cu-doped Co/CoO/C microspheres are obtained by a high-temperature calcination treatment, where a facile mixing method is used to synthesize the Cu/Co-ZIF precursor. During the carbonization process at high temperatures, carbon nanotubes are in-situ grown on the microspherical surface to form interlinked conduction networks. Adjusting the calcination temperature can effectively control the degree of graphitization, leading to the diverse electromagnetic performance. When the calcination temperature is 700 °C, an optimal microwave absorption (MA) property is obtained for sample S700 at 25 wt% filler loading ratio. Herein, the values of the minimum reflection loss (RLmin) and the effective absorption bandwidth (EAB) attain −52.73 dB at 2.51 mm and 6.16 GHz at 2.31 mm, respectively. Meanwhile, when the filler loading increases to 30 wt%, RLmin and EAB for sample S600 achieve −60.02 dB at 1.59 mm and 5.76 GHz at 1.90 mm, respectively. In fact, the superior electromagnetic parameters are achieved under the comprehensive action of the specific morphology, microstructure and graphitization. Further, the applicable filler loading ratio, appropriate impedance matching and moderate magnetic/dielectric loss of the absorbers are the advantageous factors to improve their MA behavior. Our work offers an effective strategy to synthesize MOF-derived magnetoelectric composites with controllable MA performance, and the as-obtained composites can serve as the ideal microwave absorbers at 2 ∼ 18 GHz frequency range.