Synergistic effect of niobium oxide and cobalt on electromagnetic properties of dodecahedron-carbon composites

Abstract

Here, we report niobium pentoxide/niobium dioxide/cobalt/porous carbon (Nb2O5/NbO2/Co/C) nanocomposites synthesized through carbonization of zeolitic imidazolate framework-67/niobium pentoxide (ZIF-67/Nb2O5) precursor. It was showed that Nb2O5 was partially reduced to NbO2 during the carbonization process. With increasing content of Nb2O5, the surface roughness of the composite increased and the magnetic effect decreased. Specifically, the sample with 0.37 ​mmol Nb2O5 exhibited a minimum reflection loss of −64.68 ​dB at 11.76 ​GHz at 2.00 ​mm. The effective absorption bandwidth (RL ​< ​−10dB) of this sample was 4.0 ​GHz (9.44–13.44 ​GHz), covering most of the X-band and part of the Ku-band. This can be attributed to the incorporation of enhanced multiple interface reflections and increased interface capacitive structure, due to the difference in conductivity between the niobium oxides. Furthermore, the presence of the niobium oxides with low permittivity improved the impedance matching of the composites and hence increased the microwave absorption efficiency. The synergic effect of the low permittivity niobium oxides and the magnetic cobalt was responsible for the great enhancement in electromagnetic wave absorption of the composites. This work provides a new method to develop high-performance electromagnetic wave absorbing materials.