Constructing hierarchical hollow CuS microspheres via a galvanic replacement reaction and their use as wide-band microwave absorbers

In this study, hollow three-dimensional CuS hierarchical microspheres were prepared via a facile galvanic replacement reaction. The hollow flower-like CuS microspheres were characterized by XRD, Raman, XPS, SEM and TEM techniques, which revealed that numerous nanoflakes were self-assembled to construct hollow flowers. Based on time-dependent experiments, a plausible formation mechanism (galvanic replacement reaction) was proposed. Paraffin-based composites, containing 50 wt% hollow CuS, exhibited outstanding microwave absorption capabilities, which were attributed to the suitable impedance match and dielectric loss. The minimal reflection loss was -17.5 dB and the effective bandwidth was 3.0 GHz with thin absorber thickness of 1.1 mm. In addition, we put forward a novel solution to evaluate the microwave absorption efficiency. The high efficiency microwave absorption properties originate from the electric/dielectric polarization and unique hollow flower-like structure. The hollow structures can adjust the dielectric properties to obtain good impedance matching. Moreover, the two-dimensional flakes and hollow flowers can induce more multiple reflection and scattering, which consumes more microwave energy. This study has led to a novel useful method for the design of hollow structures used as high efficiency microwave absorbers.