A nanostructure of reduced graphene oxide and NiO/ZnO hollow spheres toward attenuation of electromagnetic waves

A nanostructured composite composed of reduced graphene oxide (rGO) and NiO/ZnO hollow spheres was prepared via an in situ reaction involving pyrolysis and surface modification of a heterobimetallic Ni–Zn metal-organic framework with amine-functional group. The rGO sheet was successfully grafted on the surface of NiO/ZnO. The hybrid displayed excellent microwave absorbing performance in a polystyrene matrix. The optimal minimum reflection loss reached −42.5 dB at 13.2 GHz at a coating thickness of only 2.15 mm with a 4.5 GHz effective absorption frequency bandwidth, corresponding to a reflection loss of less than −10 dB (90% absorption). The grafting of rGO not only resulted in a hybrid composite with a larger contact area, but also benefited the synergistic effects with NiO/ZnO to endow the electromagnetic wave absorbing performance. Herein, the effective absorption capability of rGO@NiO/ZnO mainly contributed to the enrichment of interfacial polarization, dipole polarization, and dielectric loss followed by multiple reflection and scattering generated from heterogeneous components in the composite. This work is expected to provide a promising method for the development of high-performance microwave absorbers staring from rGO/heterobimetallic MOFs composites.