δ-MnO2 Nanoflowers and Their Reduced Graphene Oxide Nanocomposites for Electromagnetic Interference Shielding

The present work is focused on room-temperature reduction by subjecting reduction of an aqueous KMnO4 and KMnO4/graphene oxide (GO) dispersion by Fehling solution B in one step to form delta-MnO2, exhibiting hierarchical nanoflowers and their nanocomposites (delta-MnO2/reduced graphene oxide). This was followed by their characterization by X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), surface area measurements, and DC conductivity. The effect of the concentration of a reducing agent on the morphological evolution of delta-MnO2 has also been proposed. Further, these materials were also investigated for their performance in electromagnetic interference (EMI) shielding efficiency (SE) in the frequency range of 2-8 GHz. These findings showed the highest total shielding efficiency (similar to 39 dB) of the (delta-MnO2/reduced graphene oxide (RGO)-1.0 nanocomposite consisting of 5.5 wt % RGO following reflection as a dominant mechanism. Such excellent performance was attributed to the poor impedance matching between MnO2/RGO, the formation of an interconnected conducting network, and interfacial polarization. It is anticipated that delta-MnO2/RGO nanocomposites synthesized by a simple room-temperature reaction in one step could be promising candidates as lightweight and high-performance EMI shielding materials for multifaceted applications.