Nitrogen doped graphene nanosheet-epoxy nanocomposite for excellent microwave absorption

Abstract

In the present study, nitrogen doped graphene sheets (NGNs) have been synthesized by solvothermal reaction using cow urine as a natural dopant of N atoms, which is an alternative of highly toxic chemicals with excellent reducing capability. As synthesized NGNs have been characterized by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), UV–visible spectroscopy (UV–vis), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), surface area (Brunauer-Emmett–Teller (BET)) and X-ray photon spectroscopy (XPS). Raman analysis reveals that the reduction of oxygen occurs from graphene oxide (GO) by cow urine, and reaches Raman D to G band intensity ratio of ∼1.23. XPS analysis validates the Raman signature of removal of oxygen functional groups, simultaneously N-atoms are successfully doped into honeycomb lattice, and produces GNs with high C/O ratio of ∼5.25 having N content ∼3.4 at.%. The presence of N atoms produces defect morphology in graphene structure that eventually enhances the overall electrical properties of NGNs. The NGN-epoxy nanocomposites have been fabricated for the investigation of the electromagnetic responses generated exclusively in the X band (8.2–12.4 GHz). A maximum absorption value of −40.8 dB (99.992% absorption) as well as 1.5 GHz of −10 dB effective bandwidth is observed with 2 wt.% of NGNs loadings. The strong microwave absorption is due to the electric, dielectric, interfacial polarization, and nitrogen generated defect polarization canters. Moreover, NGNs with unique disordered structure can regulate the electromagnetic properties to attain the best impedance matching criteria. This investigation opens a novel useful eco-friendly approach for the development of NGNs structure for highly efficient, light weight and low cost microwave absorber.