Structural and dielectric characteristics of CoFe2O4/nitrogen-enriched reduced graphene oxide composites via a one-pot solvothermal method

Abstract

A one-pot solvothermal method was employed to synthesise nanocrystalline CoFe₂O₄ (CFO) and CoFe₂O₄/Nitrogen-doped reduced graphene oxide (CFO/N-rGO) nanocomposites with varying graphene oxide (GO) contents ranging from 0 to 80 mg. Comprehensive structural analyses viz., X-ray diffraction (XRD), Fourier transform infrared (FTIR) studies,  high resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray analyses (EDX), and Raman spectroscopy confirmed the high purity of the nanocomposites, along with the presence of diverse functional groups and phonon modes associated with both GO and CoFe₂O₄. The XRD analysis revealed a crystallite size of approximately ~ 24 nm for the CFO/N-rGO80 composite. SEM imaging demonstrated the porous microstructure and agglomeration of ferrite nanoparticles. Raman spectroscopy identified distinct symmetric and asymmetric stretching modes corresponding to tetrahedral and octahedral cations, as well as new vibrational modes attributed to nitrogen-doped reduced graphene oxide (N-rGO) integration. X-ray photoelectron spectroscopy (XPS) detected Co⁺² and Fe⁺³ within the tetrahedral and octahedral sites of the ferrite lattice alongside nitrogen dopants on graphene oxide. Magnetic measurements revealed a gradual reduction in saturation magnetization (M_s) from 74.38 emu/g for the CFO sample (0 mg GO) to 68.40 emu/g for the CFO/N-rGO80 sample (80 mg GO). The improved dielectric properties of the CoFe₂O₄/Nitrogen-doped reduced graphene oxide (CFO/N-rGO) composite were examined through dielectric studies across a frequency range of 1 Hz to 20 MHz. The CFO/N-rGO80 composite demonstrated the highest dielectric constant (εʹ = 53.21) and dielectric loss (εʹʹ = 37.60) at 1 MHz, along with the maximum AC conductivity (σ = 2.10 × 10⁻³ Sm⁻¹). These results highlight the enhanced dielectric properties of the nanocomposites due to the incorporation of N-rGO into CFO, which could be a promising material for high dielectric energy storage and microwave-absorbing materials.