Ultrasound-assisted exfoliation and characterization of 2D γ -Fe ₂ O ₃ nanosheets

Abstract The intrinsic strong bonding network limits controlled two-dimensional (2D) nanosheet exfoliation of non-van der Waals materials. We report here the successful stabilization and 2D nanosheet exfoliation of 2D γ -Fe ₂ O ₃ (maghemite) nanosheets through the application of ultrasound-assisted liquid-phase exfoliation with the aid of cetyltrimethylammonium bromide (CTAB) as the stabilizing agent. Atomic force microscopy (AFM) confirms the existence of ultrathin nanosheets of thickness ∼0.5–2 nm corresponding to the monolayer and few-layer structures. X-ray diffraction verifies the broadening of the peaks and the characteristic shifting of the peaks of compressive strain in the nanosheets of the exfoliated structure. X-ray photoelectron spectroscopy corroborates the existence of hydroxyl (–OH) functional groups on the nanosheet surfaces and the existence of the CTAB molecules that achieve stabilization through electrostatic and steric interactions. A prominent peak in the 200–250 nm region with the extended broad absorption to the visible region is observed through the application of UV–Vis spectroscopy and it is assigned to defect states formed during the process of exfoliation. Such structural and surface modifications are expected to modify the 2D γ -Fe ₂ O ₃ ’s physical and chemical properties, making it a promising material for a wide range of applications in materials science, nanotechnology, and environmental or energy-related technologies. We demonstrate here an effective route to the production of processable and stable 2D γ -Fe ₂ O ₃ nanoparticle nanosheets and shed light on the structural transformation during the exfoliation process.