Ultrasound-assisted exfoliation and characterization of 2Dγ-Fe_₂O_₃nanosheets

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 2Dγ-Fe_₂O_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 2Dγ-Fe_₂O_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 2Dγ-Fe_₂O_₃nanoparticle nanosheets and shed light on the structural transformation during the exfoliation process.