Green exfoliation of 2D nanomaterials using cyrene as a solvent

Abstract

Liquid-phase exfoliation (LPE) is a versatile and scalable method for producing high-quality two-dimensional materials (2DMs). However, commonly used solvents such as dimethylformamide (DMF) or N-methyl-2-pyrrolidone (NMP) are highly toxic, limiting their potential for large-scale industrial applications. In this study, we address this challenge using Cyrene (dihydrolevoglucosenone), a nontoxic and biodegradable solvent, for the exfoliation of several materials, including graphene, MoS₂, WS₂, MoO₃, V₂O₅, and hBN (hexagonal boron nitride). Exfoliation was carried out using low-powered bath sonication, a cost effective and energy efficient method and optimization was conducted to maximize the final concentration of exfoliated material. To assess the potential of Cyrene for LPE, extensive characterization and comparison of the produced 2DMs with their precursors was performed. The highest ink concentrations were observed for MoS₂ (2.6 mg mL⁻¹), followed by hBN (2.3 mg mL⁻¹) and V₂O₅ (1.9 mg mL⁻¹), demonstrating the ability of Cyrene to effectively stabilize a variety of 2D materials in dispersion. Structural and morphological properties of the exfoliated materials were characterized using X-ray diffraction (XRD), Raman spectroscopy, UV-vis spectroscopy, scanning electron microscopy (SEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). XRD patterns mainly showed only one reflection revealing the oriented nature of the materials, with significant broadening of the full width at half maximum (FWHM) compared to the original materials. Also, Raman spectroscopy spectra for graphene showed ratios characteristic of multi-layered structures and SEM imaging revealed a broad distribution of flake sizes. This work highlights the potential of Cyrene as a sustainable and efficient solvent for LPE of diverse 2D materials. The systematic optimization method presented here achieves high dispersion concentrations in a repeatable manner using low-power and ecofriendly means. These findings establish a foundation for the scalable production of 2D inks, enabling their use in advanced applications such as electrode, dielectric and semiconductor layers of electronic devices.