Challenges in Liquid-Phase Exfoliation of Non-van der Waals Cr₂S₃

Two-dimensional (2D) chromium(III) sulfide has recently attracted increased attention from researchers due to its interesting electronic and magnetic properties and has great potential for application in spintronics and optoelectronics to create sensitive photodetectors. However, the synthesis of 2D Cr₂S₃ crystals is still a challenging task. At present, the mainly used method is vapor deposition, which is a poorly scalable, time-consuming, and expensive process. In this study, liquid-phase exfoliation of bulk chromium sulfide in different solvents (dimethyl sulfoxide (DMSO) and N-Methyl-2-pyrrolidone (NMP)) is demonstrated. It was found that exfoliation using an ultrasonic device with a titanium probe in both solvents produced Cr₂S₃ nanosheets with lateral dimensions ranging from 40 to 200 nm and thicknesses of about 10-15 nm (∼6-10 unit cells). Experiments have shown that under liquid-phase exfoliation (LPE) conditions, partial degradation and oxidation of solvents are observed, which has a significant effect on the exfoliation of chromium sulfide. In particular, it leads to partial hydrolysis and oxidation of 2D Cr₂S₃, as well as adsorption of solvent degradation and polymerization products on its surface, and affects the properties of the obtained material. These observations seem to be important in view of the further use of NMP and DMSO for the exfoliation of bulk nonlayered van der Waals crystals by LPE. A new understanding of the exfoliation process of non-van der Waals compounds based on the chemical interaction between the dispersion medium and the dispersed phase is proposed.