Surface Defect-Induced Dispersion and Stabilization of Monolayer MoS2 Nanosheets in Polar Solvents

Effective dispersion of two-dimensional (2D) nanosheets in polar solvents is essential for their practical applications. However, ultrathin MoS2 nanosheets produced via mechanical exfoliation or liquid-phase exfoliation lack surface functionalities, posing a significant challenge for achieving a uniform dispersion and good colloidal stability. Here, we investigate the dispersion properties and stabilization mechanism of monolayer MoS2 colloids synthesized via a bottom-up strategy under nanoconfinement. The nanosheets achieve high dispersion concentrations of >1.6 g/L in polar solvents such as water, N-methylpyrrolidone, and 1,4-butanediol, with the highest concentration approaching 10.6 g/L in ethylene glycol, significantly higher than the previously reported concentrations of less than 0.8 g/L for the exfoliated MoS2 nanosheets. The surface free energy of our MoS2 nanosheets is determined to be 48.7 mJ/m2, from which their maximum stable dispersion concentrations in various solvents can be predicted precisely. The high surface free energy can be attributed to the presence of abundant surface defects on the nanosheets, which induce the formation of polar hydroxyl (-OH) groups and increase the negative charge density on the surface, thereby enhancing their dispersibility and colloidal stability. These findings hold significant implications for colloidal applications of 2D MoS2 nanosheets in various fields.