A reliable and highly efficient exfoliation method for water-dispersible MoS2 nanosheet

Since the pioneering work on exfoliated single-layer graphene, layered inorganic nanosheet materials have been widely explored due to their unusual properties with potential applications in energy devices and optical electronics. Among these layered inorganic nanosheets, two-dimensional thin MoS2 nanosheets show extraordinary properties such as the presence of a direct bandgap, magnetism, superconductivity and ferroelectricity. Over the past few years, solution-processed exfoliation methods of layered materials have been extensively studied; most of the exfoliation processes employ organic solvents or use surfactants as well as other functionalization agents. Although pure water is considered as an ideal solvent, however, it is generally believed stable dispersions of water could not be achieved due to poor solubility MoS2 in water. Thus, there are very limited studies for developing of water based MoS2 dispersions. Here we introduce a facile, green and reliable exfoliation method for producing water dispersible MoS2 nanosheet without surfactant. Pure water was used as a solvent and this exfoliation process was achieved by thinning the bulk MoS2 by mechanical force between sandpapers and dispersing it through probe sonication in water. The exfoliated single or few-layered MoS2 nanosheets were characterized by TEM and SEM images. The lateral dimensions of the nanosheets were around 500 nm to 5 gm, the same range as obtained in the organic solvents as reported. Zeta potential measurements indicated that electrical charges may be responsible for the stabilization of the dispersions. Overall, it is concluded that with this exfoliation strategy, water can be used as a useful dispersible solvent for MoS2 nanosheets. Although the stability of the dispersions may not be as high as in organic solvents, the present method could be employed for a number of applications where the dispersions can be produced on site and organic solvents are not desirable. (C) 2018 Elsevier Inc. All rights reserved.