  Liquid-phase exfoliation of two-dimensional materials is very attractive for
large-scale applications. Although used extensively, isolating MoS2 layers
(<10) with high efficiency is reported to be extremely difficult. Further, the
importance of soaking has not yet been studied, and the surfactants' role in
stabilizing MoS2 nanosheets is poorly understood1. Herein, we report a novel
approach to exfoliating large quantities of MoS2 via high-pressure (HP)
liquid-phase exfoliation (LPE) in deionized (DI) water. 4 to 7 layers of MoS2
nanosheets were obtained from 60 days-soaked samples and they were found to be
stable in solvents for periods of up to six months. Studies on the effect of
three surfactants, namely sodium dodecyl benzenesulfonate (SDBS), sodium
cholate (SC), and tetra-butyl ammonium bromide (TBAB), indicate that
exfoliation of MoS2 nanosheets in SDBS is highly efficient than the other two
surfactants. The estimated yield reaches up to 7.25%, with a nanosheet
concentration of 1.45 mg/ml, which is one of the highest ever reported. Our
studies also suggest that the nanosheets' concentration and the lateral size
depend on exfoliation cycles, applied pressure and surfactant concentration.
Hydrogen evolution reaction (HER) and ion-transport study show that the
nanosheets prepared by our method are stable in an acidic medium and free from
surfactants. A high hydrogen evolution rate of 30.13 mmol g-1 h-1 was estimated
under ambient laboratory conditions.
