Controlled Exfoliation of MoS₂ Crystals into Trilayer Nanosheets

Abstract

The controlled exfoliation of transition metal dichalcogenides (TMDs) into pristine single- or few-layer nanosheets remains a significant barrier to fundamental studies and device applications of TMDs. Here we report a novel strategy for exfoliating crystalline MoS2 into suspensions of nanosheets with retention of the semiconducting 2H phase. The controlled reaction of MoS2 with substoichiometric amounts n-butyllithium results in intercalation of the edges of the crystals, which are then readily exfoliated in a 45 vol % ethanol-water solution. Surprisingly, the resulting colloidal suspension of nanosheets was found (by electron microscopy and atomic force microscopy) to consist mostly of trilayers. The efficiency of exfoliation of the pre-intercalated sample is increased by at least 1 order of magnitude relative to the starting MoS2 microcrystals, with a mass yield of the dispersed nanosheets of 11-15%.

A simple electrochemical route to metallic phase trilayer MoS2: evaluation as electrocatalysts and supercapacitors

“…Previous works showed that the measured flake thicknesses for solution/chemically exfoliated MoS 2 deposited on Si/SiO 2 varied between 1.1 and 1.9 nm for monolayer and ∼5 nm for trilayer nanosheets. 15,36 The deviations from their theoretical thickness (0.615 nm for monolayer) were attributed to the presence of adventitious adsorbates, trapped or adsorbed water molecules and flake-substrate equilibrium separation. 15,35 In the case of 1T phase in particular, the excess negative charge formed due to the electron donation from lithium is stabilised by adsorption of water molecules on both sides of the nanosheets which then increases the overall thickness of the flake.…”

Nano Ag‐Decorated MoS2 Nanosheets from 1T to 2H Phase Conversion for Photocatalytically Reducing CO2 to Methanol

“…To expand the response range of MoS 2 to UV light, the researchers have explored some methods such as semiconductor recombination, surface reduction, ion doping, precious metal deposition, etc. By now, the most efficient route for preparing the monolayer MoS 2 is the intercalation of the guest material followed by the exfoliation step, the intercalation of Li + converts MoS 2 from the original 2H phase to 1T phase . Therefore, to adjust the band gap of MoS 2 to exhibit its excellent optical properties, phase conversion in the chemical exfoliation of MoS 2 nanosheets has attracted attention.…”

Ionic solutions of two-dimensional materials

“…However, the resultant materials typically react with polar protic solvents, such as water, releasing hydrogen gas between the layers. In some materials this vigorous reaction can be harnessed to drive exfoliation, but this approach yields meta-stable and heterogeneous dispersions 19,26,27,28 . Some progress has been made via charging then dispersing graphene in aprotic solvents 29,30,31 , however, sonication 30 or extensive stirring 29,31 was still used for dispersion.…”