Impact of Pretreatment of the Bulk Starting Material on the Efficiency of Liquid Phase Exfoliation of WS2

Abstract

Liquid phase exfoliation (LPE) is widely used to produce colloidal dispersions of nanomaterials, in particular two-dimensional nanosheets. The degree of exfoliation, i.e., the length to thickness aspect ratio was shown to be intrinsically limited by the ratio of in-plane to out-of-plane binding strength. In this work, we investigate whether simple pretreatment of the starting material can be used to change the in-plane to out-of-plane binding strength through mild intercalation to improve the sample quality in sonication-assisted LPE. Five different pretreatment conditions of WS2 were tested and the dispersions size-selected through centrifugation. From optical spectroscopy (extinction, Raman, photoluminescence), information on nanosheet dimension (average lateral size, layer number, monolayer size) and optical quality (relative photoluminescence quantum yield) was extracted. We find that the pretreatment has a minor impact on the length/thickness aspect ratio, but that photoluminescence quantum yield can be increased in particular using mild sonication conditions. We attribute this to the successful exfoliation of nanosheets with a lower degree of basal plane defectiveness. This work emphasizes the complexity of the exfoliation process and suggests that the role of defects has to be considered for a comprehensive picture.

Controlling the Hierarchical Structures of Molybdenum Disulfide Nanomaterials via Self-Assembly of Supramolecular Polymers in Water

“…Chemical vapor deposition, solvothermal synthesis, and micromechanical cleavage methods are high-energy, time-consuming processes and are thus unsuitable for fast, economical, large-scale production of few-layer MoS 2 nanosheets. Recently, LPE using organic solvents with comparable surface tension to MoS 2 was reported as a simple technique for mass production of high-quality 2D nanosheets with good dispersion stability. − The LPE process depends on favorable interactions between solvent molecules and the layered nanomaterials to stabilize the scattered components, while an external force is used to exfoliate the layers. As a result, only certain solvents, such as 1,2-dichlorobenzene, N -methyl-2-pyrrolidone, dimethyl sulfoxide, and N , N -dimethyl formamide, have been successfully employed for the exfoliation and dispersion of layered nanomaterials .…”

The Effectiveness of Cyrene as a Solvent in Exfoliating 2D TMDs Nanosheets

“…A parameter that was considered as an indicator to evaluate the ease of exfoliation using LPE was the L/N ratio [ 56 , 62 ]. The higher the L/N ration is, the easier it is to obtain high-quality 2D NSs using LPE from pristine bulk materials.…”

Wet-jet milling exfoliated hexagonal boron nitride as industrial anticorrosive pigment for polymeric coatings

“…steel) [48], failure of ultra-thin coatings [49], poor adhesion or delamination [50], friction-induced damage [51] or problems related with the upscaling of monolayer growth techniques (e.g. the difficulty of obtaining defect-free nanosheets [52,53] or achieving large-scale homogeneity [54]) from laboratory to industry [55]. To overcome these limitations, liquid-phase exfoliation (LPE) methods [56] have been established as eligible techniques to scale up the production of 2D h-BN in liquid media [57], providing dispersions that can be directly used to formulate advanced composites with polymers by solution blending methods [58].…”