Surfactant-Free Polar-to-Non-Polar-Phase Transfer of Exfoliated MoS2 Two-Dimensional Colloids

TL;DR

This paper demonstrates a surfactant-free method to transfer exfoliated MoS2 nanosheets from polar to non-polar solvents, enabling broader functionalization and processing options for 2D materials.

Contribution

It introduces a novel surfactant-free phase transfer technique for MoS2 nanosheets from polar to non-polar solvents, expanding their application potential.

Findings

Successful transfer of MoS2 nanosheets to chloroform without surfactants

Colloidal stability depends on nanosheet size in non-polar solvent

Enables subsequent functionalization in non-polar media

Abstract

Exfoliation of lamellar materials into their corresponding layers represented a breakthrough, due to the outstanding properties arising from the nanometric thickness confinement. Among the cleavage techniques, liquid-phase exfoliation is now on the rise because it is scalable and leads to easy-to-manipulate colloids. However, all appropriate exfoliating solvents exhibit strong polarity, which restrains a lot the scope of feasible functionalization or processing of the resulting flakes. Here we propose to extend this scope, demonstrating that nanosheets exfoliated in a polar medium can be properly dispersed in a non-polar solvent. To that purpose, we prepared suspensions of molybdenum disulfide flakes in isopropanol/water and developed a phase transfer of the nanosheets to chloroform via precipitation and redispersion/centrifugation sequences, without any assisting surfactant. The colloidal stability of the nanosheets in chloroform was found to be governed by their lateral dimensions and, although lower than in polar media, proved to be high enough to open the way to subsequent functionalization or processing of the flakes in non-polar medium.