Abstract
Layered materials present attractive and important properties due to their two-dimensional (2D) structure, allowing potential applications including electronics, optoelectronics, and catalysis. However, fully exploiting the outstanding properties will require a method for their efficient exfoliation. Here we present that a series of layered materials can be successfully exfoliated into single- and few-layer nanosheets using the driving forces coming from the phase inversion, i.e., from micelles to reverse micelles in the emulsion microenvironment built by supercritical carbon dioxide (SC CO2). The effect of variable experimental parameters including CO2 pressure, ethanol/water ratio, and initial concentration of bulk materials on the exfoliation yield have been investigated. Moreover, we demonstrate that the exfoliated 2D nanosheets have their worthwhile applications, for example, graphene can be used to prepare conductive paper, MoS2 can be used as fluorescent label to perform cellular labelling, and BN can effectively reinforce polymers leading to the promising mechanical properties.
Highlights
Following the advent of graphene in 2004, it was soon recognized that in addition to the composition and arrangement of atoms in materials, dimensionality plays a critical role in determining their fundamental properties[1,2]
For the first time we present a highly facile, efficient and versatile method to exfoliate a series of layered materials by virtue of SC CO2 to switch the phase inversion from micelles to reverse micelles in the emulsion microenvironment
Experimental results demonstrate that the driving force coming from the phase inversion from micelles to reverse micelles is efficient for the exfoliation, and as well as the curvature transition of surfactants and the phase behaviours of micelles in the emulsions can be manipulated by changing formulation variables, such as CO2 pressure and ethanol/water ratio[36,37,38]
Summary
Following the advent of graphene in 2004, it was soon recognized that in addition to the composition and arrangement of atoms in materials, dimensionality plays a critical role in determining their fundamental properties[1,2]. Coleman and other researchers have made a major breakthrough via the sonication-assisted exfoliation in nonvolatile organic solvents or mixed-solvents, like dimethylsulphoxide (DMSO), N-methyl-pyrrolidinone (NMP), N-vinyl-Pyrrolidinone (NVP), to produce monoand few-layer nanosheets[21,22,23,24] It is a simple liquid exfoliation method following the mechanism that the surface energy of the solvent must match that of the solute, but the employment of nonvolatile organic solvents will impede further applications of layered nanomaterials and bring the negative impact to the environment. Further the exfoliated graphene can be used to prepare high-conductive paper, MoS2 nanosheets can be used as broad-spectrum fluorescent label to perform cellular labelling, and BN nanosheets can be used to efficiently reinforce the mechanical properties of polymer This strategy utilizing reverse-micelle-induced method for exfoliation of layered materials has great potential application in electronic, biotechnology, mechanics, energy and information storage, etc
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