Abstract
High-intensity ultrasound exfoliation of a bulk-layered material is an attractive route for large-scale preparation of monolayers. The monolayer slices could potentially be prepared with a high yield (up to 100%) in a few minutes. Exfoliation of natural minerals (such as tungstenite and molybdenite) or bulk synthetic materials (including hexagonal boron nitride (h-BN), hexagonal boron carbon nitride (h-BCN), and graphitic carbon nitride (g-C3N4)) in liquids leads to the breakdown of the 3D graphitic structure into a 2D structure; the efficiency of this process is highly dependent upon the physical effects of the ultrasound. Atomic force microscopy (AFM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) were employed to verify the quality of the exfoliation. Herein, this new method of exfoliation with ultrasound assistance for application to mono- and bilayered materials in hydrophobic and hydrophilic environments is presented.
Highlights
Mechanical exfoliation, called the ‘scotch tape method’ [1], was the first method used for the preparation of single-layer graphene from natural graphite
We demonstrate simple and low-cost methods for the preparation of single- and few-layered nanosheets of inorganic analogues of graphene, MoS2, WS2, hexagonal boron nitride (h-BN), hexagonal boron carbon nitride (h-BCN), and g-C3N4, using stationary ultrasound waves in a pressurized ultrasonic reactor
The method of exfoliation of inorganic analogues of graphene (IAG) in the alkaline environment is based on a process related to the phenomena of cavitation
Summary
Mechanical exfoliation, called the ‘scotch tape method’ [1], was the first method used for the preparation of single-layer graphene from natural graphite. Rao and Nag [14] described the preparation of WS2 and MoS2 sheets by lithium intercalation followed by exfoliation of the layers by ultrasonication and chemical synthesis, where molybdic acid and tungstic acid, respectively, were treated with an excess of thiourea. Another approach, a mixed-solvent strategy, exploited a low-intensity ultrasonic treatment (ultrasonic bath) for the exfoliation of MoS2, WS2, and BN in ethanol/water mixtures [15]. Lin et al [18] demonstrated that water is effective in the exfoliation of layered h-BN structures with the assistance of an ultrasonic bath and leads to ‘clean’ aqueous dispersions of h-BN nanosheets without the use of surfactants
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