Preparation of nanosheets via ball milling in the presence of reactive gases

#The present invention relates to nanomaterials, in particular two dimensional nanosheets.

#The invention also relates to the production of nanosheets and to nanosheets produced in accordance with the invention.

#Two-dimensional materials, such as graphene, boron nitride (BN), and transition metal dichalcogenides (TMD) nanosheets, have exceptional electronic, mechanical and physical properties, which are appealing for both fundamental science and practical applications. With successive thickness reduction of the bulk crystals to nanometer scale, the inherent properties of these bulk materials are altered. For example, electrons in graphene behave as Dirac fermions, MoS2 nanosheet undergoes a phase change from an indirect to direct band gap semiconductor, and BN nanosheets exhibit an exceptional ability to adsorb molecules.

#Embodiments of the invention are illustrated with reference to the following non-limiting drawings in which FIGS. 1-12 report results and/or observations discussed in the examples. Further detail about each figure is included below.

#FIG. 1. Different structural changes of graphite under ball milling in different gases. XRD pattern of graphite milled in Ar (a) and NH3 (b) for different times. SEM images showing different morphologies of graphite milled in NH3 (c) and Ar(d) gases. TEM images revealing different structures of the graphite milled for 70 h in NH3 (e, f, g), and in Ar (h). Insets show SAD patterns.

#FIG. 2. Different structural changes of boron nitride (BN) during ball milling in different gases. XRD patterns of hexagonal BN milled in Ar (a) and NH3 (b) for different time. SEM images of BN sample milled for 20 h in Ar (c) and in NH3 (d); TEM images of BN samples after 20 h milling in NH3 (e) and in Ar 20 h (f); SEM image of BN milled for 70 h in NH3 (g) and its TEM image (i).

#In accordance with the invention it has been found that nanosheets may be prepared by reactive ball milling of bulk crystalline materials in a gaseous environment.

#The gas used in the ball milling is believed to participate in chemisorption and/or mechanochemical reactions that favour production of nanosheets by exfoliation of bulk crystalline materials. The exact mechanism by which molecules of the gas interact with the bulk crystalline material is not known. However, various possibilities in this regard are discussed below with reference to specific crystalline materials and gases.

#Herein the term nanosheet is used in a conventional sense to denote a layered structure that is essentially two-dimensional in character. The nanosheet is typically less than 10 nm in thickness and may extend in other directions in micron dimensions.