A novel method for producing boron nitride nanosheets via synergistic exfoliation with pure shear ball milling and ultrasonication

In this study, we propose a novel method to exfoliate hexagonal boron nitride (h-BN) powders to produce boron nitride nanosheets (BNNSs) by applying the synergistic exfoliation resulting from pure shear ball milling and ultrasonication. Pure shear ball milling is based on traditional ball milling, but uses a supplemental weight block as a vertical load on the milling balls. The effects of the vertical load on the average tangential force, average normal force, and the number of contacts among the milling balls were analyzed by discrete element method (DEM) simulation. The simulation results showed that applying a vertical load to the milling balls could alter their pattern of motion. It also increased their average tangential force and number of contacts, resulting in higher exfoliation and less impact action on the bulk h-BN powders. BNNSs were respectively produced by using the proposed method, traditional ball milling combined with ultrasonication method, and the ultrasonication method. Analyses by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) have revealed that the proposed method can produce BNNSs having larger lateral sizes with higher productivity, as compared to the other two methods. The proposed method is also expected to be applicable in the production of other layered two-dimensional (2D) materials.