As a new type of two-dimensional nanomaterials, boron nitride nanosheets have excellent thermally conductive, electric insulating, mechanical properties and biocompatibility. It has gradually become a research focus, because of its extensive applications in composite reinforcement, thermally conductive composites, hydrogen storage, drug transport, catalytic carriers, quantum dots, etc. Boron nitride has four crystalline forms: hexagonal (h-BN), cubic (c-BN), rhombohedral (r-BN) and fiber mineral (w-BN). Among the four phases, h-BN is the most stable under standard conditions and is a sp2-hybridized 2D-layered insulator. However, the van der Waals force is stronger than that of graphite, which makes it difficult to peel. Till now, many methods for preparing boron nitride nanomaterials have been explored, such as micromechanical peeling, liquid phase peeling, chemical vapor deposition (CVD), and secondary epitaxial growth, which were referenced graphene preparation method. Although these methods have their own advantages and disadvantages, there are certain problems in large-scale stable production of BNNSs with relatively complete crystal structures and high stripping efficiency. How to prepare BNNSs with low cost, high efficiency and high quality is the key to its industrialization. Supercritical fluids have both the diffusive properties of gases and the ability to dissolve liquids. Since they were introduced into the preparation of graphene and have achieved some results, many researchers have also applied them to the preparation of BNNSs. At present, BNNSs with a thickness of 2- 6 nm can be prepared by using supercritical CO2 at a certain temperature and pressure, and the crystal form of BNNSs is the same as the original h-BN. The concentration of the obtained BNNSs suspension can be as high as 0.24 mg/mL. It can effectively improve its peeling efficiency after being assisted by means of shearing and ultrasound. Supercritical organic solvents include supercritical methanol and supercritical N, N-dimethylformamide, which can not only open the interlayer distance as an intercalating agent, but they can also be a good dispersant to prevent nanomaterials from agglomerating again. Supercritical organic solvents can greatly simplify the stripping process. 2 to 3 layers of BNNSs without obvious defects can be obtained after 15 minutes, which has about 10% yield. In this review, we first describe the methods, principles, research status, and characterization methods of preparing BNNSs by supercritical fluid, and discusses various methods and advantages and disadvantages of improving stripping efficiency. The equipment for preparing boron nitride nanosheets by supercritical fluid is simple, the conditions are easy to achieve, and the product quality is high, which provides new ideas for the industrial production of boron nitride nanosheets. © 2021, Materials Review Magazine. All right reserved.
