Preparation of Two Dimensional Atomic Crystals BN, WS2, and MoS2 by Supercritical CO2 Assisted with Ultrasound

A facile and general approach was developed to exfoliate layer materials to produce two-dimensional atomic crystals. A single and few layers of BN, MoS2, and WS2 were obtained via directly exfoliating their powder materials using supercritical CO2 assisted with ultrasound. The effects of supercritical CO2 coupled with ultrasound play a key role in the exfoliation process. The layer numbers and sizes of the BN, MoS2, and WS2 can be easily controlled by adjusting the power and the time of ultrasonication. The AFM images suggest single-layered BN, MoS2, and WS2 were produced, respectively. Their lateral sizes are about 0.5-2 mu m, and almost 90% of the BN sheets are less than five layers. The electric diffraction patterns demonstrate that the crystallinities of the produced samples remained the same as that of the raw material during the exfoliating process. This novel technique is cost-effective and scalable, and can be widely used in the production of two-dimensional atomic crystals with high quality.