Scalable exfoliation for large-size boron nitride nanosheets by low temperature thermal expansion-assisted ultrasonic exfoliation

Hexagonal boron nitride nanosheets (BNNSs) hold great potential in many applications due to their intriguing properties. However, the high-yield preparation of large-size BNNSs still remains a key challenge. Herein, we report a scalable exfoliation process, named as 'low temperature thermal expansion-assisted ultrasonic exfoliation', to prepare BNNSs. This method firstly utilizes hydrogen induced low temperature thermal reduction of hydroxyl-functionalized bulk hexagonal boron nitride (BN-OH) to weaken interlayer interaction between adjacent layers, and then employs a brief sonication to completely exfoliate BNNSs from their bulk materials. Few-layer and large-size BNNSs with a high yield of 26% are successfully prepared by this method. Moreover, the large-area BNNSs can effectively enhance the thermal conductivity of thermoplastic polyurethane elastomer on account of the decrease of interfacial thermal resistance. Low temperature thermal expansion-assisted ultrasonic exfoliation can thus provide an efficient approach to scalable fabrication of high-quality BNNSs. Furthermore, this method is promising for the high-yield production of other nanosheets.