Facile and scalable preparation of ultra-large boron nitride nanosheets and their use for highly thermally conductive polymer composites

Due to their excellent physical and chemical properties, boron nitride nanosheets (BNNSs) have shown great application potential in many fields. However, the difficulty in scalable preparation of large-size BNNSs is still the current factor that limits this. Herein, a simple yet efficient microwave-assisted chemical exfoliation strategy is proposed to realize scalable preparation of BNNSs by using perchloric acid as the edge modifier and intercalation agent of h-BN. The as-obtained BNNSs behave a thin-layered structure (average thickness of 3.9 nm) with a high yield of ∼16%. Noteworthy, the size of BNNSs is maintained to the greatest extent so as to realize the preparation of BNNSs with ultra-large size (up to 7.1 µm), which is the largest so far obtained for the top-down exfoliated BNNSs. Benefiting from the large size, it can significantly improve the thermal diffusion coefficient and the thermal conductivity of polyvinyl alcohol by 51 and 62 times respectively, both showing a higher value than the one previously reported. This demonstrates that the prepared BNNSs have great promise in enhancing the thermal conductivity of polymer materials.