Superacid assisted high-throughput production and solution-processing of pristine two-dimensional materials

Abstract

Pristine two-dimensional (2D) materials have a multitude of interesting properties, promising a broad spectrum of applications. However, their poor affinity for common solvents and tendency to aggregate impede their effective exfoliation and solution-processing into various structures, such as fibers and membranes, thus limiting their practical use. We report a high-efficiency method for producing pristine 2D nanosheets by direct high-speed shearing exfoliation in trifluoromethanesulfonic acid (TfOH). Typically, this method produces hexagonal boron nitride nanosheets (BNNSs) with an unprecedented throughput of 38.8 mg mL^-1h⁻¹. The effective exfoliation is attributed to the strong binding affinity, large dipole moment and steric repulsion of TfOH, which collectively introduce layer edge distortion in hexagonal boron nitride (hBN), facilitating its exfoliation. The mechanical exfoliation and reversible edge interaction introduce no additional functional groups to the exfoliated BNNSs. The resulting pristine BNNS exhibit remarkable stability in TfOH solutions at ultrahigh concentrations of 200 mg mL⁻¹ for over 28 days. The viscosity of the highly concentrated BNNS/TfOH dispersion can be adjusted, enabling techniques to produce BNNS-based spheres, fibers, and membranes with high thermal conductivity and mechanical strength, suitable for advanced thermal management applications. Room temperature processed BNNS-based spheres exhibit superior thermal conductivity compared to high temperature processed commercially available hBN or Al₂O₃ spheres. Moreover, TfOH can also be used to assist the efficient production and solution-processing of other 2D nanosheets, including graphene, molybdenum disulfide and tungsten disulfide, enabling the fabrication of high-quality bulk assemblies.