Nano-hexagonal boron nitride sheet preparation by molten salt method

Abstract: [Background] Hexagonal boron nitride has a lamellar structure composed of six-membered rings similar to that of graphene, thus presenting excellent mechanical properties and thermal conductivity, and has attracted widespread attention in many applications. [Purpose] Based on the high energy consumption problem of hexagonal boron nitride preparation process, this paper aims to propose a greener and lower energy consumption preparation process. [Methods] In this work, the molten salt media method was used as a preparation process method. The method used KCl-NaCl as the molten salt system, melamine (C3N6H6) and boric acid (H3BO3) as the reactants, and nitrogen (N2) was introduced as the reaction atmosphere. In this study, the effect of different conditions on the preparation of hexagonal boron nitride products was systematically investigated by varying the mass ratio of the molten salt to the reactants, the nitrogen-boron molar ratio in the reactants, the holding temperature and the holding time. The optimum preparation conditions were derived from the characterization and analysis of various obtained samples. [Results] Under the systematic study in this work, a mass ratio of molten salt to reactants of 2:1, a nitrogen-to-boron molar ratio of 1:2, and a holding time of 10 hours at 1000 °C are found to be the optimum preparation conditions. Hexagonal boron nitride nanosheets with an average size of about 50 nm size can be prepared under this condition. It indicates that hexagonal boron nitride nanosheets with controllable particle size, consistent morphology and good crystallization can be prepared under the optimal process conditions. [Conclusions] The present work provides a new way to synthesize hexagonal boron nitride nanosheets in a green and low-carbon manner.