Solubility of MoS2 and Graphite in Molten Salt: Flowers, Faceted Crystals, or Exfoliation?

2D materials are of interest in various applications such as energy conversion, storage, and sensing. These materials are prepared by bottom-up or top-down methods that are difficult to control and suffer from low yield. Synthesis in molten salt is suggested as an alternative in which the balance between exfoliation and solubility is explored. It is demonstrated that when a pellet of 2D material is insoluble in molten salt (graphite in any salt), it is exfoliated. For low solubility (MoS2 in NaCl/KCl), the 2D material nucleates and grows into a small flowerlike structure composed of thin MoS2 sheets through Ostwald ripening. For high solubility in the molten salt (MoS2 in CsCl), it forms larger flowers. Herein, the molten salt treatment of high and low surface area MoS2 (micron-size particles and a single large pellet, respectively) is compared. The particles yielded facet MoS2 crystals through dissolution-nucleation-recrystallization process and the pellet yielded flowers. Herein, methods for synthesizing 2D materials with controllable size and shape are promoted by simple molten salt treatment that opens an avenue to the development of soluble (MoS2) and non-soluble (graphite) materials with different morphologies in a simple and affordable way.