Microwave-assisted synthesis and characterization of hierarchically structured calcium fluoride

CaF2 with different morphologies and hierarchical structures was prepared under microwave-assisted condition by a simple hydrothermal route using CaCl2 and ionic liquid [BMIM]BF4 as initial reagents, respectively. It was found that both the precursor and pH values played an important role in the formation of CaF2 crystals with different morphologies. The results suggested that the CaF2 with cube and spherical structures was obtained at different pH values (4, 8, 11), while the CaF2 with dendrite shape was formed through an oriented self-assembly growth using (NH4)2HPO4 as a structure directing agent. Scanning electron microscope observation showed that the as-prepared CaF2 was of three-dimensional eight-horn-shaped dendritic structure. The influence of the pH values for the reaction solution and precursors has been discussed in detail. On the basis of the experimental results, possible growth mechanisms of the CaF2 microcrystals were proposed.