Three-Dimensional Architectures of (NH4,Na)3AlF6 Solid Solution: Synthesis, Shape Evolution, and Growth Mechanism

Abstract

A series of novel frameworks of (NH4,Na)3AlF6 microcrystals including octahedron, hexapod, hole octahedron, flower, and open truncated octahedron have been prepared in solution phase via manipulating synthetic parameters. The obtained samples were characterized by X-ray powder diffraction (XRD), X-ray fluorescence (XRF), magic angle spinning nuclear magnetic resonance (MAS NMR), field emission scanning electron microscopy (FESEM), selected area electron diffraction (SAED), and transmission electron microscopy (TEM). The effects of pH, reactant molar ratio, temperature, and reaction time on the self-assembly of (NH4,Na)3AlF6 microcrystals were systematically investigated. On the basis of our experimental results, a plausible microcrystal-stack-based growth mechanism is proposed for the formation of the various hierarchical architectures, and EDTA-2Na only acts as both a Na+ source and a chelating reagent in the synthesis process. Such a microcrystal-stack process may also provide a basis for the creation of intracrystal porosity and crystal self-amplification.