Structural transformation of selenate ettringite: A hint for exfoliation chemistry

Exfoliation of layered materials has attracted tremendous interest since nanomaterials have become practically applied in many disciplines. In this study, the structural transformation of packed columnar selenate ettringite into nanoscale particles has been investigated. The structural transformation of ettringite has been evidenced based on the results of X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), and extended X-ray adsorption fine structure (EXAFS). The structural transformation is caused by the electrostatic repulsion between guest sulfate ions and selenate. However, the atomic arrangement of columnar parts of selenate ettringite is still maintained. In addition, a similar phenomenon is more noticeably observed when it is soaked in ethanol. This suggests that this columnar material has the potential to be exfoliated into a single nanoscale column by reactions with polar solvents. Finally, a stable colloidal solution formed when selenate ettringite was soaked in butanol. This is because the surface of the columnar parts in ettringite is surrounded by structural water molecules that can interact with OH groups of strongly polar solvent molecules to form hydrogen bonds that can directly exfoliate selenate ettringite and convert to nanoparticles. It is clear that ettringite could be directly exfoliated to nanoparticles in polar organic solvents, which has potential utility for wide applications.