Nanostructured Materials Produced by Mixing and Restacking of Delaminated Layered Double Hydroxides

Active restacking from mixtures of colloidal dispersions of delaminated layered double hydroxides (LDH) having different chemical compositions was investigated as a route for the formation of new nanostructured materials. Three nitrate-based layered double hydroxides (MgAl-NO3, MgGa-NO3, and CoAl-NO3) were delaminated in formamide. The colloidal dispersions were then mixed two-by-two and subsequently restacked into three new materials: MgAl-MgGa-CO3-res, MgAl-CoAl-CO3-res, and CoAl-MgGa-CO3-res. Various X-ray powder diffraction (XRPD) techniques were combined with high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and energy dispersive X-ray spectroscopy (EDXS) to investigate the potential nanostructuring of the new materials. X-ray diffraction experiments showed that MgAl-MgGa-CO3-res is a two-phase mixture with one MgAl-CO3 based phase and one MgGa-CO3 based phase, whereas the powder patterns of MgAl-CoAl-CO3-res and CoAl-MgGa-CO3-res indicated that the samples are single phases. HAADF-STEM and EDXS studies showed that the nanosheets of the delaminated CoAl-NO3 and MgGa-NO3 were mixed down to the nanometer scale in the restacked CoAl-MgGa-CO3-res, supporting that the sample is a single phase. In situ high temperature XRPD experiments confirmed that CoAl-MgGa-CO3-res is not a simple mixture of two segregated CoAl-CO3 and MgGa-CO3 phases but a new nanostructured material with LDH-type structure consisting of two chemically different brucite-type layers. Furthermore, the in situ XRPD experiments showed that the thermal development of the restacked CoAl-MaGa-CO3-res and a coprecipitated and anion-exchanged MgCoAlGa-CO3 is different.