The in-situ structural characterization of layered double hydroxide materials in catalytic and biological applications

Abstract

The overall aim of this PhD research is to understand the physical behaviours of layered double hydroxide (LDH) nanomaterials in applied environments. Two aspects of LDH-based applications were studied. Firstly, the thermal evolution of LDH nanomaterials were investigated using high-end (scanning) transmission electron microscopy ((S)TEM). The LDH nanomaterials underwent morphological, crystallographic and spectroscopic changes during thermal decomposition. The Ni-Fe LDHs were observed to evolve into an array of mixed metal oxides and spinel phases, shown by high resolution TEM (HRTEM), energy filtered TEM (EFTEM) and electron energy loss spectroscopy (EELS). In particular, in-situ TEM revealed the real-time processes of thermal decompositions where a nucleation and growth of an array of Nickel-based particles was observed. This NiO array was found to be embedded throughout a NiFe2O4 matrix. Similar behaviours were also seen ex-situ where STEM-EELS highlighted a segregation of Ni and Fe species upon ex-situ thermal decompositions of Ni-Fe LDH nanomaterials. Secondly, Mg-Al LDH properties were examined as they interacted with DNA based biomolecules and transfected by biological cells. It was found that the Mg-Al LDHs were successfully up-taken by mesenchymal stem cells and A549 cells. After 72 hours, the particles were observed to reside in the cytoplasm regions. Electron diffraction related studies indicated that the LDH particles retained their crystallographic nature. This was corroborated by EFTEM and STEM-EELS studies of the oxygen K edge, whilst maintaining their structural integrity. The associated findings have vital influences on the future LDH applications in the areas of catalysis, flame retardants and drug delivery. Notwithstanding these research areas, our results impact future applications as a whole, where the versatile LDH nanomaterials should be considered as prime candidates across nanotechnology.