Abstract
A comprehensive nanoscale understanding of layered double hydroxide (LDH) thermal evolution is critical for their current and future applications as catalysts, flame retardants and oxygen evolution performers. In this report, we applied in situ transmission electron microscopy (TEM) to extensively characterise the thermal progressions of nickel-iron containing (Ni-Fe) LDH nanomaterials. The combinative approach of TEM and selected area electron diffraction (SAED) yielded both a morphological and crystallographic understanding of such processes. As the Ni-Fe LDH nanomaterials are heated in situ, an amorphization occurred at 250 °C, followed by a transition to a heterogeneous structure of NiO particles embedded throughout a NiFe2O4 matrix at 850 °C, confirmed by high-resolution TEM and scanning TEM. Further electron microscopy characterisation methodologies of energy-filtered TEM were utilised to directly observe these mechanistic behaviours in real time, showing an evolution and nucleation to an array of spherical NiO nanoparticles on the platelet surfaces. The versatility of this characterisation approach was verified by the analogous behaviours of Ni-Fe LDH materials heated ex situ as well as parallel in situ TEM and SAED comparisons to that of an akin magnesium-aluminium containing (Mg-Al) LDH structure. The in situ TEM work hereby discussed allows for a state-of-the-art understanding of the Ni-Fe material thermal evolution. This is an important first, which reveals pivotal information, especially when considering LDH applications as catalysts and flame retardants.
Highlights
In recent years, two-dimensional (2D) nanomaterials have been described as strongholds across the fields of nanotechnology with extensive applications in electronics, catalysis, drug delivery, photonics or magnetics.[1]
The application of Ni-Fe layered double hydroxide (LDH) in these fields is largely owed to their inherent material properties such as simplistic methods of fabrication, low cost, large specific surface areas, greater active sites and ability to interact with various catalytic supports
The (XRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA).[8,27,33,34,35]. In addition to these characteras-synthesised LDH samples were subjected to identical heating ramp conditions both in ex situ and in situ experimental set-ups isation techniques, pre-mortem and post-mortem electron (Figure S2)
Summary
Two-dimensional (2D) nanomaterials have been described as strongholds across the fields of nanotechnology with extensive applications in electronics, catalysis, drug delivery, photonics or magnetics.[1]. In situ and ex situ heating TEM experiments were comparatively carried out in parallel to fully understand the development of LDH research, the majority of these works have largely relied on thermally induced calcination, as well as the various crystalmacroscopic characterisation techniques such as X-ray diffraction lographic transitions occurring before that For this purpose, the (XRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA).[8,27,33,34,35] In addition to these characteras-synthesised LDH samples were subjected to identical heating ramp conditions both in ex situ and in situ experimental set-ups isation techniques, pre-mortem and post-mortem electron (Figure S2). We defined hexagonal morphology with a lateral dimension on the report on the application of state-of-the-art in situ transmission order of microns This starting material was found to have an LDH electron microscopy to reveal the processes by which LDHs crystallographic strÀucturÁe,À witÁh the associated SAED pattern thermally decompose and to characterise the stages at which revealing the (101), 011 , 112 and (110) crystallographic planes these morphological and crystallographic alterations occur. Images (Fig. 2a, b) indicates a surface alteration at this temperature, possibly as a consequence of the additional loss of
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