Layered Double Hydroxides and the Environment: An Overview - Advanced Materials for Agriculture, Food and Environmental Safety - page 12

between the brucite-like sheets. Besides this, information about the type
of bonds formed by the anions and about their orientations can also be
obtained. h e infrared region is the region found in the wave number
range 1.3×10 4 - 3.3×10 1 in the electromagnetic spectrum [82].
h e FTIR is used to investigate the structural bonding and chemical
properties of compounds [83]. On absorbing radiation by the molecule,
the bond can stretch/vibrate or bend [84]. Each molecule absorbs a spe-
cii c IR radiation depending on the type of functional group present. h e
resultant peaks in the IR spectra are called the “molecular i nger print.”
h erefore, each functional group has its own frequency and this is useful
for revealing the presence or absence of these groups from the spectra.
Some specii c characteristic peaks of LDHs are: peaks at 3500-4000 cm -1
assigned as -OH absorption and Interlayer CO 3 2- (LDH-CO 3 ) [85, 86];
peaks at <1000 cm -1 assigned as the inorganic lattice vibrations of M-O and
M-OH modes [86]; peaks at 1560-1400 cm -1 due to intercalated anionic
species (e.g., Carboxylate-LDH) [80] and due to strong asymmetric and
symmetric stretching bonds, and; peaks around 1360 cm -1 which can be
assigned as carbonate impurity and nitrates [86].
1.5.3 h ermogravimetric Analysis and Dif erential
h ermal Analysis
h ermogravimetric analysis (TGA) is used to measure changes in the mass
of LDH and estimate the content of water and anion molecule, while dif-
frential thermal analysis (DTA) can be used to study thermal properties and
phase changes that can occur upon heating the LDH/ LDH hybrids. Most
thermal events correspond to water/anions removal from interlayer spaces.
1.5.4 Other Techniques
Other techniques include scanning electron microscopy (SEM), transmis-
sion electron microscopy (TEM), dif erential scanning calorimetry (DSC),
X-ray l uorescence spectroscopy (XRF), Raman spectroscopy and nuclear
magnetic resonance (NMR).
Scanning electron microscopy is used to study the surface topography
of LDH intercalates by which particle morphology, porosity and phase
composition within the material can be revealed. Both SEM and TEM pro-
vide general pictures of textural and crystal morphologies of LDHs. A hex-
agonal platelet morphology is usually shown by LDH [36, 87].
Both DSC and TGA are also used to check the chemical and physical
properties of a material corresponding to temperature changes. It is used