Iron-Based Magnetic Nanoparticles for Removal of Heavy Metals from Electroplating and Metal-Finishing Wastewater - Nanotechnologies for Water Environment Applications - page 233

of 7.5% and 13.1% were investigated using the TEM technique, and the images are
shown in Figure 9.11. Particles surface morphology analysis revealed the agglomeration
of many ultrafine particles. Figure 9.11a shows the pure circular -Fe 2 O 3 nanoparticles
with dimension of around 15 nm. Figure 9.11b shows a small number of circular
particles with a length of 100 nm and a width of 10 nm, besides the circular -Fe 2 O 3 .
Figure 9.11c shows an increased amount of acicular particles, with the same dimension
as those shown in Figure 9.11b. It is observed that the needle-shaped particles emerged
with doping aluminum and their number increased with an increase in dosage of Al-
doping. Incorporation of Al resulted in preferential crystal growth along the [100]
direction (i.e., crystal width) producing irregular shaped, platy particles of 500 nm in
size, at the expense of crystal thickness.
Figure 9.12 gives the XRD patterns of -Fe 2 O 3 particles in the presence and
absence of Al-dopant. The XRD peaks on plasma-torched powders revealed that most of
the precipitate was transformed into nanocrystalline material. All major peaks were
indexed to the standard pattern for -Fe 2 O 3 . It is found that the peaks of Al-doped -
Fe 2 O 3 particles still remained the same ratio and width as those of pure -Fe 2 O 3 , with
only a little shifting of positions to the left side. A shift only occurs if the replacing
cation is sufficiently different in size from that of Fe III ion (Schwertmann and Cornell,
2000). For this case, such a replacement due to size difference between Fe (r = 0.064nm)
and Al (r = 0.053nm) inevitably results in the shift of XRD peaks. A definite proof of
structural incorporation can, therefore, be deduced from this shift in the position of the
XRD peaks. This phenomenon also demonstrated that adding a certain amount of
aluminum into -Fe 2 O 3 crystal would not change the structure of the pure -Fe 2 O 3 .
Figure 9.12 XRD patterns of -Fe 2 O 3 with or without Al-doping.