Synthesis of Nanoparticles and One-Dimensional Nanomaterials - Nanotechnologies for Water Environment Applications - page 17

Al 2 O 3 nanoparticles by using AlCl 3 ·6H 2 O and Al powder as raw materials. Aluminum
chloride hexahydrate may be hydrolyzed to produce the sol:

AlCl 3 + 3H 2 O Al(OH) 3 + 3HCl BBBBBB B B B BBBBBB (Eq.

2.5)

In addition, through the reaction between Al powder and HCl aluminum chloride and
hydrogen gas are produced:

2Al + 6HCl 22AlCl 3 + 3H 2 (Eq. 2.6)

Therefore, Al can be used as a source of AlCl 3 to produce the sol containing Al(OH) 3
nanoparticles. Finally, the hydroxides groups produced aggregate together to form the
gel. The obtained gel was dried and then ground and calcined in a furnace at different
temperatures. The gel calcined at 1100 °C resulted in the formation of crystalline -
Al 2 O 3 nanoparticles. It had a particle size distribution ranging from 32 to 100 nm after
heat treatment at 1100 °C. This material can be used as the catalyst supports and high
temperature applications.
2.2.2 Forced Hydrolysis

A forced hydrolysis method is a simple method that can be used to synthesize
uniformly-sized metal oxide nanoparticles based on a metal salt solution (Hu et al.,
1998). A forced hydrolysis method can also be used to reference the process or ability of
many hydrated metal ions, especially polyvalent metal cations, that readily deprotonate
in aqueous solutions at elevated temperatures. This characteristic can be used to
advantage in the preparation of colloidal particles from such materials. Since the
hydrolyzed products of these metal ions are intermediates used to precipitate
corresponding hydroxides, it is possible to prepare samples with a very narrow particle
size distribution simply by heating the metal salt solution (Blesa et al., 1985). At an
elevated temperature, the hydrolysis reaction should be faster and generate a
respectively larger number of nuclei. This in turn should lead to the formation of smaller
particles. In forced hydrolysis procedures, the pH and nature of the anions, solvents, and
precursors all play a dominant role in nanomaterial synthesis.
This principle was demonstrated by the formation of monodisperse silica spheres
by Stöber et al. (1968). The procedure for silica sphere fabrication is as follows (Stöber
et al., 1968):
Si(OR) 4 + (alcohol + NH 3 + H 2 O) 50 nm-2 m SiO 2 (Eq. 2.7)
Here, ammonia was reacted as a catalyst to form spherical silica particles. In basic
conditions, three-dimensional structures are formed by a condensation reaction, instead