Geoscience Reference
In-Depth Information
and so on). There is a huge opportunity for discovering hybrid analogues of classi-
cal oxide systems that exhibit a wide range of physical properties. Future targets
should include metallic hybrids (analogues of conducting polymers), lasers, and
even superconductors.
10.7.1 Organic
Inorganic Hybrid Nanoparticles
Although the study of hybrid nanoparticles is considered to be a recent develop-
ment, the literature survey shows that the approach to process organic
inorganic
materials began during the 1970s. Several chemical routes were employed to
prepare such hybrid nanoparticles and disperse them in the organic solvents.
Silane-coupling agents have been in common use for decades providing enhanced
adhesion between a variety of inorganic and organic agents. The general formula
of these organosilane coupling agents is R
n
SiX
(4
2
n)
, having dual functionality. The
majority of silane-coupling agents contain a hydrolyzable group (X), typically
methoxy or ethoxy which readily reacts with a proton to give methanol or ethanol
as by-products of the coupling. Metal oxide has hydroxyl groups which provide the
necessary proton for the coupling reaction. The “R” group is a nonhydrolyzable
organic group designed to provide a hydrophobicity nature for the surface of metal
oxide nanoparticles. In this case, as shown in
Figure 10.51
, by dehydration reaction
between the silane-coupling agent and OH groups of metal oxide, stable bonds of
M
C will be formed, resulting in the surface modification and changing
the surface property of
O
Si
the metal oxides from hydrophilic to hydrophobic
[229
232]
. The greatest disadvantage of this route is the presence of Si shell in the
structure of hybrid organic
inorganic metal oxide particles introducing significant
changes in the original properties of these metal oxides and limiting their applica-
tions. For example, silane is very sensitive to UV radiation, and this type of hybrid
metal oxides, like ZnO, cannot be used for such applications as sun block. Further,
the silica shell around the metal oxide significantly increases with the size of the
modified particles. Thus, by considering such an ex situ surface modification with
functional groups and a silane-coupling agent, the problem of surface modification
Figure 10.51 Schematic
representation of the modified
metal oxide particles with silane
coupling agent.
RSi(OR)
n
-
-
-
MO
OH
MO
MO
OSi
C
Stable
Silane coupling
Silica
shell
OH
O
O
H
H
(R'O)
3
SiR
MO
x
O
O
H
H
OH
Metal oxide
nanoparticle
Modified metal oxide
nanoparticle
