Rockenberger, Scher and Alivisatos [57] have described the use of cupferron
complexes as precursors to prepare transition metal oxide nanoparticles. Cupferron (N-phenyl, N-nitroso hydroxylamine) forms bidentate, univalent complexes
with a number of different transition metals ions. These complexes easily decompose to give the oxide. The authors demonstrated the preparation of g-Fe 2 O 3 , Cu 2 O
and Mn 3 O 4 nanoparticles prepared by injecting octylamine solutions of the corresponding cupferron precursors into refluxing trioctylamine. Size is controlled by
controlling the temperature of the reaction. The particles so prepared form stable
solutions in solvents such as toluene, from which they can be reprecipitated by
the addition of methanol. This work is quite seminal in its generality, and particularly in the manner it which it suggests the search for suitable precursors for the
preparation of oxide nanoparticles. Most importantly, it suggests thermolysis as an
alternative to hydrolysis which, as pointed out earlier, is simply not viable for a
number of metal oxides.
An important contribution to the surface chemistry of metal oxide nanoparticles
has been made by Rotello and coworkers [58] who have prepared g-Fe 2 O 3 nanoparticles by the cupferron decomposition method, and compared the relative efficacies of different long chain surfactants as capping agents. The most stabilizing
capping agent (as monitored by ease of redissolution and stability in solution) was
obtained by using a two-tailed surfactant (with 12-carbon tails) with the polar part
comprising a 1,3-diol.
The thermolysis of Fe(III) hydroxide caprylates in boiling tetralin under argon
flow gives g-Fe 2 O 4 nanoparticles [59]. The surfaces of the nanoparticles could be
modified by exchanging the capping caprylate groups with betaine, among other
species [60]. Betaine-capped g-Fe 2 O 3 nanoparticles are reported to have high solubility in water. Using a combination of hydrolysis and oxidation, O’Brien, Brus and
Murray [61] have shown that the treatment of a complex alkoxide containing Ba
2þ
and Ti
4þ , BaTi(O 2 CC 7 H 15 )[OCH(CH 3 ) 2 ] 5 , an agent for the MOCVD growth of
BaTiO 3 , can be decomposed in diphenyl ether at 140
C, in the presence of oleic
acid as a capping agent, to give nanocrystalline, cubic BaTiO 3 [Figure 5.3]. After
cooling to 100
C, 30% H 2 O 2 is added, and crystallization is induced over a 48 h
period. Changing the ratio of capping agent to water, and the amount of peroxide
added, permits the size of the particles to be varied. This is perhaps the only report
of soluble perovskite oxide nanoparticles and, once again, is a route of great generality and interest. The authors also report using such routes to prepare PbTiO 3
and TiO 2 nanoparticles.
5.3.4
Metathesis
In a metathetic reaction, two compounds AB and CD, exchange species to give two
new compounds AC and BD. Such routes have been explored in the preparation of
nanoparticles. Arnal et al. [62] have reported two non-hydrolytic routes to sol–gel
metal oxides, particularly of titanium. The first route involves the reaction of a
metal halide with a metal alkoxide:
5.3 Routes for the Preparation of Isolated Oxide Nanoparticles 103
complexes as precursors to prepare transition metal oxide nanoparticles. Cupferron (N-phenyl, N-nitroso hydroxylamine) forms bidentate, univalent complexes
with a number of different transition metals ions. These complexes easily decompose to give the oxide. The authors demonstrated the preparation of g-Fe 2 O 3 , Cu 2 O
and Mn 3 O 4 nanoparticles prepared by injecting octylamine solutions of the corresponding cupferron precursors into refluxing trioctylamine. Size is controlled by
controlling the temperature of the reaction. The particles so prepared form stable
solutions in solvents such as toluene, from which they can be reprecipitated by
the addition of methanol. This work is quite seminal in its generality, and particularly in the manner it which it suggests the search for suitable precursors for the
preparation of oxide nanoparticles. Most importantly, it suggests thermolysis as an
alternative to hydrolysis which, as pointed out earlier, is simply not viable for a
number of metal oxides.
An important contribution to the surface chemistry of metal oxide nanoparticles
has been made by Rotello and coworkers [58] who have prepared g-Fe 2 O 3 nanoparticles by the cupferron decomposition method, and compared the relative efficacies of different long chain surfactants as capping agents. The most stabilizing
capping agent (as monitored by ease of redissolution and stability in solution) was
obtained by using a two-tailed surfactant (with 12-carbon tails) with the polar part
comprising a 1,3-diol.
The thermolysis of Fe(III) hydroxide caprylates in boiling tetralin under argon
flow gives g-Fe 2 O 4 nanoparticles [59]. The surfaces of the nanoparticles could be
modified by exchanging the capping caprylate groups with betaine, among other
species [60]. Betaine-capped g-Fe 2 O 3 nanoparticles are reported to have high solubility in water. Using a combination of hydrolysis and oxidation, O’Brien, Brus and
Murray [61] have shown that the treatment of a complex alkoxide containing Ba
2þ
and Ti
4þ , BaTi(O 2 CC 7 H 15 )[OCH(CH 3 ) 2 ] 5 , an agent for the MOCVD growth of
BaTiO 3 , can be decomposed in diphenyl ether at 140
C, in the presence of oleic
acid as a capping agent, to give nanocrystalline, cubic BaTiO 3 [Figure 5.3]. After
cooling to 100
C, 30% H 2 O 2 is added, and crystallization is induced over a 48 h
period. Changing the ratio of capping agent to water, and the amount of peroxide
added, permits the size of the particles to be varied. This is perhaps the only report
of soluble perovskite oxide nanoparticles and, once again, is a route of great generality and interest. The authors also report using such routes to prepare PbTiO 3
and TiO 2 nanoparticles.
5.3.4
Metathesis
In a metathetic reaction, two compounds AB and CD, exchange species to give two
new compounds AC and BD. Such routes have been explored in the preparation of
nanoparticles. Arnal et al. [62] have reported two non-hydrolytic routes to sol–gel
metal oxides, particularly of titanium. The first route involves the reaction of a
metal halide with a metal alkoxide:
5.3 Routes for the Preparation of Isolated Oxide Nanoparticles 103