6
8
Chemistry Letters Vol.37, No.1 (2008)
Hybrid of Polyaniline/Iron Oxide Nanoparticles:
Facile Preparation and Catalytic Application
ꢀ
Toru Amaya, Yumiko Nishina, Daisuke Saio, and Toshikazu Hirao
Department of Applied Chemistry, Graduate School of Engineering, Osaka University,
Yamada-oka, Suita, Osaka 565-0871
(Received September 12, 2007; CL-070999; E-mail: hirao@chem.eng.osaka-u.ac.jp)
The facile preparative method of iron oxide nanoparticles
1 and 2, respectively). TEM images for the sample prepared in
NMP exhibited the obscurely visible particles (Entry 3). The
nanoparticles were obtained after stirring in 2-pyrrolidone and
with polyaniline was developed by thermal reaction of
Fe(acac)3. The efficient catalytic activity was demonstrated in
the oxidative coupling of 2,6-di-t-butylphenol.
ꢁ
15
DMF for 6 h at ca. 150 C (Entries 4 and 5, respectively).
The TEM image of the particles prepared in DMF (Entry 5)
was shown in Figure 1. The particle size was distributed in the
range of diameter 3–9 nm (average diameter = 5.6 nm, standard
deviation ꢁ ¼ 1:1, number of counted particles = 212). The
particles were relatively dispersed well. EDX experiment
showed the presence of Fe. The observed nanoparticles were as-
signed to iron oxide judging from the reported thermal reaction
Hybrids of metal oxide nanoparticles and ꢀ-conjugated
polymers are expected to create a novel class of electrical device
materials and catalysts due to the characteristic properties as
electron mediators.1 Polyaniline (PANI) is one of the most
important ꢀ-conjugated compounds as documented well. Some
reports described the preparation and characterization of PANI/
1
3
of Fe(acac)3, although it was difficult to determine the oxida-
tion state, Fe O or Fe O . The reaction mechanism might be
2
metal oxide nanohybrids, such as PANI/TiO2 and PANI/Iron
3
3
4
2
3
oxide nanoparticles. On the other hand, we have studied the
synthesis of d,ꢀ-conjugated complexes of PANI and its deriva-
tives with various metal salts, such as Pd and Cu , and even
explained as reported reactions in Refs. 12 and 13. The charac-
teristic absorptions for polyaniline were observed in the IR
II
II
ꢂ1
ꢂ1
spectrum (1596 cm for the quinonediimine and 1490 cm
for the phenylenediamine). There were no peaks derived from
heterometals.4 Furthermore, PANI serves as a redox-active li-
,5
6
gand in the transition-metal-catalyzed oxidation reaction. Re-
cently, the synthesis of PANI/Pd nanoparticles based on tem-
Fe(acac) . The UV–vis spectrum showed the charge-transfer
3
(CT) absorption between the benzenoid and quinoid moieties
of PANI at around 600 nm. Reaction at a lower temperature
7
plate method and catalytic application were demonstrated.
ꢁ
The synthesis of PANI/iron oxide nanohybrids is considered
to permit useful catalysts and electrical materials. However,
the catalytic application including carbon–carbon bond forma-
tion has not been investigated with PANI/Iron oxide nanoparti-
cles, to our knowledge.
(100 C) did not give the nanoparticles (Entry 6). The TEM
images after stirring in DMF for 3 h did not show the sharply
visible particles (Entry 7), which suggests the reaction time is
too short to grow the particles. On the other hand, the aggregated
particles were observed after stirring in DMF for 24 h (Entry 8).
The catalytic activity of the thus-obtained nanoparticles was
investigated in the oxidative coupling of 2,6-di-t-butylphenol
Various methods to prepare iron oxide nanoparticles were
8
reported so far. The size and dispersity of the nanoparticles have
been focused on, and recently the size control below 10 nm has
been reported. Conventionally, they were prepared from an
aqueous solution of FeCl2 and FeCl3 with a surfactant under
Table 1. Synthesis of PANI/iron oxide nanoparticles
H
N
H
N
9
Fe(acac)3
+
N
N
the basic conditions. Some reports describe the decomposition
of Fe(acac)3 in the presence of alcohol, amine, or carboxylic acid
n
1
0
PANI (emeraldine base)
having a long alkyl group in an organic solvent. Metal carbon-
yl was thermally decomposed and oxidized to afford the iron ox-
ide nanoparticles.11 More recently, thermal reaction of Fe salts
without any additives was found to give the iron oxide nanopar-
thermal reaction
III
solvent, temperature, time
PANI/iron oxide
nanoparticles
Ar
1
2
ticles when 2-pyrrolidone was used as a solvent. Herein, we
report the facile preparation of small-sized and well-dispersed
iron oxide nanoparticles with PANI through thermal reaction
of Fe(acac)3 and their application to the oxidative coupling of
Temp Time Diameter
ꢁ
Entry Solv.
Dispersity
/
C
/h
/nm
1
2
3
4
5
6
7
8
THF
Dioxane
NMP
66
6
6
—
—
—
—
100
150
2,6-di-t-butylphenol.
Fe(acac)3 was employed as a single iron source. Thermal re-
6
Few visible particles
2-Pyrrolidone 150
6
3–12
3–9
—
Wella
Wella
—
action was carried out in the presence of PANI (the emeraldine
base purchased from Aldrich, MW = ca. 10000) under argon in
various solvents. After stirring for several hours, the reaction
mixture was diluted with water to form the precipitate. The sus-
pension was filtered through a membrane filter. The residue was
thoroughly washed with deionized water and dried. The obtained
solid was observed by TEM. Table 1 summarizes the results. The
use of THF and dioxane did not afford the nanoparticles (Entries
DMF
DMF
DMF
DMF
153
100
153
153
6
6
3
24
Few visible particles
—
Aggregatedb
a
The particles were relatively dispersed well (each particle is
b
almost independent in the TEM image). The particles were
aggregated together to form the >50 nm-sized particles.
Copyright Ó 2008 The Chemical Society of Japan