Surfactant-free hydrothermal synthesis of sub-10 nm γ-Fe 2O3-polymer porous composites with high catalytic activity for reduction of nitroarenes

Article abstract of DOI:10.1039/c3cc44523b

Porous γ-Fe₂O₃-polymer composites were synthesized by a novel one-pot surfactant-free hydrothermal approach. The γ-Fe₂O₃-polymer composites consisting of 3.5 nm γ-Fe₂O₃ nanoparticles and porous polymers exhibited high catalytic activity and recycling performance in the reduction of nitroarenes. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3cc44523b

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Surfactant-free hydrothermal synthesis of sub-10 nm
c-Fe O –polymer porous composites with high
catalytic activity for reduction of nitroarenes†
2
3
Cite this: Chem. Commun., 2013,
4
9, 10088
Received 17th June 2013,
Accepted 5th September 2013
ab
b
b
b
b
Xianmo Gu, Zhenhua Sun,* Shuchang Wu, Wei Qi, Haihua Wang,
a
b
Xianzhu Xu* and Dangsheng Su*
DOI: 10.1039/c3cc44523b
www.rsc.org/chemcomm
Porous c-Fe
one-pot surfactant-free hydrothermal approach. The c-Fe
composites consisting of 3.5 nm c-Fe nanoparticles and porous in many applications ranging from catalysis, light emitting diodes,
polymers exhibited high catalytic activity and recycling perfor- and solar energy cells.
2
O
3
–polymer composites were synthesized by a novel non-toxic system under mild conditions. Meanwhile, the metal oxide–
2 3
O –polymer polymer composites have recently been receiving increasing attention
2 3
O
10–12
The polymer not only served as a carrier
mance in the reduction of nitroarenes.
of metal oxide particles, but also controlled the structures and
morphology of metal oxide particles. So far, various approaches have
Iron oxide nanoparticles have attracted considerable interest because been reported for the synthesis of metal oxide–polymer composites,
of their potential for use in a wide range of applications, for example, but there are only a few methods reported for the one-pot synthesis
ferrofluids, biomedical imaging, drug and gene delivery, energy of sub-10 nm metal oxide nanoparticle–polymer composites in an
1–4
storage devices, wastewater cleaning, and catalysis. The physical environmentally friendly system. Herein, we report a one-pot
and chemical properties of iron oxides are largely dependent on their surfactant-free hydrothermal route to synthesize sub-10 nm
5
structures, morphologies, and sizes. To date, some studies have g-Fe
2
O
3
–polymer porous composites by the thermal decomposition of
indicated that iron oxide nanoparticles of small size have excellent iron(III) acetylacetonate followed by the polymerization with formalde-
6
catalytic performance due to their large specific surface area. There- hyde under the alkaline conditions. Compared with previous reports,
fore, synthesis of sub-10 nm iron oxide nanoparticles with controllable this method has the advantages of facileness, non-toxic and eco-
structure and size has been developed in recent years.
2 3 2 3
nomical. More importantly, g-Fe O in the g-Fe O –polymer composites
Various wet chemical processes have been used to synthesize was sub-10 nm in size and exhibited excellent catalytic activity and
maghemite nanoparticles including precipitation, thermolysis by recycling performance in the reduction of nitrobenzene to aniline.
7–9
organic metallic composition and carbonyl composition. Alivisatos
et al. have successfully synthesized moderately monodispersed g-Fe
The g-Fe O –polymer composites were obtained by the thermal
2 3
decomposition of iron(III) acetylacetonate and formaldehyde under
2
O
3
nanocrystals of 6–7 nm diameters by injecting solutions of cupferron the basic conditions at 160 1C. The detailed experimental process is
7
complexes into long-chain amines at 300 1C. During the process, described in the ESI.† The reaction process is summarized in
high temperature and toxic organic solvents were used, which were Scheme 1. Iron(III) acetylacetonate was first decomposed into an
detrimental for energy conservation and environmental protection. acetylacetonate anion and iron hydroxide under alkaline conditions
Cui et al. have reported a facile solvothermal synthesis of near when the temperature of the reaction system was raised to 160 1C.
8
monodispersed Fe O nanoparticles on a gram scale. Although this Then, the acetylacetonate anion reacted with formaldehyde to
3
4
method was carried out at a low temperature, the synthesis needed a produce polymers. Meanwhile, iron hydroxide was converted into
surfactant as a stabilizer. Therefore, it is very necessary to develop a g-Fe nanoparticles. Finally, g-Fe –polymer composites were
2
O
3
2 3
O
facile method to synthesize sub-10 nm iron oxide nanoparticles in the
a
State Key Laboratory of Urban Water Resource and Environment, Harbin Institute
of Technology, Harbin 150090, P. R. China. E-mail: xuxianzhu@hit.edu.cn;
Fax: +86 451 86403625; Tel: +86 451 86403715
b
Shenyang National Laboratory for Material Science, Institute of Metal Research,
Chinese Academy of Sciences, 110016 Shenyang, P. R. China.
E-mail: zhsun@imr.ac.cn, dangsheng@fhi-berlin.mpg.de; Fax: +86 24 83970019;
Tel: +86 24 83978238
†
Electronic supplementary information (ESI) available: Experimental details,
characterization, catalytic measurement, a table of synthetic parameters and
catalytic activity, XRD, TEM and SEM images. See DOI: 10.1039/c3cc44523b
2 3
Scheme 1 The formation process of the g-Fe O –polymer composites.
1
0088 Chem. Commun., 2013, 49, 10088--10090
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Fig. 2 TG-DSC curves (a), FT-IR spectrum (b), XPS spectrum (c) and N
isotherm (d) of the g-Fe –polymer composites.
2
adsorption
2 3
O
the g-Fe O –polymer composites (Fig. S2, ESI†) displayed doublet
2
3
À1
peaks with an isomer shift of 0.34 mm s and quadrupolar splitting
2 3
Fig. 1 TEM (a and b), HAADF-STEM (c) and HRTEM (d) images of the g-Fe O –
À1
14
of 0.68 mm s , which corresponded to g-Fe
TGA–DSC curves of g-Fe –polymer composites indicated
possible polymer content and the phase transformation of g-Fe
at increasing temperature under an air atmosphere (Fig. 2a). The
formed after 4 hours. It was important to emphasize that the relatively large mass loss from 160 to 370 1C was about B20.9%,
formation of polymers and g-Fe nanoparticles occurred nearly which is attributed to the combustion of the polymer, and there is
simultaneously. Therefore, g-Fe O nanoparticles were uniformly a large exothermic peak in the DSC curves, corresponding to
2 3
O .
polymer composites. Insets in (b) and (d) show the size distribution and the SAED
pattern of g-Fe nanoparticles, respectively.
O
3
2 3
O
2
2 3
O
2 3
O
2
3
dispersed in the polymers. In addition, the average size of g-Fe O
the combustion of the polymer. Another small exothermic peak at
2
3
nanoparticles is 3.5 nm and is uniformly distributed, due to the 466.7 1C in the DSC curve is attributed to the transformation of the
13
inhibition of the growth of the nanocrystals by the polymers.
The morphology and structure of as-synthesized g-Fe –polymer weight loss in the TGA curves at the corresponding temperature.
composites were characterized by transmission electron microscopy Furthermore, there is no phase transformation peak observed in the
TEM), high-angle annular dark-field scanning transmission-electron DSC curve of the composites after calcination at 500 1C (Fig. S3,
2 3 2 3
g-Fe O phase to the a-Fe O phase. Therefore, there is no obvious
2 3
O
(
microscopy (HAADF-STEM), high-resolution TEM (HRTEM), selected- ESI†). Based on these results, iron oxide species can be indexed as
area electron diffraction (SAED) and X-ray diffraction (XRD). The TEM g-Fe O . In addition, the FTIR spectrum (Fig. 2b) exhibits the bonding
2
3
images (Fig. 1a and b) display that the g-Fe O nanoparticles are state of carbon and iron. The peaks centered at 2942, 2857, 1471 and
2
3
À1
uniformly embedded in the polymers, similar to the lotus seeds in the 1390 cm can be assigned to the stretching and deformation
lotus seedpod. The size of g-Fe
on the TEM image and the average size of g-Fe
2
O
3
nanoparticles was measured based vibration of C–H, respectively. A broad peak is observed at ca.
À1
2
O
3
nanoparticles is 3417 cm , which is assigned to OH stretching. The peak centered
À1
15
approximately 3.5 Æ 0.7 nm (inset in Fig. 1b). Moreover, the HAADF- at 1620 cm was ascribed to the stretching vibration of CQO.
À1
À1
STEM image (Fig. 1c) further demonstrated the homogeneity of In addition, the peaks at 592 cm and 457 cm were attributed to
16
g-Fe
played that d-spacings of adjacent fringes were 0.251 nm and analysis (Fig. 2c) was carried out to investigate the oxidation state of
.206 nm, corresponding to the (311) plane and the (400) plane of iron oxide nanoparticles encapsulated in the polymer. Two
g-Fe respectively. The SAED pattern of the composites had three band energies of 724.9 and 711.5 eV are assigned to Fe 2p1/2
visible diffraction rings, which are (311), (400), (440) planes of g-Fe
from the inside out (as shown in the inset in Fig. 1d). Furthermore, major characteristic of Fe in g -Fe
the XRD pattern of the g-Fe –polymer composites had two broad isotherm (Fig. 2d) is similar to the type I isotherm which has a
peaks due to the smaller size nanoparticles embedded in the poly- pronounced slope at very low relative pressure, due to the filling of
2 3
O nanoparticles in the polymers. The HRTEM (Fig. 1d) dis- Fe–O stretching vibration. X-ray photoelectron spectroscopy (XPS)
0
2 3
O
3+
2
O
3
and Fe 2p3/2 of Fe . The satellite peak situated at 719.5 eV is a
3+
17
2 3
O .
The nitrogen sorption
2 3
O
18
mers (Fig. S1, ESI†). In order to confirm the crystal phase of micropores. Moreover, the BET surface area of the composites is
2
À1
nanoparticles, the composites were calcined in air at 350 1C and about 369.5 m g and the pore diameter is 0.55 nm.
00 1C for 2 h, respectively. After calcination at 350 1C, most of the To investigate the influence of the polymer formation on the size of
polymers were burned off, and the nanoparticles were mostly indexed g-Fe nanoparticles, a series of control experiments were conducted
as the maghemite crystal phase, which is in agreement with HRTEM (Table S1, ESI†). When no formaldehyde was added, only g-Fe
5
2 3
O
2 3
O
and SAED data. However, the nanoparticles were transformed into nanoparticles without polymers were obtained and the particle size was
hematite after calcination at 500 1C, because maghemite is thermally about 340 nm (Fig. S4a, ESI†). When 30 mL of formaldehyde was added
13
unstable. Moreover, the room-temperature M o¨ ssbauer spectrum of into the reaction system, g-Fe
O –polymer composites were formed
2 3
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Fig. S4b, ESI†). However, g-Fe
Communication
(
2
O
3
nanoparticles were incompletely (Fig. S8, ESI†). The slight decrease of aniline yield after seven cycles
wrapped in the polymer and the size was not uniform. Interestingly, was probably due to the loss of the catalyst in the transfer process.
4
when the volume of formaldehyde reached 50 mL, the g-Fe O
Compared to the yield in the reported literature and yield obtained
2
3
nanoparticles in the composites were completely embedded in the using commercial g-Fe O , a-Fe O and Fe O (Table S2 and Fig. S9,
2
3
2
3
3 4
polymers and the particle size was about 3.5 nm (Fig. S4c and S4d, ESI†), the composites showed a higher catalytic activity, which should
ESI†). As the concentration of formaldehyde was increased, the be ascribed to the higher surface area of the porous composites and
6
polymer started to form and the g-Fe
2
O
3
nanoparticles in the the smaller size of g-Fe
2
O
3
nanoparticles. Meanwhile, the crystal
polymer gradually became smaller as a result of the inhibition of phase also played a crucial role in catalytic activity. In addition,
growth of g-Fe nanoparticles due to the presence of the polymers. g-Fe –polymer composites also exhibited excellent catalytic
2
O
3
2 3
O
When the concentration of formaldehyde solution was fixed, the performance when different nitroarenes were used as substrates
influence of sodium hydroxide was investigated. When the volume (Table S3, ESI†). Therefore, the g-Fe O –polymer composite
2
3
of sodium hydroxide solution was increased from 0 to 350 mL, the catalyst can be applied in reducing different nitroarenes, which
polymer gradually formed and the size of g-Fe O nanoparticles has potential applications in the catalytic industry.
2
3
gradually became smaller (Fig. S5, ESI†). The reasons were that the
polymerization reaction needed to be undertaken under appropriate synthesis of the g-Fe
alkaline conditions, and the formation of the polymer also prevented thermal decomposition of iron(III) acetylacetonate and formaldehyde
the g-Fe nanoparticles from growing further. Based on the results under the alkaline conditions. The formed polymer inhibited the
of control experiments, we believe that the formation of g-Fe growth of the nanoparticles, and the average size of g-Fe
polymer composites is a result of the combined effects of formalde- nanoparticles was 3.5 nm and these g-Fe O nanoparticles exhibited
In summary, we have developed a facile one-pot approach for the
2 3
O –polymer porous composites through the
2 3
O
2
O
3
–
2 3
O
2
3
hyde and sodium hydroxide. In addition, we also proposed a excellent catalytic activity and recyclability for the reduction of
possible synthetic mechanism (Fig. S6, ESI†). Iron(III) acetylacetonate nitroarene to aminoarene. We believe that our synthetic strategy
decomposed under basic conditions to form iron hydroxide and an can be readily extended to the preparation of other metal oxide–
acetylacetonate anion (compound 1), of which the latter one formed polymer and metal–polymer composites with small particle size.
an acetylacetonate carbanion (compound 2) as a result of the Such composites will find many applications in catalysis, photo-
existing keto–enol tautomerization. The polymer was obtained voltaics, and energy storage.
through the aldol condensation reaction between the acetyl-
This work was supported by NSFC (No. 51001098, 21133010),
acetonate carbanion and formaldehyde. This explained that the Institute of Metal Research (No. 09NBA211A1), MOST (No.
the formation of polymers prevented the g-Fe O nanoparticles 2011CBA00504), and the open project of State Key Laboratory of
2
3
from growing further. To further verify the mechanism, we also Urban Water Resource and Environment (No. QA201023). We
replaced Fe(acac) with FeCl and acetylacetone. The TEM image acknowledge the help of Ms Yanjie Wang and Dr Xin Liu with
Fig. S7, ESI†) of the product shows that the sub-10 nm nano- the M ¨o ssbauer spectroscopy test and analysis.
3
3
(
particles were wrapped in the polymer. The result is in agree-
ment with the hypothesis of the mechanism.
Notes and references
2 3
The catalytic activity of the g-Fe O –polymer composites for the
1
2
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and the particle size of g-Fe nanoparticles was still retained
2 3
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Fig. 3 (a) Reaction equation for the reduction of nitrobenzene to aniline. (b) The
2 3
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1
0090 Chem. Commun., 2013, 49, 10088--10090
This journal is c The Royal Society of Chemistry 2013