Synthesis of polyaniline-modified Fe3O4 /SiO2 /TiO2 composite microspheres and their photocatalytic application
ABSTRACT Polyaniline-modified Fe3O4 /SiO2 /TiO2 composite microspheres have been successfully synthesized by sol–gel reactions on Fe3O4 microspheres followed by the chemical oxidative polymerization of aniline. The synthesized multilayer-structured composites were characterized by TEM, XRD, TGA, UV–vis diffuse reflectance spectra and magnetometer. The photocatalytic activity was evaluated by the photodegradation of methylene blue under visible light. The effect of polyaniline (PANI) amounts on the photocatalytic activity was investigated. The photocatalytic activity results show that the Fe3O4/SiO2/TiO2 composites with about 2.4 wt.%–4.1 wt.% PANI could show higher photocatalytic efficiency than that of Fe3O4/SiO2/TiO2 . Furthermore, the PANI-Fe3O4/SiO2/TiO2 photocatalyst could be easily recovered using a magnet.
Synthesis of polyaniline-modified Fe3O4/SiO2/TiO2composite microspheres and their
Xiubing Huang, Ge Wang⁎, Mu Yang, Wanchun Guo, Hongyi Gao
School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, PR China
a b s t r a c t a r t i c l ei n f o
Received 6 April 2011
Accepted 2 June 2011
Available online xxxx
Polyaniline-modified Fe3O4/SiO2/TiO2composite microspheres have been successfully synthesized by sol–gel
reactions on Fe3O4microspheres followed by the chemical oxidative polymerization of aniline. The synthesized
multilayer-structured composites were characterized by TEM, XRD, TGA, UV–vis diffuse reflectance spectra and
magnetometer. The photocatalytic activity was evaluated by the photodegradation of methylene blue under
visible light. The effect of polyaniline (PANI) amounts on the photocatalytic activity was investigated. The
show higher photocatalytic efficiency than that of Fe3O4/SiO2/TiO2. Furthermore, the PANI-Fe3O4/SiO2/TiO2
photocatalyst could be easily recovered using a magnet.
© 2011 Elsevier B.V. All rights reserved.
In recent years, photocatalysts have attracted increasing attention.
Among the reported photocatalysts, TiO2is an excellent photocatalyst
because of its chemical stability, recyclability, relative low price and
nontoxicity. However, the wide band gap energy of TiO2(Eg=3.2 eV)
limits it to absorb the visible light (λN380 nm) and this disadvantages
its wide use. Hence, intense research has been reported to lower its
band gap, such as doping TiO2with metals (W , Fe , et al.) or
nonmetal atoms (C , S , et al.).
Recently, conducting polymers (e.g., PANI) modified TiO2 was
reported to exhibit a significantly better photocatalytic activity than
that of pure TiO2under visible light irradiation . PANI, due to its
delocalized conjugated structures in electron-transfer processes, can be
photocatalytic activityundervisiblelight .However, onlyconducting
polymer doped TiO2is not favorable due to its difficulty to be separated
from large volumes of treated effluent. Magnetic separation provides a
convenient means to remove magnetizable species by applying an
appropriate magnetic field . Some reports show that titania
supported by magnetic nanoparticles (Fe3O4, γ-Fe2O3, etc.) provides
an effective approach, while their photocatalytic efficiency in organic
pollutant degradation under visible light needs be further improved
[8–10]. Several groups have done some work to improve the photo-
catalytic activity of magnetic photocatalysts by depositing TiO2with
to degrade organic pollutants.
In this work, PANI-modified Fe3O4/SiO2/TiO2 composite micro-
spheres were synthesized and their photocatalytic activity was
evaluated by the degradation of methylene blue under visible light.
The influence of PANI amounts on the activity was investigated.
2.1. Synthesis of Fe3O4/SiO2/TiO2composite microspheres
Fe3O4/SiO2 microspheres were prepared according to previous
research . First, Fe3O4 microspheres were prepared through a
as reaction materials. Then, Fe3O4/SiO2microspheres were synthesized
through a sol–gel method using tetraethyl orthosilicate as silica source
microspheres were magnetically collected, washed with ethanol and
water, and then dried.
The Fe3O4/SiO2/TiO2 composite microspheres were synthesized
through a sol–gel method. Briefly, 0.10 g Fe3O4/SiO2 microspheres
were dispersed into a solution which consisted of 1 mL TBT and 35 mL
ethanol with the aid of ultrasonication for 10 min. After that, 2 mL of
magnetic stirring. Subsequently, the suspension was stirred for 2 h at
room temperature and successively magnetically collected and washed
with ethanol for several times. After being oven-dried, the powders
obtained were calcined at 450 °C for 2 h.
Materials Letters 65 (2011) 2887–2890
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2.2. Synthesis of PANI-Fe3O4/SiO2/TiO2composite microspheres
PANI-Fe3O4/SiO2/TiO2composite microspheres were prepared by a
0.20 g Fe3O4/SiO2/TiO2 composite microspheres were ultrasonically
dispersed into 20 mL 0.2 mol/L HCl aqueous solution for 10 min.
Quantitative aniline was added into this mixture under stirring in the
ratio of (NH4)2S2O8to aniline was 1:1) was added to the reaction
solution. After stirred for 12 h, the PANI-modified Fe3O4/SiO2/TiO2
composite microspheres were magnetically separated and rinsed
with water, alcohol, and finally dried. In this experiment, different
initial volumes of aniline were used to modify Fe3O4/SiO2/TiO2
composite microspheres. The obtained powders were referred to as
PANI(x)-Fe3O4/SiO2/TiO2, in which x is the volumes (mL) of aniline
The morphology of all the samples was observed on a JEOL
JEM-100CX II transmission electron microscopy (TEM). The powder
XRD patterns were recorded on a M21X diffractometer using a Cu Ka
radiation. The thermogravimetric analysis (TGA) was carried out on a
NETZSCH STA449F3 at a heating rate of 10 °C min−1under nitrogen.
Magnetic studies were carried out on a HH-15 vibrating sample
2.4. Photocatalytic activity test
The photocatalytic activity of these samples was evaluated by the
degradation of methylene blue, which was exposed under visible light
by removing light below than 420 nm using a filter. A circulating water
jacket was used to cool the reaction vessel. 100 mL methylene blue
aqueous solution with the concentration of 10 mg L−1was mixed with
0.5 g L−1catalysts in an optically matched pyrex vessel. Before the
irradiation, the suspension was stirred in a dark condition for 30 min
solution were taken away every 40 min from the reactor and the
concentration of methylene blue was analyzed by a 2000 UV–vis
spectrometer and calculated by a calibration curve. Methylene blue
photoactivity experiment, the photocatalysts were magnetically
collected, and then rinsed with water for the further use.
3. Results and discussion
SiO2/TiO2 are shown in Fig. 1. The TEM image shows that Fe3O4
200 nm (Fig. 1a). After successively coated with SiO2, TiO2and PANI,
these composite microspheres have multilayer structures and some
microspheres are linked together. Furthermore, the yield of the
core/shell structure spheres is 100% and the SiO2shells are about
15 nm in thickness (Fig. 1b). After coated with TiO2, the microspheres
are linked together and the surfaces are rougher thanthatof Fe3O4/SiO2
microspheres (Fig. 1c). The amount of PANI onto Fe3O4/SiO2/TiO2
increases with the increasing volumes of aniline added. The TEM image
of PANI(0.008)-Fe3O4/SiO2/TiO2(Fig. 1f) shows thatPANIparticleswith
a diameter of about 20 nm can be obtained on the surfaces.
Fig. 2 shows the XRD patterns of Fe3O4, Fe3O4/SiO2, Fe3O4/SiO2/TiO2
and PANI(0.008)-Fe3O4/SiO2/TiO2. The XRD pattern of Fe3O4 is in
agreement with the JCPDS card No. 19–0629 (Fig. 2a). The coating of
SiO2layer does not change the structure of Fe3O4(Fig. 2b). In addition,
Fe3O4/SiO2/TiO2is composed of anatase TiO2(JCPDS card No. 21–1272)
along with the magnetic phase (Fig. 2c). The peak positions of PANI-
modified Fe3O4/SiO2/TiO2and Fe3O4/SiO2/TiO2donot have any changes
The results of the photodegradation of methyleneblue are shown in
Fig. 3. The results show that the introduction of about 2.4wt.%–4.1 wt.%
Fig. 1. TEM images of (a) Fe3O4, (b) Fe3O4/SiO2, (c) Fe3O4/SiO2/TiO2, (d) PANI(0.004)-Fe3O4/SiO2/TiO2, (e) PANI(0.006)-Fe3O4/SiO2/TiO2, and (f) PANI(0.008)-Fe3O4/SiO2/TiO2
X. Huang et al. / Materials Letters 65 (2011) 2887–2890
PANI to Fe3O4/SiO2/TiO2obviously enhances the photocatalytic activity
and PANI(0.006)-Fe3O4/SiO2/TiO2with PANI amount of about 2.7 wt.%
has the highest photocatalytic efficiency. The UV–vis diffuse reflectance
spectra of Fe3O4/SiO2/TiO2 and PANI(0.006)-Fe3O4/SiO2/TiO2
(not shown) confirm that PANI-modified Fe3O4/SiO2/TiO2has higher
absorption in the visible light region and lower absorption in the UV
region thanpure Fe3O4/SiO2/TiO2, indicating that the absorption of TiO2
is enhanced in the visible light region after modification by PANI. The
photocatalytic activity of PANI-modified Fe3O4/SiO2/TiO2 composite
microspheres is higher than that of Fe3O4/SiO2/TiO2, and the results can
be attributed to the dye photosensitization and the synergetic effect of
PANI and TiO2. The delocalized conjugated structures of PANI can
enhance the charge separation efficiency by photoinduced carrier
transfer. Under the visible light irradiation, the excited electrons
generated by π–π* transition of PANI can be delivered into the
conduction band of TiO2, and then to an adsorbed electron acceptor,
yielding oxygenous radicals to degrade pollutants . However,
further increasing the amount of PANI to 4.1 wt.% for PANI(0.008)-
better than that of Fe3O4/SiO2/TiO2. The results can be ascribed to
different transferring rates of the photoinduced carriers and recombi-
nation of electron-holes pairs when different amounts of PANI are
The narrow band of iron oxides is thought to lead to an increase in
the incidence of electron–hole recombination and it will lower the
photoactivity . The SiO2intermediate layer between iron oxides
core and TiO2 shell can promote the photocatalytic activity by
decreasing the electronic interactions at the point of contact
(heterojunctions) . Thus in this work, a SiO2layer with thickness
about 15 nm was usedto coat iron oxidecorethrough sol–gel method.
What's more, the SiO2layer protects the Fe3O4core from etching in
harsh application occasions.
Fig. 4 presents the magnetization curves measured at 300 K for the
prepared samples. After coated with SiO2, TiO2and PANI, the saturation
magnetization of Fe3O4(Fig. 4a) decreased obviously. However, the
which can facilitate the separation of photocatalysts from treated
Fe3O4/SiO2/TiO2composite microspheres were successfully coated
The Fe3O4/SiO2/TiO2 composite microspheres modified with about
2.7 wt.% PANI can show the highest photocatalytic activity in the
photodegradation of methylene blue under the visible light illumina-
tion. The PANI-modified Fe3O4/SiO2/TiO2composite microspheres can
be easily recovered by a magnetite after the reaction. This approach
provides a general method to synthesize other conjugated organics
modified magnetic photocatalysts.
We thank the National Natural Science Foundation of China (Grant
No. 51073023) and the Fundamental Research Funds for the Central
Universities (FRF-TP-09-009B) for their support.
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