Direct coating ZnO nanocrystals onto 1D Fe3O4/C composite microrods as highly efficient and reusable photocatalysts for water treatment

Article abstract of DOI:10.1016/j.jallcom.2015.03.033

In this wok, we demonstrated a facile two-step method to directly coat a ZnO nanocrystal layer on the surface of one-dimensional (1D) Fe₃O₄/C composite microrods to form Fe₃O₄/C@ZnO core-shell microrods. Firstly, 1D Fe₃O₄/C composite microrods were successfully synthesized by one-pot magnetic field-induced solvothermal reaction according to our previous work. Sencondly, a uniform ZnO nanocrystal layer was facilely coated onto the 1D Fe₃O₄/C composite microrods via a modified hydrothermal process at a low temperature (60 °C). Importantly, the size of ZnO nanocrystals and the thickness of coating layer can be easily tuned by varying the concentration of Zn(Ac)₂·2H₂O in the solution. Further investigation has revealed that the as-prepared core-shell microrods exhibited enhanced photocatalytic activity for the decolorization of photosensitized dyes (Congo red) under visible-light illumination. Moreover, these magnetically separable photocatalysts can be readily recycled by a magnet with virtually no loss in catalytic efficiency. We believe this facile synthesis strategy provides a general and efficient way to synthesize other 1D magnetic nanocomposites for different functional applications.

Full text of DOI:10.1016/j.jallcom.2015.03.033

Journal of Alloys and Compounds 637 (2015) 301–307
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jalcom
Direct coating ZnO nanocrystals onto 1D Fe3O4/C composite microrods
as highly efficient and reusable photocatalysts for water treatment
a,
Yanrong Wang a,1, Jiqiang Ning b,1, Enlai Hu a, Changcheng Zheng b,c, Yijun Zhong a, , Yong Hu
⇑
⇑
a Institute of Physical Chemistry, Zhejiang Normal University, Jinhua 321004, PR China
b Department of Physics and HKU-CAS Joint Laboratory on New Materials, The University of Hong Kong, Pokfulam Road, Hong Kong, China
c Mathematics and Physics Centre, Department of Mathematical Sciences, Xi’an Jiaotong-Liverpool University, Suzhou 215123, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
In this wok, we demonstrated a facile two-step method to directly coat a ZnO nanocrystal layer on the
surface of one-dimensional (1D) Fe3O4/C composite microrods to form Fe3O4/C@ZnO core–shell micro-
rods. Firstly, 1D Fe3O4/C composite microrods were successfully synthesized by one-pot magnetic
field-induced solvothermal reaction according to our previous work. Sencondly, a uniform ZnO nanocrys-
tal layer was facilely coated onto the 1D Fe3O4/C composite microrods via a modified hydrothermal pro-
cess at a low temperature (60 °C). Importantly, the size of ZnO nanocrystals and the thickness of coating
layer can be easily tuned by varying the concentration of Zn(Ac)2Á2H2O in the solution. Further investiga-
tion has revealed that the as-prepared core–shell microrods exhibited enhanced photocatalytic activity
for the decolorization of photosensitized dyes (Congo red) under visible-light illumination. Moreover,
these magnetically separable photocatalysts can be readily recycled by a magnet with virtually no loss
in catalytic efficiency. We believe this facile synthesis strategy provides a general and efficient way to
synthesize other 1D magnetic nanocomposites for different functional applications.
Received 31 December 2014
Received in revised form 2 March 2015
Accepted 3 March 2015
Available online 10 March 2015
Keywords:
Composite microrods
ZnO nanocrystals
Core–shell nanostructure
Magnetic field-induced
Photodecolorization
Ó 2015 Elsevier B.V. All rights reserved.
1. Introduction
through coordination or electrostatic interactions in solution [13].
Therefore, amorphous carbon can be used as unique coating or
Photocatalytic degradation of toxic organic compounds by
semiconductor nanomaterials using inexhaustible solar energy
has become a modern water treatment technology in recent years
[1]. However, the separation of photocatalysts from large volumes
of reaction solution remains a challenge in practical applications.
Therefore, it is highly desirable to develop a reliable approach for
realization of photocatalyst recycling [2,3]. Fortunately, magnetic
materials can be collected easily by an external magnetic field,
which can act as a carrier to facilitate material separation and recy-
cling in aqueous solutions [4–6]. Therefore, the combination of
photocatalysts and magnetic materials has an advantageous pro-
spect in the photodegradation process [7–10]. In order to protect
the magnetic particles from chemical degradation or agglomera-
tion in practical applications, it is necessary to coat the magnetic
material with an organic or inorganic shell [11,12]. Because the
surface of the amorphous carbon is hydrophilic and has abundant
amounts of –OH and -COOÀ groups, which can bind metal cations
supporting material for different applications [14–16].
Very recently, we have successfully synthesized 1D magnetic
Fe3O4/C composite microrods by a one-pot magnetic field-induced
solvothermal method, which demonstrate much better lithium
storage properties than Fe3O4 nanospheres [17]. Considering the
requirement of photocatalysts in practical applications, these 1D
magnetic Fe3O4/C composite microrods can offer multifold advan-
tages: (a) introduction of additional functionalities due to the pres-
ence of abundant surface reactive groups, which can act as an
excellent supporting material to bind other semiconductor photo-
catlysts for realization of rapid recycling [18]. (b) The magnetic
component might not only prevent the agglomeration of the cata-
lyst nanocrystals during recovery, but also offer some synergetic
enhancement of the catalytic activity by forming the hybrid
structure [19]. (c) 1D nanostructures with the unique structure of
anisotropy, low dimension and enhanced aspect ratio, are consid-
ered to be beneficial for photocatalytic and electrochemical
performance since they facilitate electron and ion transport
[20–22]. (d) The presence of amorphous carbon in 1D magnetic
Fe3O4/C microrods not only promotes the absorption of light, but
also accelerates the electron transfer, thus improving the
photocatalytic efficiency [23].
⇑
Corresponding authors. Tel.: +86 579 82282234; fax: +86 579 82282595.
E-mail address: yonghu@zjnu.edu.cn (Y. Hu).
1
These authors contributed equally to this work.
http://dx.doi.org/10.1016/j.jallcom.2015.03.033
0925-8388/Ó 2015 Elsevier B.V. All rights reserved.

302
Y. Wang et al. / Journal of Alloys and Compounds 637 (2015) 301–307
Scheme 1. Schematic illustration of the formation of 1D Fe3O4/C@ZnO core–shell composite microrods.
Table 1
As one of the most important multifunctional semiconductor
Control of ZnO particle size in 1D Fe3O4/C@ZnO composite microrods using different
materials, ZnO has been widely noted and studied due to their
low-cost, high quantum efficiency and high photocatalytic activity
and stability [24–29]. Because the synthetic methods of ZnO nano/
micro-structures are usually simple, low-temperature, non-toxic,
environmentally-friendly [30–36], ZnO has been regarded as a
promising photocatalytic material for realizing commercialization.
In this study, as a proof-of-concept demonstration of the functional
properties of the as-prepared 1D Fe3O4/C composite microrods, we
choose ZnO nanocrystal as a coating layer to form Fe3O4/C@ZnO
core–shell microrods, which exhibit obviously enhanced photocat-
alytic activity and excellent recyclability for the decolorization of
photosensitized dye Congo red (CR) under visible-light
illumination.
The detailed synthesis process is schematically demonstrated in
Scheme 1. Firstly, 1D Fe3O4/C composite microrods were synthe-
sized by one-pot magnetic-field inducing solvothermal method
[17]. Secondly, a uniform ZnO nanocrystal layer was deposited
on the surface of 1D Fe3O4/C microrods through a facile modified
hydrothermal process, which only requires Zn(Ac)2Á2H2O and
NaOH as reagents reacting at 60 °C for 2 h in water. It is found that
the size of ZnO nanocrystals and the thickness of shell layer can
also be tuned by varying the concentration of precursors.
Furthermore, the 1D Fe3O4/C@ZnO core–shell microrods not only
exhibit excellent photocatalytic activity for the decolorization of
CR under visible-light irradiation, but also can be readily recycled
by a simple magnet with virtually no loss in catalytic efficiency.
Therefore, this design provides a promising candidate for removing
toxic organic pollutants during water treatment process.
Zn2+ concentrations.
Sample Zn2+ concentration/ NaOH concentration/ ZnO particle size/
M
M
nma
Sa
Sb
Sc
Sd
0.0031
0.0063
0.0125
0.0250
0.0063
0.0125
0.0250
0.0500
9.0
11.1
13.7
17.6
a
ZnO particle size was calculated from XRD diffraction data.
groups (e.g., carboxylic) of the Fe3O4/C composites. Then, 5 mL of NaOH aqueous
solution was dropwise added and kept stirring at 60 °C for 2 h. Finally, the product
was collected by a magnet, and washed with distilled water and ethanol for several
times, then dried in an oven at 60 °C for 6 h. In order to optimize the properties of
the 1D Fe3O4/C@ZnO core–shell microrods for photocatalytic applications, different
concentrations of Zn(Ac)2Á2H2O and also corresponding NaOH were used, while the
other conditions remain unchanged. Products prepared with different concentra-
tions of Zn(Ac)2Á2H2O (0.0031, 0.0063, 0.0125 and 0.0250 M) by seeding and growth
process were assigned to sample codes Sa, Sb, Sc and Sd, respectively (see Table 1).
2.3. Characterization
Powder X-ray diffraction (XRD) measurements of the samples were performed
with a Philips PW3040/60 X-ray diffractometer using Cu Ka radiation at a scanning
rate of 0.06°sÀ1. Scanning electron microscopy (SEM) images were obtained by a
Hitachi S-4800 scanning electron microanalyzer with an accelerating voltage of
15 kV. Transmission electron microscopy (TEM) and high-resolution transmission
electron microscopy (HRTEM) were conducted at 200 kV with a JEM-2100F field
emission TEM. Further evidence for the composition of the products was inferred
from X-ray photoelectron spectroscopy (XPS), using an ESCALab MKII X-ray
photoelectron spectrometer with Mg Ka X-ray as the excitation source. The absorp-
tion spectra were measured using a PerkinElmer Lambda 900 UV–vis spectropho-
tometer at room temperature.
2. Experimental details
2.4. Photocatalytic activity measurement
All reagents were analytical grade, purchased from the Shanghai Chemical
Reagent Factory, and used as received without further purification.
Photocatalytic activities of the as-prepared 1D Fe3O4/C@ZnO core–shell com-
posite microrods were evaluated by the degradation of CR under visible-light
irradiation from a 500 W Xe lamp (CEL-HXF300) with a 420 nm cut off filter. The
reaction cell was placed in a sealed black box with the top opened, and the cut
2.1. Synthesis of 1D Fe3O4/C composite microrods
1D Fe3O4/C microrods were prepared according to our previous work [17].
Briefly, 0.4 g of FeCl3Á6H2O and 0.3 g of NaAc were dispersed into a mixed solvent
of 15 mL of ethylene glycol and 3 mL of ethylenediamine with the assistance of
ultrasonication. Then, 0.4 g of glucose was added into the above suspension, and
the resulting mixture was transferred into a 20 mL of Teflon-lined stainless steel
autoclave in the presence of an external magnetic field (0.2 T), and heated at
180 °C for 6 h. Finally, the as-obtained Fe3O4/C composite microrods were collected
and washed with distilled water and ethanol for several times by centrifugation,
then dried in an oven at 60 °C for 6 h.
off filter was placed to provide visible-light irradiation. In
a typical process,
20 mg of as-prepared photocatalysts was added into 20 mL of CR solution (concen-
tration: 100 mg LÀ1). After being dispersed in an ultrasonic bath for 5 min, the solu-
tion was stirred for 2 h in the dark to reach adsorption equilibrium between the
catalyst and the solution and then exposed to visible-light irradiation. The samples
were collected by a magnet at given time intervals to measure the CR concentration
by UV–vis spectroscopy. To further study the recyclability of the 1D Fe3O4/C@ZnO
core–shell composite microrods, we also examined the photocatalytic activity of
sample Sd for 10 rounds. The recycled photocatalyst sample was reused without
any post-treatment except being washed with ethanol and distilled water three
times after each photocatalytic degradation of CR.
2.2. Synthesis of 1D Fe3O4/C@ZnO core–shell microrods
ÅOH radical reactions were performed as follows. 5 mg of each 1D Fe3O4/C@ZnO
core–shell composite microrods with different ZnO nanocrystal sizes were
suspended in 10 mL of aqueous solution containing 100 mg LÀ1 of CR, 10 mM of
NaOH and 5 mM of terephthalic acid (TA), respectively. Before exposure to
visible-light, the suspension was stirred in the dark for 10 min.
After irradiated for 10 min, the products were collected by a magnet, and the rest
In a typical procedure, a certain amount of Zn(Ac)2Á2H2O was added into 20 mL
of distilled water to form a clear solution. 50 mg of Fe3O4/C composite microrods
was added to the above solution with the assistance of sonication for 10 min.
Subsequently, the mixture was stirred by a mechanical stirring, followed by heating
at 60 °C for 2 h to allow the Zn2+ ions fully interact with the surface functional

Y. Wang et al. / Journal of Alloys and Compounds 637 (2015) 301–307
303
of solution was collected for fluorescence spectroscopy measurements. A fluores-
cence spectrophotometer was then used to measure the fluorescence signal of the
generated 2-hydroxy-terephthalic acid (TAOH). The excitation light wavelength
used in recording fluorescence spectra was 320 nm.
The SEM images of the as-prepared 1D Fe3O4/C@ZnO core–shell
microrods synthesized with the different Zn(AC)2 concentrations
are shown in Fig. 3. These images depict microrods with nearly
uniform size, about 1–1.5 lm in diameter and several micrometers
in length. Besides, the rod morphology of all samples is well pre-
served without any observable impurity particles or aggregates.
With increasing the concentration of Zn2+, obvious changes of the
microrod surface can be observed from Fig. 3a–d. Specifically, the
size of ZnO nanocrystals on the surface of 1D Fe3O4/C microrods
becomes larger and the diameter of 1D Fe3O4/C@ZnO core–shell
microrods increases gradually. For comparison, the SEM image of
1D Fe3O4/C composite microrods was shown in Fig. 2b. It is clearly
seen that the surface of 1D Fe3O4/C@ZnO core–shell composite
microrods was rougher than that of the 1D Fe3O4/C composite
microrods.
Further morphology and structure characterizations of the as-
prepared samples are elucidated by TEM observation. Fig. 4a–d
shows the typical TEM images of 1D Fe3O4/C@ZnO core–shell
microrods loaded with different amounts of ZnO, respectively.
The inset in Fig. 4a shows the HRTEM of sample Sa, which demon-
strates that the ZnO coating layer is successfully deposited on the
surface of 1D Fe3O4/C microrods. From the HRTEM image (the inset
in Fig. 4d), clear lattice fringes of ZnO coating layer can be observed
and match well with hexagonal phase of ZnO with lattice spacing
at 0.25 nm and 0.28 nm corresponding to the (101) planes and
(100) plane of ZnO. From all TEM images, it can be clearly seen
that ZnO coating layer was uniformly deposited on the surface of
1D Fe3O4/C microrods, and the thickness of ZnO coating layer
increases gradually with increasing the concentration of precur-
sors. The thickness of ZnO coating layer of Sa, Sb, Sc, and Sd are
about 25 nm, 45 nm, 110 nm and 200 nm, respectively. These
results are in good agreement with the XRD and SEM analyses.
Additionally, the chemical states of elements in the 1D Fe3O4/
C@ZnO core–shell composite microrods are further studied by
the XPS technique. A typical survey spectrum of the 1D Fe3O4/C/
ZnO composite microrods is depicted in Fig. S1 (see the
Supporting Information), which displays the presence of O, C, Zn,
and Fe elements. Fig. 5a displays a high-resolution spectrum of
Zn, the peaks at 1021.0 eV and 1044.0 eV correspond to Zn 2p3/2
and 2p1/2, respectively [37]. In the spectrum of Fe2p (Fig. 5b),
the Fe2p3/2 and Fe2p1/2 peaks are located at 710.3 and 724.0 eV
3. Results and discussion
The crystallographic structure and phase purity of the as-pre-
pared 1D Fe3O4/C@ZnO core–shell microrods were examined by
XRD measurements. As shown in Fig. 1, the diffraction peaks in
the XRD patterns marked with empty triangles can be assigned
to face-centered cubic magnetite Fe3O4 (JCPDS standard card No.
19-0629. a = 8.396 Å). Other diffraction peaks marked by asterisks
can be well indexed to hexagonal phase of ZnO (JCPDS standard
card No. 36-1451. a = b = 3.250 Å and c = 5.207 Å). Because the
(440) diffraction peak of Fe3O4 is very adjacent to the (103)
diffraction peak of ZnO, two peaks are overlapped together. With
increasing amount of Zn2+ ion, the diffraction intensity of the
strongest ZnO (100) peak increases gradually, indicating that the
ZnO nanocystals grow larger with better crystallinity. The
corresponding particle sizes of ZnO with the different Zn2+ concen-
trations are listed in Table 1, which confirming that the ZnO nano-
particles grow larger with better crystallinity. In addition, the XRD
pattern of the 1D Fe3O4/C composite microrods is shown in Fig. 2a.
Ƹ
ZnO
Fe3O4
*
Ƹ
Ƹ
Ƹ
Ƹ
Ƹ
*
*
Ƹ
*
Sd
Sc
*
*
*
*
Sb
Sa
20
30
40
50
60
70
respectively. The characteristic satellite peak at 719.0 eV of
a-
2θ (degree)
Fe2O3 or -Fe2O3 is not observed [38–40], indicating the pure
c
Fe3O4 phase in 1D Fe3O4/C@ZnO core–shell microrods. Fig. 5c
shows a high-resolution spectrum of O 1s, which can be deconvo-
luted into three peaks by the XPS peak fitting program. The peaks
Fig. 1. XRD patterns of as-prepared 1D Fe3O4/C@ZnO core–shell composite
microrods loaded with different amounts of ZnO, denoted as Sa, Sb, Sc, and Sd,
respectively.
Fig. 2. XRD pattern (a) and SEM image and (b) of the 1D Fe3O4/C composite microrods.

304
Y. Wang et al. / Journal of Alloys and Compounds 637 (2015) 301–307
Fig. 3. Sem images of as-prepared 1D Fe3O4/C@ZnO core–shell composite microrods loaded with different amounts of ZnO, (a) Sa, (b) Sb, (c) Sc and (d) Sd.
Fig. 4. TEM images of as-prepared 1D Fe3O4/C@ZnO composite microrods loaded with different amounts of ZnO, (a) Sa, (b) Sb, (c) Sc and (d) Sd.
at 530.2 and 531.9 eV can be attributed to O in Fe3O4 and ZnO,
respectively [41,42]. The peak at 531.0 is associated with the O2À
ions in the oxygen-deficient regions within the ZnO matrix [43].
The high-resolution spectrum of C1s is displayed in Fig. 5d, which
also can be resolved into three peaks. The core level spectrum in
the C1s region displays an asymmetric broad peak, which indicates
that more than one chemical states of C are present [44]. By fitting
the experimental line profile, three peaks are identified and

Y. Wang et al. / Journal of Alloys and Compounds 637 (2015) 301–307
305
assigned to the aliphatic C–C bond (284.7 eV), O–C–O complex
(286.1 eV), and carbonate species (288.5 eV) [23,45]. The higher
binding energy suggests the carbon may be incorporating into
the interstitial positions of the Fe3O4 lattice, and also the possibly
of such defect complexes that involve C–O bonds [38,46].
composite microrods as photocatalysts was also investigated by
collecting and reusing the same photocatalyst for multiple cycles.
As shown in Fig. 6b, where the sample Sd was used for the
reusability test, the photocatalytic activity does not show signifi-
cant loss up to 10 cycles of photo-decolorization of CR dye, indicat-
ing the excellent stability of samples. Furthermore, the magnetic
recyclable photocatalysts are also favorable because of the great
ease in separation from the reaction solution by a magnet after
each degradation reaction. Thus, the results suggest that the mag-
netic 1D Fe3O4/C@ZnO core–shell composite microrods are stable
and have great application potential in water treatment.
We speculate that the decolorization of dyes is mainly due to
the photosensitization process because that ZnO has no apparent
absorption in the visible-light region. Dye rather than ZnO is
excited by visible light to form excited Dye (Dye⁄). Dye⁄ can
directly inject electrons into the conduction band of ZnO semicon-
ductor, forming conduction band electrons, the electron is trapped
by surface adsorbed O2 to generate various reactive oxidative spe-
cies (ROSs), the dye⁄ subsequently self-degrades or is degraded by
ROSs. Thus, the decolorization efficiency greatly depends on the
electron transfer between the dye⁄ and the as-prepared nanohy-
brids [24,35,48,49]. The relative band edge alignment of different
components was illustrated in Fig.S2 (see the Supporting
Information).
The photocatalytic activities of the as-prepared 1D Fe3O4/
C@ZnO core–shell microrods were evaluated by the decolorization
of CR in water. Fig. 6a displays the decolorization behavior of CR in
the absence of any photocatalyst (that is, the blank test), in the
presence of commercial ZnO powder, the as-prepared 1D Fe3O4/C
composite microrods and 1D Fe3O4/C@ZnO core–shell microrods
after exposure to visible-light irradiation, where C is the concentra-
tion of CR after different light irradiation time intervals and C0 is
the initial concentration of the CR before dark adsorption. After
visible light irradiation for 60 min, approximately 59.8% of CR is
decolorized using commercial ZnO as the photocatalyst, while
17.8% of CR is decolorized in the presence of 1D Fe3O4/C microrods.
The decolorization fractions using 1D Fe3O4/C@ZnO composite
microrods (Sa, Sb, Sc and Sd) as photocatalysts are about 60.4,
70.5%, 81.5%, and 96.7%, respectively. This result indicates that
the decolorization efficiency enhanced by increasing loading
amount of ZnO is more active than commercial ZnO. The particle
size of commercial ZnO powder is about 41.8 nm estimated using
the Debye–Scherrer equation according to our previous work
[35]. Thus, the enhanced decolorization efficiency of the as-pre-
pared 1D Fe3O4/C@ZnO core–shell composite microrods may be
ascribed to the unique 1D microrod structure and the presence of
amorphous carbon, both of which could accelerate the transport
of electrons, promoting the separation of photogenerated charges,
as well as the dispersion of composite microrods in an aqueous
solution allowing more reactive sites for adsorption and decol-
orization of CR [47]. The reusability of the 1D Fe3O4/C@ZnO
In this hybrid structure, the electrons in the conduction band of
ZnO can easily transfer to 1D Fe3O4/C microrods, which contribute
to improve effective separation of electrons and holes.
Additionally, 1D Fe3O4/C microrod is believed to be beneficial for
achieving higher photocatalytic performance since it facilitates
electron transport [50]. To verify this speculation, we measure
Å
the OH radicals formed in different 1D Fe3O4/C@ZnO core–shell
microrods obtained with different Zn(AC)2 concentrations
b
a
Fe2p3/2
Fe2p1/2
1010
1020
1030
1040
1050
1060
705 710 715 720 725 730 735 740
Binding Energy (eV)
Binding Energy (eV)
c
d
C1s
O1s
526
528
530
532
534
536
282
284
286
288
290
292
Binding Energy (eV)
Binding Energy (eV)
Fig. 5. XPS spectra of as-prepared 1D Fe3O4/C@ZnO core–shell composite microrods: (a) Zn2p spectrum, (b) Fe2p spectrum, (c) O1s spectrum and (d) C1s spectrum.

306
Y. Wang et al. / Journal of Alloys and Compounds 637 (2015) 301–307
100
a
b
1.0
0.8
0.6
0.4
0.2
0.0
blank
80
Fe3O4/C
60
commercial ZnO
40
Sa
Sb
20
Sc
Sd
60
0
1
2
3
4
5
6
7
8
9
10
50
0
10 20
30 40
Cycle number
Time (min)
Fig. 6. (a) Photocatalytic degradation of CR in the absence of any photocatalyst (the blank test), with 1D Fe3O4/C microrods, commercial ZnO and in the presence of 1D Fe3O4/
C@ZnO core–shell composite microrods loaded with different amounts of ZnO: (a) Sa, (b) Sb, (c) Sc and (d) Sd. (b) 10 cycles of the degradation of CR using sample Sd as the
photocatalyst under visible light irradiation for 60 min.
was shown in Fig. S3 (see Supporting Information). After IR light
irradiation for 60 min, approximately 5% of CR is decolorized
using 1D Fe3O4/C@ZnO core–shell composite microrods as the
photocatalyst, which indicates that the effect of
Sd
Sc
Sb
IR on photocatalytic activity can be negligible.
Sa
without catalyst
4. Conclusions
In summary, a facile two-step method has been developed to
prepare 1D Fe3O4/C@ZnO core–shell microrods through a magnetic
field-induced solvothermal route followed by
a
modified
hydrothermal process. Importantly, the size of ZnO nanocrystals
and the thickness of coating layer can be conveniently controlled
by varying the concentration of Zn2+ during the synthesis process.
These 1D Fe3O4/C@ZnO core–shell microrods exhibit excellent
photostability and enhanced photodecolorization of CR dye under
visible-light irradiation. The superior visible-light photocatalytic
activity may be attributed to the unique 1D microrods structure
and the presence of amorphous carbon, both of which could accel-
erate the transport of electrons, promoting the separation of
photogenerated charges. We believe this facile synthesis method
can be extended to produce other 1D magnetic nanocomposites
containing 1D magnetic-carbon structure as the support and an
outer layer of active nanomaterials for different applications.
350
375
400
425
450
475
500
525
Wavelength (nm)
Fig. 7. Fluorescence spectra of TAOH formed by the reaction of TA with ÅOH radicals
generated from different samples (Sa, Sb, Sc and Sd) compared with no catalyst
under visible-light irradiation for 10 min.
compared to that without catalysts in the presence of CR using a
similar method described previously, which can be used to demon-
strate the separation efficiency of photogenerated electrons and
Acknowledgements
Financial support from the Natural Science Foundation of China
(21171146, 21371152) and Zhejiang Provincial Natural Science
Foundation of China (LR14B010001, LR12B040001) are gratefully
acknowledged.
Å
holes in the hybrid system [51]. It is well known that OH reacts
with terephthalic acid (TA) in basic solution to generate 2-hy-
droxy-terephthalic acid (TAOH), which emits a unique fluores-
cence signal with the peak centered at 426 nm [52]. Significant
fluorescent signals associated with TAOH are generated upon visi-
ble-light irradiation of the different photocatalysts suspended, and
no catalysts in a TA solution in the present of CR for 10 min. As
Appendix A. Supplementary material
Å
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.jallcom.2015.03.
033.
shown in Fig. 7, it can be seen that OH radicals are formed in the
solution with different photocatalysts in presence of CR in the pho-
toreaction process under visible light irradiation. Obviously, fluo-
rescence intensity increases with increasing loading amount of
ZnO. When there is only CR in a TA solution, the emission peak
of TAOH could also be observed, but it is much weaker than those
of in the presence of 1D Fe3O4/C@ZnO core–shell microrods.
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Furthermore, the most OH radicals are formed using sample Sd
in the decolorization process, and this result is in a good agreement
with that of decolorization of dyes. In order to investigate
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