Fabrication of magnetically recyclable Fe3O4@Cu nanocomposites with high catalytic performance for the reduction of organic dyes and 4-nitrophenol

Materials Chemistry and Physics 148 (2014) 639e647

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Fabrication of magnetically recyclable Fe3O4@Cu nanocomposites with high catalytic performance for the reduction of organic dyes and 4-nitrophenol Mingyi Tang a, *, Sai Zhang a, Xianxian Li a, Xiaobo Pang a, Haixia Qiu b, ** a b

Department of Applied Chemistry, School of Science, Tianjin University of Commerce, Tianjin 300134, PR China School of Science, Tianjin University, Tianjin 300072, PR China

h i g h l i g h t s
Cu nanoparticles as small as 3 nm are synthesized.
Low cost Fe3O4@Cu magnetical nanoparticles show catalytic activity for organic dyes and 4-nitrophenol.
The Fe3O4@Cu display high catalytic activity after 13 cycles.

a r t i c l e i n f o

a b s t r a c t

Article history: Received 26 March 2014 Received in revised form 11 July 2014 Accepted 16 August 2014 Available online 10 September 2014

A facile and efficient approach to synthesize Fe3O4@Cu nanocomposites using L-Lysine as a linker was developed. The morphology, composition and crystallinity of the Fe3O4@Cu nanocomposites were characterized by Fourier Transform infrared spectroscopy, transmission electron microscopy, energydispersive X-ray spectroscopy, and powder X-ray diffraction. In addition, the magnetic properties were determined with vibrating sample magnetometer. The surface of the Fe3O4 contained many small Cu nanoparticles with sizes of about 3 nm. It was found that the Fe3O4@Cu nanocomposites could catalyze the degradation of organic dyes. The catalytic activities of the Fe3O4@Cu nanocomposites for the reduction of nitrophenol were also studied. The Fe3O4@Cu nanocomposites are more efficient catalysts compared with Cu nanoparticles and can easily be recovered from the reaction mixture with magnet. The cost effective and recyclable Fe3O4@Cu nanocomposites provide an exciting new material for environmental protection applications. © 2014 Elsevier B.V. All rights reserved.

Keywords: Magnetic materials Composite materials Nanostructures Metals

1. Introduction Owing to their excellent optical, mechanical and magnetic properties, magnetic nanoparticles have attracted considerable interest in the areas of magnetic storage media, ferrofluids, chemical catalysts, and biomedicine and technology (including bio-sensing, targeted drug delivery, and contrast agents in magnetic resonance imaging) [1e6]. Superparamagnetic iron oxide nanoparticles (Fe3O4) are the primary focus of magnetic nanoparticles because of their larger magnetic moments,

* Corresponding author. Fax: þ86 22 274 034 75. ** Corresponding author. E-mail address: [email protected] (M. Tang). http://dx.doi.org/10.1016/j.matchemphys.2014.08.029 0254-0584/© 2014 Elsevier B.V. All rights reserved.

excellent superparamagnetism, and high stability in aqueous media [7,8]. Monodispersed superparamagnetic Fe3O4 is generally synthesized in either aqueous or organic solutions and requires sophisticated surface modifications. The surface modification has three functions: to control the size and morphology of the magnetic nanoparticles, to improve their stability, and to functionalize the magnetic particles. Meanwhile, the modification should inhibit the Fe3O4 aggregation in both biological media and magnetic fields. The surface modification also determines the applications of the magnetic nanoparticles [9e12]. The modifier can be a monomeric stabilizer (like carboxylates, phosphates, and sulfates), a polymer (like dextran, polyethylene glycol, dendrimers and chitosan), an inorganic material (like silica), or liposomes [13e16].

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Fe3O4 nanoparticles have recently emerged as a conventional support material for catalysts, since they can be easily separated from the reaction system by manipulating the external magnetic field. Thus combining a magnetic material with a noble metal to fabricate a catalyst has generated new magnetically recyclable catalysts with good catalytic activities. For example, chemical methods have been developed to produce magnetically recyclable photocatalysts like, Fe3O4@C@Ag and Ag-coated Fe3O4@TiO2 [17,18]. Other magnetically recyclable catalysts that have been developed include, AueFe3O4 heterostructures for nitrophenol reduction [19], PdeFe3O4@C hybrids with high catalytic activity for Suzuki coupling reactions [20], Pt/Fe3O4 catalysts for the highly selective hydrogenation of o-chloronitrobenzene and m-chloronitrobenzene [21], and PteRu/Fe3O4/C nanoparticles for the selective hydrogenation of ortho-chloronitrobenzene [22]. In addition, upon exposure to visible light, Fe3O4@Ag nanocomposites have been found to be effective catalysts for the photodegradation of organic dyes (neutral red) with a degradation rate of 93.7% within 30 min [23]. They also have excellent catalytic activity, convenient magnetic separability, and long-term stability for the reduction of Rhodamine B in the presence of NaBH4 [24]. An efficient method for the alkoxycarbonylation of aryl iodides using magnetically recoverable Pd/Fe3O4 catalyst under an atmosphere of carbon monoxide has also been established [25]. This catalyst was completely recoverable simply by applying an external magnetic field, and the efficiency of the catalyst was unaltered even after five cycles. Further, AgeAu bimetallic nanocrystals supported on Fe3O4 composite microspheres have been shown to display high catalytic ability for the reduction of 4nitrophenol (4-NP) to 4-aminophenol (4-AP) [26]. The maximum reaction rate was 1580 s1 g1, which is far higher than those for monometallic composites. However, all of the above recyclable catalysts used noble metals which are expensive. Except these noble metals, some non-noble metallic nanoparticles were also assembled on Fe3O4 particles. For example, Cs/Al/Fe3O4 shows good performance on biodiesel fatty acids methyl ester (FAME) production [27]. Photomagnetic difunctional pine cone-like Fe3O4/ Cu2O/Cu porous nanocomposite displayed enhanced catalytic activity to the photodegradation of methyl orange compared with Cu2O/Fe3O4 [28]. Cu nanoparticles are cheap and easily fabricated compared to traditional catalysts. Kidwai et al. fabricated Cu nanoparticles that provide an efficient, economical, and novel way to synthesize diaryl ethers via an Ullmann-type coupling [29]. This synthetic method avoided the use of a heavy metal co-catalyst and gave diaryl ethers in satisfactory yields with applicability to a wide range of substrates. Bhadra et al. developed a convenient and efficient one-pot-three-component condensation for the synthesis of aryl and vinyl dithiocarbamates catalyzed by Cu nanoparticles in water [30]. Here, a facile route was developed for the preparation of catalytically active Fe3O4@Cu nanocomposites. The Fe3O4@Cu nanocomposites were characterized and their catalytic performance was tested using the reduction of organic dyes in aqueous solution under mild conditions. As we all known, the organic dyes can well dissolve in water or organic solvent and has been found to be potentially toxic, and the common method to eradicate the polluter is photodegradation by nanomaterials. In the experiment, it was found that the Fe3O4@Cu nanocomposites could catalyze the degradation of organic dyes in the presence of NaBH4. In addition, their performance for the reduction of 4-NP to 4-AP with NaBH4 was also investigated. These Fe3O4@Cu nanocomposites are expected to be a new class of highly efficient, fully renewable and ecofriendly heterogeneous catalysts which could be used in industrial applications.

2. Experimental section 2.1. Materials Ferric chloride hexahydrate (FeCl3$6H2O), ferrous chloride tetrahydrate (FeCl2$4H2O), ammonium hydroxide (NH3$H2O, 25%), copper sulfate pentahydrate (CuSO4$5H2O), methyl red (MR), methyl orange (MO), methyl blue (MB), and 4-NP were from Aladdin. L-Lysine (L-Lys) and borohydride (NaBH4, 98%) was purchased from Aldrich. All chemicals were analytical grade and used as received. 2.2. Preparation of Fe3O4 nanoparticles The Fe3O4 nanoparticles were prepared via a chemical coprecipitation method. In a typical procedure, 1.2 g of FeCl2$4H2O (6 mmol) and 2.7 g of FeCl3$6H2O (10 mmol) were dissolved in 50 mL of deionized water under the protection of an Ar atmosphere. Next, 40 mL of 25% ammonium hydroxide solution was diluted to 200 mL and then added dropwise to the above mixture with vigorous stirring. The mixture was then allowed to react for 30 min at room temperature to obtain a black precipitate that was subsequently isolated with the aid of a magnet. The recovered material was rinsed and centrifuged at 8000 rpm several times until the pH of the solution was 7. The wet Fe3O4 was dried at 50  C in a vacuum oven to obtain a black powder for further usage. 2.3. Preparation of Fe3O4@Cu nanocomposites The Fe3O4@Cu nanocomposite was prepared as follows: The prepared Fe3O4 nanoparticles (50 mg) were dispersed in 50 mL of deionized water and 0.5 g L-Lys was then added. The mixture was sonicated for 30 min, followed by the addition of 30 mL of CuSO4 solution (0.2 mmol L1). The solution was vigorously stirred for 30 min and then 0.6 g of NaBH4 was quickly added and the mixture was allowed to react for 1 h under rapid stirring. The product was separated magnetically and washed several times with deionized water to eliminate impurities. The product was then dispersed in 10 mL of deionized water. For comparison, Fe3O4@Cu magnetic nanoparticles (MNCs) were prepared from different CuSO4 concentrations (0.1, 0.2, 0.4, 0.8, and 1.6 mmol L1) which are denoted as MNCs-1, MNCs-2, MNCs-4, MNCs-8, and MNCs-16, respectively. 2.4. Characterization of samples Fourier transform infrared (FT-IR) spectra of the samples were measured with a PerkineElmer Paragon-1000 FT-IR spectrometer in the range of 500e4000 cm1. Each FT-IR spectrum was the average of 20 scans. The sample for transmission electron microscopy (TEM) were prepared by placing drops of a diluted Fe3O4@Cu aqueous suspension onto a carbon coated nickel grid, which was then dried under ambient conditions prior to being introduced into the TEM chamber. TEM observation and energy dispersive X-ray spectroscopy (EDX) measurements were performed using a Philips Tecnai G2F20 microscope at 200 kV. The amount of loaded metal on the catalysts was determined by inductively coupled plasma spectroscopy (ICP-9000 (N þ M), USA Thermo Jarrell-Ash Corp.). X-ray powder diffraction (XRD) analysis was conducted on a BDX3300 X-ray diffractometer at a scanning rate of 4 /min with 2q ranging from 10 to 90 , employing Cu Ka radiation (l ¼ 0.15418 nm). UVevis absorption spectra were recorded on a TU-1901 UVevis spectrometer using deionized water as the reference.

M. Tang et al. / Materials Chemistry and Physics 148 (2014) 639e647

The magnetic properties of the samples were investigated using a vibrating sample magnetometer (VSM; Model LDJ9500) with an applied field between 14,000 and 14,000 Oe at room temperature.

The catalytic activity of the Fe3O4@Cu nanocomposites was investigated using the reduction of dyes by NaBH4. For the catalytic reduction of dyes, fresh NaBH4 was mixed with an aqueous solution of methyl red (MR), methyl orange (MO) and methyl blue (MB) dye (2.5 mL, 20 mg L1). After the reaction, Fe3O4@Cu nanocomposites were collected by using an external magnetic field. The nanocomposites were washed two times with deionized water, and then reused. For the catalytic reduction of 4-NP, fresh NaBH4 was mixed with an aqueous solution of 4-NP (2.5 mL, 0.21 g L1, 1.499 mmol L1) to give an initial NaBH4 concentration of 1.316 mmol L1. After the solution changed from light yellow to deep yellow, the Fe3O4@Cu nanocomposites (1.0 mL) were added. Since the UV absorbance of 4-NP is linearly proportional to its concentration in the solution, the ratio of the absorbance at time t (At) to that at t ¼ 0 (A0) is equal to the concentration ratio ct/c0 of 4-NP. Consequently, the conversion progress can be directly measured using the absorption intensity. A TU-1901 spectrophotometer (Panaflo®, Japan) was employed to monitor the progress of the conversion of 4-NP to 4-AP at room temperature. 3. Results and discussion The synthetic scheme route for the Fe3O4@Cu nanocomposites is illustrated in Fig. 1. First, Fe3O4 nanoparticles with hydroxyl groups on their surfaces were modified with LeLys to introduce eNH2 groups which were then used to bind Cu2þ ions through Cu2þ eNH2 complex. The bound Cu2þ ions were then reduced to Cu with NaBH4 to form the Fe3O4@Cu nanocomposites. In order to confirm the successful modification of the Fe3O4 nanoparticles with the LeLys, FTIR spectra of LeLys and the LeLys modified Fe3O4 were measured and are shown in Fig. 2. These peaks centred at 1025, 1405, 1625, 3423 cm1 can be attributed to eCeN bond, eCeO vibration, eC]O stretching vibrations, and eNeH stretching vibrations, respectively [32]. The spectrum of the modified Fe3O4 has sharp band at about 582 cm-1 which correspond to the FeeO vibration peaks. The results indicate that LeLys

HO HO

OH

OH OH OH

HO HO HO

OH

L-Lys

Transimittance

2.5. Reduction of dyes and 4-NP catalyzed by the Fe3O4@Cu nanocomposites

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3423 N-H

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1405 1025 1625 C-O C-N C=O

Fe3O4-(L-Lys) 582 Fe-O

4000 3500 3000 2500 2000 1500 1000

500

-1 Wavenumber(cm ) Fig. 2. FTIR spectra of LeLys and LeLys modified Fe3O4 nanoparticles.

was successfully attached to the surface of the Fe3O4 spheres. The modification of the Fe3O4 nanoparticles with LeLys facilitates the attachment of metallic nanoparticles. To determine the crystallinity of the samples, X-ray diffraction patterns of Fe3O4 and Fe3O4@Cu were measured and are shown in Fig. 3. For Fe3O4, eight typical peaks were observed at 18.4 , 30.1, 35.4 , 43.2 , 53.4 , 57.2 , 62.5 , and 74.3 , which are due to the diffraction of the (111)，(220), (311)，(400)，(422), (511), (440), and (533) lattice planes of Fe3O4, respectively [31]. For Fe3O4@Cu, there is an addition peak at 50.40 from the (200) lattice plane of the metallic Cu nanoparticles [33,34]. The metal Cu nanoparticles speaks at 43.3 and 73.99 overlap with the 43.2 and 74.3 peaks of Fe3O4. The morphologies of Fe3O4, LeLys modified Fe3O4 and MNCs-2 were observed with TEM. The Fe3O4 nanoparticles and LeLys modified Fe3O4 nanoparticles are alike as shown in Fig. 4(a)e(b). The particles are all spherical with an average diameter of about 10 nm, but the LeLys modified Fe3O4 nanoparticles are more dispersed. The high-resolution TEM (HRTEM) image of the Fe3O4 nanoparticles in Fig. 4(c) clearly show lattice fringes with a lattice spacing of about 0.4812 nm which correspond to the (111) plane of a Fe3O4 crystal. The TEM images of the MNCs-2 are shown in Fig. 4(d)e(f). Fig. 4(e) shows that its surface was rougher than that of Fe3O4, and the small nanoparticles on the surfaces of the Fe3O4 nanoparticles are Cu nanoparticles with sizes of about 3 nm. The HRTEM image of the small particles in Fig. 4(f) clearly shows

NH2 O

L-Lys

NH2

Cu2+

O

H+

OH OH

NH2 O O

=

Fe3O4

L-Lys =

H2N

NaBH4

NH2

=

Cu2+

=

Cu Nanoparticals

COOH NH2

Fig. 1. Synthetic route for the Fe3O4@Cu nanocomposites.

Fig. 3. XRD Patterns of Fe3O4 and Fe3O4 @Cu nanocomposites.

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Fig. 4. TEM images of (a) Fe3O4, and (b) Fe3O4-(L-Lys); (c) HRTEM of Fe3O4; (d, e, f) TEM images of the MNCs-2; and (g) EDX spectrum of the MNCs-2.

lattice fringes with a lattice spacing of about 0.212 nm, which indexes to the (111) spacing of Cu crystal. In addition, the MNCs-2 is obtained with the aid of a magnet, so the Cu nanoparticles of MNCs-2 are formed around the Fe3O4, and the individual Cu

particles (if have) remain in the solution and are seperated from MNCs. The EDX spectrum of the MNCs-2 confirms that the particles contain Fe, O and Cu (Fig. 4(g)), and this further proved that Cu

M. Tang et al. / Materials Chemistry and Physics 148 (2014) 639e647

Magnetization(emu/g)

80 60

Fe O -(L-Lys) 3 4

40

Fe O 3 4

20

MNCs-2

0 -20 -40 -60 -80 -10000

-5000

0

5000

10000

Magnetic Field(Oe) Fig. 5. Magnetization curves of Fe3O4, L-Lys modified Fe3O4 and MNCs-2 at 300 K.

nanoparticles have attached to the surface of the Fe3O4 nanoparticles. Thus, it can be recongnized that the Cu nanoparticles were attached to the surface of the Fe3O4 spheres. To further examine the actual amounts of Cu in the MNCs, ICP was used for elemental analysis. According to the ICP test results, the amount of Cu in MNCs-1, MNCs-2, MNCs-4, MNCs-8 and MNCs-16 were 0.31%, 0.62%, 1.22%, 2.41%, and 4.75%, respectively, which are all close to the theoretical loading of Cu. Fig. 5 shows the magnetic hysteresis curves of the Fe3O4, the LeLys modified Fe3O4, and the Fe3O4@Cu measured at 300 K. They all display high saturation magnetization. The magnetic saturation value (Ms) of the Fe3O4 nanoparticles was 75.23 emug1. After modification with LeLys, the Ms decreased to 62.25 emug1 and that of the MNCs-2 was 60.11 emug1. In a

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word, the saturation magnetization of magnetic microspheres decreased gradually due to the decrease of Fe3O4 content in the composite microspheres. Although the Ms of MNCs-2 microspheres is lower compared with the original magnetic Fe3O4, it is still in the superparamagnetic range which makes the composite microspheres be separated rapidly from the solution under the magnetic field. The reduction of dye is used to determine the catalytic activity of metal nanoparticle [35]. So, the reduction of MR, MO and MB in distilled water in the presence of NaBH4 with MNCs-2 as catalyst was explored. The freshly prepared aqueous MR solution is red (Fig. 6(a1)) with an absorbance peak maximum at 535 nm. When NaBH4 was added, the absorbance intensity shift to 435 nm (Fig. 6(b)) in the alkaline condition, and the color of the solution changed to yellow (Fig. 6(a2)). The reduction of MR can be achieved in the presence of NaBH4 without using any catalyst, but it requires about 38 min. After MNCs-2 was added, the absorbance intensity at 435 nm completely disappeared within 120 s (Fig. 6(c)), and the solution became colorless after the MNCs-2 was removed by a magnet (Fig. 6(a4)). Similarly, the catalytic activity of MNCs-2 for the reduction of MO and MB was also explored and the results are shown in Fig. 7. In the presence of MNCs-2, it required 12 s and 45 s to completely reduce MO and MB respectively, whereas it took 83 and 56 min to reduce MO and MB in the absence of MNCs-2. This dates indicate that the Fe3O4@Cu nanocomposites possess high catalytic activities for the degradation of dyes. An aqueous solution of 4-NP has an absorbance peak at 317 nm. After the addition of NaBH4, the peak immediately red-shifts to 400 nm due to formation of the stronger conjugate action resulted from the 4-nitrophenolate ion, and the solution color changes from pale yellow to yellow (Fig. 8(a)). When MNCs-2 were added, the

Fig. 6. (a)Photographs and (b)UV/Vis absorption spectra of MR before and after reduction catalyzed by MNCs-2; (c)Time-dependent UV/Vis absorption spectra for the reduction of MR.

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1.8

a

1.4

1.6

MO MO+NaBH4

1.2

After degradation

1.0 A bs

b

1.4

0.8 0.6 0.4 0.2

A bsorbance

1.6

0s 3s 6s 9s 12s

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0.0

0.0

-0.2

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300

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500

600

700

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800

350

400

450

500

550

600

Wavelength(nm)

Wavelength (nm) 3.0

c

2.0

MB MB+NaBH4

2.0

After reduction

A b sorbance

A bsorbance

2.5

1.5 1.0 0.5 0.0

d

1.5

0s 20s 30s 45s

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0.0

200

300

400

500

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800

Wavelength (nm)

500

550

600

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700

750

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Wavelength(nm)

Fig. 7. UV/Vis absorption spectra of (a)MO and (c)MB before and after reduction catalyzed by MNCs-2; Time-dependent UV/Vis absorption spectra for the reduction of (b) MO and (d) MB with MNCs-2.

a

1.6 1.4

b

4-NP 4-NP+ NaBH4

Absorbance

1.2 1.0

After Reduction 317

400

0.8 0.6 0.4

304

0.2 0.0 250

300

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400

450

500

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Wavelength (nm) Fig. 8. (a) Photographs and (b) UV/Vis absorption spectra of 4-NP before and after reduction catalyzed by MNCs-2.

intensity of absorption peak at 400 nm decreased, and at the same time, a new absorption peak for 4-AP appeared at 304 nm (Fig. 8(b)). The UVevis spectra show an isosbestic point for the two absorption bands, indicating that the nitro compound was gradually converted to aminophenol without any side reactions [36,37]. After completion of the reaction, the peak at 400 nm was completely gone. Fig. 9(a) shows the typical evolution of the UVevis spectra during the reduction with MNCs-2 catalyst. The reaction was complete in 65 s. The reaction kinetics can be easily monitored from the time-dependent absorption spectra. The concentration of NaBH4 is very high compared with that of 4-NP. This is done, because excess NaBH4 can increase the pH of the system which retards the degradation of the BH 4 [38]. In addition, the liberated hydrogen cleanses the air from the solution thereby preventing the oxidation of 4-AP by the air. Since NaBH4 was in excess, the reaction can be assumed to follow pseudo-first order reaction kinetics [39]. Thus, the pseudo-first order rate constant of the reaction K can be calculated from the equation ln (At/A0) ¼ Kt, where A0 and At are the absorbance values of 4-NP initially and at time, respectively. The plot of ln (At/A0) versus time s is linear in the presence of the MNCs-2, as shown in Fig. 9(b). The rate constant calculated from the slope of the plot is 0.04574 s1. In order to compare these results with others reported in the literature, the ratio of the rate constant K to the total weight of the catalyst (0.036 mg) was calculated, k ¼ K/m (k ¼ 0.04574 s1/0.036 mg ¼ 1.27  103 s1 g1), which is called the activity factor. The activity factor was higher than that for porous Cu microspheres (88 s1 g1) and 9.5 nm Cu cubes (105 s1 g1) [40,41]. These results also show that Fe3O4@Cu has good catalytic performance compared with noble metal catalysts, such as AgNPs/SNTs-4(142 s1 g1) [42], and Au/grapheme

M. Tang et al. / Materials Chemistry and Physics 148 (2014) 639e647

645

1.6 1.4

e

0min 3min 6min 9min 12min 15min 18min

Absorbance

1.2 1.0 0.8 0.6 0.4 0.2 0.0 250

300

350

400

450

500

Wavelength (nm) Fig. 9. (a) Time-dependent UV/Vis absorption spectra for the reduction of 4-nitrophenol with MNCs-2; (b) The plot of absorbance at 400 nm versus the reduction time, (c) Timedependent UV/Vis absorption spectra for the reduction of 4-nitrophenol with none, (d) Fe3O4 nanoparticles, and (e) Cu nanoparticles.

hydrogel (132 s1 g1) [43], but Fe3O4@Cu would be a much cheaper raw material. In addition, catalytic activity of the Fe3O4@Cu nanoparticles is also better than those of the hydrogel catalysts in 4-NP reduction [44e47]. To identify the catalytic center, the reduction of 4-NP was conducted with no catalysts, with Fe3O4 nanoparticles and with Cu nanoparticles. As seen in Fig. 9(c) the reduction of 4-NP to 4-AP can be achieved in the presence of NaBH4 without using any catalyst, but it requires about 300 min. In the same condition, it requires 64 min to finish the reaction in the presence of Fe3O4 (Fig. 9(d)). When the same amount of Cu nanoparticles were added, it only took 18 min to finish the reaction (Fig. 9(e)). Therefore, the Fe3O4 can acts as the support and stabilizing agent to prevent the aggregation of the Cu nanoparticles and improves their catalytic activity. In order to explore the amount of Cu nanoparticles to the catalytic activity, Fe3O4@Cu magnetic nanoparticles were prepared from different CuSO4 concentrations were used as the catalysts. The catalytic activity of these MNCs is shown in Fig. 10(a). The activity

factors of those catalysts were in the order: MNCs-1
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M. Tang et al. / Materials Chemistry and Physics 148 (2014) 639e647

Fig. 10. (a) The catalytic activity of the different catalysts; (b) TEM image and (c) EDX spectrum of the MNCs-16.

Acknowledgment MNCs-16

) Conversion (%

98 MNCs-8

97

MNCs-4

96

MNCs-1 MNCs-2

95 94 4

8

le yc C

12

es tim

10

2

6

0

Fig. 11. Recycling of Fe3O4@Cu for the reduction reaction of 4-NP by NaBH4.

4. Conclusion A facile and efficient approach has been developed to synthesize Fe3O4@Cu nanocomposites using L-Lys as a linker. The Fe3O4@Cu displayed high catalytic activity for the degradation of organic dye. The prepared Fe3O4@Cu exhibited enhanced performance for the reduction of 4-NP compared to pure Cu nanoparticles because Fe3O4 acted as a support and stabilizing agent to effectively prevent aggregation of the Cu nanoparticles. The Fe3O4@Cu made from a high concentration of CuSO4 had the highest catalytic activity. The Fe3O4@Cu is magnetically separable and displayed a high catalytic activity after 13 cycles. The cost effective and recyclable Fe3O4@Cu nanocomposites provide an exciting new material for use in environmental protection applications.

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