Chinese Chemical Letters 24 (2013) 341–343

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Chinese Chemical Letters

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Original article

b-Cyclodextrin assisted one-pot synthesis of mesoporous magnetic Fe3O4@C andtheir excellent performance for the removal of Cr (VI) from aqueous solutions

Hui Zhang a,b,*, De-Lei Liu b, Li-Li Zeng c, Meng Li b

a State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, Chinab School of Chemistry and Chemical Engineering, Southwest Petroleum University, Chengdu 610500, Chinac Dushanzi Petrochemica Company, Dushanzi District, Karamay 833600, China

A R T I C L E I N F O

Article history:

Received 18 December 2012

Received in revised form 24 January 2013

Accepted 2 February 2013

Available online 14 March 2013

Keywords:

Mesoporous magnetic Fe3O4@C

Nanospheres

Adsorbents

A B S T R A C T

Mesoporous magnetic Fe3O4@C nanoparticles have been synthesized by a one-pot approach and used as

adsorbents for removal of Cr (IV) from aqueous solution. Magnetic iron oxide nanostructured materials

encapsulated by carbon were characterized by scanning electron microscope (SEM), nitrogen adsorption

and desorption, X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The

adsorption performance of the nanomaterial adsorbents is tested with the removal of Cr (IV) from

aqueous solution. The results reveal that the mesoporous magnetic Fe3O4@C nanospheres exhibit

excellent adsorption efficiency and be easily isolated by an external magnetic field. In comparison with

magnetic Fe3O4 nanospheres, the mesoporous magnetic Fe3O4@C exhibited 1.8 times higher removal

rate of Cr (VI). The mesoporous structure and an abundance of hydroxy groups on the carbon surface may

be responsible for high absorbent capability.

� 2013 Hui Zhang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

1. Introduction

Carbon-encapsulated Fe3O4 magnetic nanoparticles recentlyhave attracted more and more attention in water purification dueto their high magnetic separation efficiency, mild operating condi-tions and potentially facile, specific functional modifications [1–4].Various approaches for synthesizing magnetic Fe3O4 nanoparti-cles have been reported in the literature [5–7]. However, most ofthese methods involve a two-step hydrothermal assembly toprepare the Fe3O4 nanoparticles. Magnetic Fe3O4 particles, astemplate, are first prepared by various chemical route methods,and then the magnetic template is further encapsulated via acarbon source.

b-Cyclodextrin (b-CD) is a cyclic oligosaccharide containingseven glucopyranose units. This cyclic orientation possesses atruncated cone structure with hydrophilic rim and lipophilic interiorgroups. This special structure is more facile to prepare carbon coatedFe3O4 nanoparticles via the carbonization process. Herein, a one-potsynthesis approach and b-CD, as the carbon source, are employed toprepared magnetic Fe3O4@C nanomaterials.

* Corresponding author at: State Key Laboratory of Oil and Gas Reservoir Geology

and Exploitation; School of Chemistry and Chemical Engineering, Southwest

Petroleum University, Chengdu 610500, China.

E-mail address: zhanghuiswpu@163.com (H. Zhang).

1001-8417/$ – see front matter � 2013 Hui Zhang. Published by Elsevier B.V. on beha

http://dx.doi.org/10.1016/j.cclet.2013.02.007

2. Experimental

The one-step synthesis route for preparation of Fe3O4@Cnanospheres employed in this study is a modified procedurereported elsewhere [6]. In a typical experiment, the desiredamount of FeCl3�6H2O was dissolved in 30 mL of ethylene glycol(EG) to generate a clear solution. Then 2.5 mmol urea, 0.5 mmol b-CD and an amount of formaldehyde were added into the abovesolution and vigorously stirred for 45 min to form a homogeneoussolution. Finally, the mixture was transferred into a Teflon-linedstainless steel autoclave at 200 8C for 24 h. The synthesis approachis shown in Scheme 1. For comparison purposes, magnetic Fe3O4

nanospheres were also prepared by the similar procedure withoutthe addition of b-CD and formaldehyde.

3. Results and discussion

SEM images of Fe3O4 and Fe3O4@C nanoparticles are displayedin Fig. 1. The synthesized Fe3O4 and mesoporous Fe3O4@Cnanomaterials with spherical shapes are uniformly very welldispersed.

The surface groups of the prepared mesoporous Fe3O4@Cnanoparticles are further analyzed by FTIR (see Fig. 2). The FT-IRspectrum exhibits stretching vibrations of hydroxyl groups at3418 cm�1 and the Fe–O bond vibrations of the Fe3O4 at 587 cm�1,indicating there are carbonaceous coatings and hydroxy groups on

lf of Chinese Chemical Society. All rights reserved.

[(Fig._1)TD$FIG]

Fig. 1. SEM images of Fe3O4 (a and b) and Fe3O4@C (c and d) nanospheres.

[(Scheme_1)TD$FIG]

Scheme 1. One-pot approach for mesoporous magnetic Fe3O4@C nanospheres.[(Fig._2)TD$FIG]

Fig. 2. FT-IR spectra of the magnetic nanoparticles: (a) Fe3O4 and (b) Fe3O4@C.

H. Zhang et al. / Chinese Chemical Letters 24 (2013) 341–343342

the surface of Fe3O4 [2]. This effect is beneficial by providingexcellent hydrophilic properties of Fe3O4 in aqueous solution. Thedistribution of the iron oxide and carbon in the sample indicated byFTIR is in good agreement with values reported for Fe3O4 in theliterature [8].

Fig. 3 depicts XRD patterns of the magnetic Fe3O4 and Fe3O4@Cparticles. The patterns are almost identical for Fe3O4 and Fe3O4@C,both exhibiting the (2 2 0), (3 1 1), (4 0 0), (4 2 2) and (4 4 0)diffraction peaks which are characteristic peaks of Fe3O4 (JCPDS #65-3107). The weak and broad peaks of Fe3O4@C, at the lower 2udegrees, could be attributed to the amorphous carbon coating onthe Fe3O4 particles [9]. Calculations using Scherer’s equation andthe 311 (2u = 35.4) diffraction line yielded crystallites of about36 nm and 14 nm for Fe3O4 and Fe3O4@C, respectively.

[(Fig._3)TD$FIG]

Fig. 3. XRD patterns of the magnetic nanoparticles: (a) Fe3O4 and (b) Fe3O4@C.

[(Fig._4)TD$FIG]

Fig. 4. Nitrogen adsorption–desorption of magnetic Fe3O4@C nanoparticles: (a) isobars and (b) pore size distribution.

[(Fig._5)TD$FIG]

Fig. 5. The effect of contact time on the adsorption of Cr (VI) to Fe3O4@C and Fe3O4

nanomaterials.

H. Zhang et al. / Chinese Chemical Letters 24 (2013) 341–343 343

Fig. 4 displays the texture structure of prepared Fe3O4@Cnanospheres by nitrogen adsorption and desorption. The isobarsand the pore size distribution of Fe3O4@C nanospheres werecalculated using BJH method. As can be seen, the isobars and poresize distribution suggest that Fe3O4@C nanospheres are porousstructures with average pore size 6.2 nm.

Cr (IV) removal experiments were carried out by adsorbing Cr(IV) from aqueous solutions at 28 8C and pH 7.6. Firstly, thenanospheres were dispersed in the Cr (IV) solution, and then after150 min, the magnetic materials were attracted and separated byan external magnet. The Cr (IV) removal rate was calculated byfollowing formula:

%removal ¼ c0 � ct

c0� 100

where c0 and ct (mg/mL) are the concentrations of Cr (IV) in thesolution at initial and equilibrium time, respectively.

Fig. 5 shows the influence of contact time on the removal rate ofCr (VI). The initial concentration of Cr (VI) ions was 507 mg/mL. TheCr (IV) adsorption increases with the increase of exposure time. At150 min (2.5 h) contact time, the removal of Cr (IV) by Fe3O4@Cattained 92.4%; while for the Fe3O4 nanoparticles, the removal rateof Cr (VI) is only 19.7%.

4. Conclusion

In summary, mesoporous magnetic Fe3O4@C nanospheres withaverage pore size of 6.2 nm were prepared by the one-pot,solvothermal method for removal of Cr (IV) from water. Theprepared mesoporous magnetic nanospheres can be well dispersedin the aqueous solution and easily separated from the solution byusing an external magnet. The removal rate of Cr (IV) from water isup to 92.4%, which is much higher than by magnetic Fe3O4

nanospheres. The excellent adsorption capacity could be attributedto the mesoporous and an abundance of surface hydroxy groups ofFe3O4@C. Mesoporous carbon encapsulated magnetic Fe3O4

nanoparticles would be an excellent environment friendly adsor-bent for the removal of pollutants in the field of wastewatertreatment.

Acknowledgments

This work was supported by the Open Fund of State KeyLaboratory of Oil and Gas Reservoir Geology and Exploitation (No.PLN1132) in China, Scientific Research Fund of Sichuan ProvincialEducation Department and Scientific Research Foundation of theSouthwest Petroleum University of China.

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