Elsevier

Materials Research Bulletin

Volume 43, Issues 8–9, 4 August–4 September 2008, Pages 2457-2468
Materials Research Bulletin

Preparation, characterization and application of Fe3O4/ZnO core/shell magnetic nanoparticles

https://doi.org/10.1016/j.materresbull.2007.07.035Get rights and content

Abstract

Fe3O4 magnetic nanoparticles (MNPs) were synthesized by a co-precipitation method. The phase purity was confirmed by X-ray powder diffraction (XRD) analysis. The crystal size was found to be 10 nm from transmission electron microscopy (TEM). It is evidenced that the surface of Fe3O4 MNPs was modified by sodium citrate. The Fe3O4/ZnO core/shell MNPs were obtained by coating the MNPs with direct precipitation using zinc acetate and ammonium carbonate. The precursor was firstly dried and then calcined at 350 °C. The antioxidation tests indicated that the core/shell MNPs give better antioxidation than that of the Fe3O4 MNPs. The photocatalytic degradation of methyl orange revealed that the core/shell MNPs have higher photocatalytic activity than that of the ZnO nanoparticles. Separation of the core/shell MNPs from the aqueous suspension using a magnet provides an easy way to recycle the core/shell MNPs. After four-time recycling, the photocatalytic degradation percentage of the core/shell MNPs is about 70%.

Introduction

Nanoparticles have been widely used in optical, resonant, electrical and magnetic fields, etc. Various chemical methods have been used for the production of nanoparticles with narrow size distribution such as microemulsion method, electrospray pyrolysis and hydrothermal methods [1], [2], [3], [4], [5].

Nanosized Fe3O4 (as magnetite), is an important member of spinel type ferrite, and has been widely used in mineral separation [6], heat transfer applications [7], electrophotography [8], efficient hyperthermia for cancer removal [9], orientation control and directional transportation [10]. Methods about synthesis, characterization and application of Fe3O4 magnetic nanoparticles (MNPs) have been reported in the literature [11], [12], [13], [14], [15], [16].

The nanosized ZnO has great potentiality for being used in preparing gas sensors [17], [18], [19], chemical absorbent [20], [21], varistors [22], [23], electrical and optical devices [24], [25], [26], electrostatic dissipative coating [27], catalysts for liquid phase hydrogenation [28], and catalysts for photocatalytic degradation [29], [30], [31]. Hence, investigations on the synthesis and modification of nanosized ZnO have attracted tremendous attentions. A variety of methods have been reported in the literature for ZnO nanoparticle synthesis, including sol–gel technique [32], microemulsion synthesis [23], mechanochemical processing [33], spray pyrolysis and drying [31], thermal decomposition of organic precursor [34], RF plasma synthesis [35], low temperature synthesis [36], self-assembling [37], hydrothermal processing [38], vapor transport process [39], sonochemical or microwave-assisted synthesis [40], direct precipitation [41] and homogeneous precipitation [42].

Although the ZnO nanoparticles have been used as a catalyst for photocatalytic degradation, the Fe3O4/ZnO core/shell MNPs have not been sufficiently investigated. In the present investigation, a new Fe3O4/ZnO core/shell composite catalyst was synthesized to combine both advantages of Fe3O4 and ZnO. Fe3O4 MNPs were synthesized by the co-precipitation of Fe3+ and Fe2+. Then, the MNPs were dispersed in the deionized water using the sodium citrate. After this procedure, the basic zinc carbonate was coated onto the Fe3O4 MNPs by the direct precipitation with the zinc acetate and the ammonium carbonate. The obtained solids were firstly dried and then calcined to obtain Fe3O4/ZnO core/shell composite MNPs. Finally, ferrofluid (FF) was prepared by ball milling using the as-prepared core/shell composite MNPs.

Section snippets

Materials

Ferric chloride (FeCl3·6H2O), ferrous sulfate (FeSO4·7H2O), hydrazine hydrate (N2H4·H2O), zinc acetate (ZnAC2·2H2O), ammonium carbonate ((NH4)2CO3), aqueous ammonia (NH3·H2O) and methyl orange used are all analytic grade. Sodium citrate, acetone and ethanol are all chemical grade. Ar is industrial grade. Deionized water was used throughout the experiments.

Synthesis of Fe3O4 MNPs

Synthesis of the Fe3O4 MNPs was based on our previous study [43], [44], in which a solution of mixture of FeCl3 (0.5 M) and FeSO4 (0.5 M) with

XRD pattern

The X-ray powder diffraction patterns of the as-prepared Fe3O4, modified Fe3O4, ZnO, and Fe3O4/ZnO core/shell nanoparticles are, respectively, shown in Fig. 2a–d. Fig. 2a is the spectrum of Fe3O4 MNPs prepared by co-precipitation. The peaks agree with the standard Fe3O4 (cubic phase) XRD spectrum. The crystallographic parameters calculated using a soft provided by Panalytical company (Holland) are: a = b = c = 8.3740 Å, α = β = γ = 90.0000°, they are indexed to the cubic spinel phase of Fe3O4. The average

Conclusions

  • (1)

    The inverse cubic spinel phase of Fe3O4 MNPs with a diameter of around 10 nm was synthesized, and the saturation magnetization (Ms) is 67.78 emu/g. The Fe3O4/ZnO core/shell MNPs of Samples 2–6 were synthesized by a direct precipitation using zinc acetate and ammonium carbonate. The saturation magnetization (Ms) of composite MNPs can be 20.33 emu/g under optimal conditions.

  • (2)

    The Fe3O4 MNPs, which were treated by sodium citrate, showed better dispersion and could be coated by ZnO uniformly. The Fe3O4

Acknowledgments

The project was supported by the National Natural Science Foundation of China (NNSFC, No. 20476065), the Scientific Research Foundation for ROCS of State Education Ministry (SRF for ROCS, SEM), the Key Lab. of Multiphase Reaction of the Chinese Academy of Sciences (No. 2003-5), the State Key Lab. of Coal Conversion of CAS, the Key Lab. of Organic Synthesis of Jiangsu Prov., Foundation of Chemical Experiment Center of Soochow Univ. and R&D Foundation of Nanjing Medical Univ. (NY0586).

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