Hydrothermal synthesis and characterization of α-FeOOH and α-Fe2O3 uniform nanocrystallines

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Abstract

Inorganic nanoparticles with controlled size and shape are technologically important due to the strong correlation between these parameters and magnetic, electrical, and catalytic properties. Herein we demonstrated that under appropriate conditions, rodlike α-FeOOH (goethite) and porous fusiform α-Fe2O3 (hematite) uniform nanocrystallines could be selectively synthesized in large quantities via a facile surfactant sodium dodecyl sulfate (SDS) assisted hydrothermal synthetic route. The morphology and structure of the final products were investigated in detail by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and selected area electron diffraction (SAED). The probable formation mechanism of the α-FeOOH and α-Fe2O3 uniform nanoparticles was discussed on the basis of the experimental results.

Introduction

Over the past decades, inorganic nanoparticles with controlled size and shape have attracted vast attention because of their size and shape-dependent properties and great potential applications. Considerable effort has been devoted to the design and controlled fabrication of inorganic materials with controlled size and shape. Various synthetic methods are continually being improved to this end. Recently a variety of novel shapes such as tubes [1], rods [2], wire [3], belts [4], prisms [5], and cubes [6] have been reported through chemical reactions of precursors at room or slightly elevated temperatures. However, with the growing interest in building advanced materials using nanoscale building blocks, it remain a challenge to find simple and mild routes to control the parameters of final products to fine-tune their properties.

Iron oxides have attracted enormous attention owing to their interesting electrical [7], magnetic [8], and catalytic [9] properties and wide variety of potential applications in various fields such as electro-optic materials [10], sorbents [11], pigments [12], ion exchangers [13], and magnetic resonance imaging (MRI) [14], particularly in the field of catalysis [15]. Amongst the readily available carbon monoxide oxidation catalysts, iron oxide-based materials have been found to be especially attractive candidates as cheap and efficient catalysts [16]. Various procedures including wet chemical [17], [18], [19], [20], electrochemical [21], thermal decomposition techniques [22], and chemical oxidation in polymer [23] have been successfully employed for the synthesis of iron oxides nanocrystallines. As is well known, the properties of iron oxides nanocrystallines sensitively depend on their size and shape. In order to improve the functional properties such as catalytic activity, it is significant challenge to control the size and shape of iron oxides nanocrystallines. Porous iron oxides nanoparticles may provide some immediate advantages over their solid counterparts because of their relatively low densities and large surface areas for their applications. In recent years, Ocaña and co-workers have synthesized uniform iron oxides nanoparticles via aerial oxidation and forced hydrolysis methods [24], however, the products of such synthesis often involved complicated process or produced in low quantities.

In this paper, we demonstrated that rodlike goethite (α-FeOOH) and porous fusiform hematite (α-Fe2O3) iron oxide uniform nanocrystallines could be selectively synthesized through a facile hydrothermal synthetic route in large quantities under mild conditions. When only prolonging the hydrothermal time from 12 to 24 h, the rodlike α-FeOOH nanocrystallines could be transfered to porous fusiform α-Fe2O3 nanocrystallines. In this synthetic system, surfactant sodium dodecyl sulfate (SDS) was used as a structure-directing agent, and simple compounds of the hydrated ferrous chloride and sodium borohydride as reactants directly. The high yields, simple reaction apparatus and low reaction temperature give this novel method a good prospect in the future applications.

Section snippets

Experimental

All chemicals in this work, such as hydrated ferrous chloride (FeCl2·4H2O), sodium borohydride (NaBH4), and sodium dodecyl sulfate (SDS) were of analytical grade, and which were used without further purification.

Results and discussion

Fig. 1 shows typical X-ray diffraction (XRD) patterns (2θ scan) of the goethite (α-FeOOH) iron oxide nanocrystallines obtained at 140 °C for different reaction time. All the reflections of the XRD pattern can be finely indexed to an orthorhombic phase [space group: Pbnm(62)] of α-FeOOH with cell parameters a = 4.64 Å, b = 10.0, c = 3.03 Å (JCPDS file Card, No. 03-0249). The XRD patterns of Fig. 1 from a to c correspond to the goethite (α-FeOOH) iron oxide nanocrystallines obtained for 4, 8, and 12 h,

Conclusion

In summary, we have successfully synthesized the rodlike goethite (α-FeOOH) and porous fusiform hematite (α-Fe2O3) iron oxide uniform nanocrystallines via a facile surfactant sodium dodecyl sulfate assisted hydrothermal synthetic route at mild conditions. The influence of reaction time on size and shape was investigated. Results show the hydrothermal time was dominant. When maintained at 140 °C for 4 h, the sample of goethite (α-FeOOH) iron oxide is poorly crystallized, however, the sample of

Acknowledgements

Financial support of this work by National Natural Science Foundation of China (Grant no. 50504017) and Hunan Provincial Natural Science Foundation of China (Grant no. 05JJ30104) is gratefully acknowledged.

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