Elsevier

Powder Technology

Volume 207, Issues 1–3, 15 February 2011, Pages 42-46
Powder Technology

In situ synthesis of hematite nanoparticles using a low-temperature microemulsion method

https://doi.org/10.1016/j.powtec.2010.10.008Get rights and content

Abstract

A novel microemulsion method is described for the in situ synthesis of α-Fe2O3 nanoparticles with ferrihydrite as a precursor and trace Fe (II) as a catalyst. The final products are characterized by XRD and TEM techniques. The influence of various factors on the transformation from ferrihydrite to hematite nanoparticles is investigated. The effects of ω (ω = nH2O / nCTAB) and weight ratio of CTAB to n-octane on the size of α-Fe2O3 nanoparticles are also studied, respectively.

Graphical Abstract

A novel microemulsion method is described for the in situ synthesis of α-Fe2O3 nanoparticles with ferrihydrite as a precursor and trace Fe (II) as a catalyst which does not require any calcination step. The nanoparticles were characterized by X-ray diffractometer (XRD) and transmission electron microscopy (TEM). It was found that the size of α-Fe2O3 nanoparticles was influenced by ω (ω = nH2O / nCTAB) and weight ratio of CTAB to n-octane.

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Introduction

Hematite (α-Fe2O3), which is the most stable iron oxide under ambient conditions, has attracted an increasing interest in the fields of nanoscience and nanotechnology because of its potential applications in pigments [1], gas sensors [2], field effect transistor [3], photoelectrolysis reactors [4], [5], contrast reagents/drug delivery [6], magnetic storages [7], photoanode for possible photo-electrochemical cell [8], catalysts [9], and so on. It is well known that the morphology and size of α-Fe2O3 have a great impact on their chemical and physical properties [10]. In order to control particle sizes and obtain narrow distributed and monodispersed nanoparticles, various strategies have been employed [11]. Microemulsions have been widely used since they can provide controllable “micro-reactors” (surfactant-covered water pools) that limit particle growth and agglomeration and render particle sizes in the nm scale [12]. As a result, the particles obtained in microemulsion systems are generally very fine and monodispersed. For example, Bumajdad's group has achieved successfully α-Fe2O3 nanoparticles by a microemulsion method [13]. However, microemulsion method usually involves synthesizing a precursor gel of iron, followed by further high-temperature calcinations to form the oxide with crystallinity.

In this paper, a low-temperature microemulsion method has been employed to synthesize directly α-Fe2O3 nanoparticles with trace Fe (II) as a catalyst. This procedure is different from the reported methods of microemulsion in literatures without any requirement of calcination step at high temperature (e.g., 400 °C) [13]. Moreover, the novel method could maintain a great many of advantages, such as simple equipment, homogeneous grain size distribution, lower agglomeration etc.

Section snippets

Experimental

Analytical grade reagents (hexadecyl trimethyl ammonium bromide, n-octane, n-butanol, ferric chloride hexahydrate FeCl3·6H2O and sodium hydroxide NaOH) and distilled water were used in all experiments.

Hexadecyl trimethyl ammonium bromide, n-butanol and n-octane were used as surfactant, cosurfactant and oil phase, respectively. The surfactant, cosurfactant and oil phase with the weight ratio 1:0.8:2.83 were mixed and then a certain volume of mixture solution of FeCl2 and FeCl3 was added. The

The catalysis of Fe (II) on the transformation of ferrihydrite in microemulsion

Ferrihydrite prepared in microemulsion system at pH 7 was heated and refluxed for 10 h or 4.5 h in the absence or presence of trace amounts of Fe (II) ions. XRD patterns of the samples are shown in Fig. 1. It can be seen in Fig. 1 that ferrihydrite has transformed into α-Fe2O3 in the presence of trace amounts of Fe (II) ions (Fig. 1b), while no detectable change is found when ferrihydrite is heated and refluxed for 10 h in the absence of trace amounts of Fe(II) ions(Fig. 1a). All the peaks in

Conclusion

Nanosized hematite particles can be directly synthesized by a simple microemulsion method without any requirement of calcination step at high temperature. The size of hematite particles can be controlled by regulating ω value or the weight ratio of surfactant to n-octane. The particle size increases with the increase of ω value, and increasing the weight ratio of surfactant to n-octane is beneficial to prepare smaller α-Fe2O3 nanoparticles.

Acknowledgments

This work was supported by a grant from the Natural Science Foundation of Hebei Province (E2006000167).

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