Synthesis of core–shell α-Fe2O3 hollow micro-spheres by a simple two-step process
Introduction
During the past few years, considerable researches have been done on the synthesis of core–shell structure materials with desired compositions due to their wide potential applications in biotechnology, optical, electronic, magnetic, catalytic and sensing devices [1], [2], [3], [4], [5], [6], [7]. However, the synthesized core–shell structures were usually of different components of core and shell. To the best of our knowledge, merely Fe3O4 homogeneous core–shell polyhedrons have been fabricated by a cetyltrimethyl ammonium bromide (CTAB) aided hydrothermal method [8]. The as-synthesized products are of super low saturation magnetization of 38.5 emu/g and negligible coercivity, which is evidently different from other Fe3O4 nanostructures and morphologies. Therefore, we are interested in developing simple method to synthesize homogeneous core–shell structures and research.
As one of the most important, non-toxic, nature-friendly, corrosion-resistant and stable metal oxide, hematite (α-Fe2O3) has become a very attractive material due to its wide applications such as battery, catalysis, gas sensor and pigments. Many techniques including vapor–solid growth [9], template aimed synthesis [10], sol–gel process [11], and hydrothermal synthesis [12] were employed to prepare α-Fe2O3 crystals. Different morphologies of α-Fe2O3 such as nanorods [13], nanowires [14], nanocubics [15], airplane-like structures [16], houseleek-like and snowflake-like dendrites [17], and hollow spheres [18], [19] have been fabricated by now. However, to the best of our knowledge, homogeneous core–shell sphere has not been reported by now. In this paper, an improved surfactant aided hydrothermal approach based on carbonization of glucose is reported to synthesize novel homogeneous core–shell α-Fe2O3 hollow spheres [20]. During the hydrothermal process, both the surfactant and the tuned temperature play crucial roles in the formation of core–shell structure.
Section snippets
Experimental
All the chemicals were analytical grade and purchased from Shanghai Chemical Reagents.
Results and discussion
SEM and TEM images of the products obtained from hydrothermal reaction were shown in Fig. 1. Fig. 1a is a SEM image of the products, which consist of large quantity of flake-based urchin-like architectural spheres. Those spheres are of mean size of about 1.2 μm with standard deviation ±0.4 μm. More clearly urchin-like architecture is shown in TEM image (Fig. 1b). It is found that the core of the urchin-like sphere is so big that near 1.2 μm and the flakes outside the core are of length less than
Conclusions
In conclusion, we have synthesized novel homogeneous Fe2O3 hollow micro-spheres with core–shell structures by a surfactant aided hydrothermal method. This novel structure has widely promising applications such as micro-reactor, delivery vehicle system and micro-stirrer due to its room temperature magnetism. Furthermore, the possible growth mechanism was suggested on the basis of experiment results. As the suggested formation mechanism is clear and in agreement with experiment results and the
Acknowledgement
We gratefully acknowledge the financial support from the Teaching and Research Award Program for Outstanding Young Teachers in High Education Institutions of MOE, China.
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2017, Journal of LuminescenceCitation Excerpt :It is reported that nanometer-sized particles can be grown into zero, one, two and three dimension through these synthesis methods. By far a large variety of α-Fe2O3 nanostructures have been synthesized, including the most common 0D spherical nanoparticles [16], 1D nanocrystals such as rod [19] wire [20] and tube [21], 2D layered structured such as Nano flakes [22], and complex 3D architectures such as dendrites and snowflakes [23], as well as hollow micro-spheres [24]. The aim of this work is to synthesize α-Fe2O3 nanoparticles using a cheaper sol-gel method and study the thermal annealing effect on their optical, structural and luminescence properties.