Low-heating solid-state synthesis and excellent gas-sensing properties of α-Fe2O3 nanoparticles
Introduction
Semiconductor metal oxides have received considerable attention because of their novel properties and versatile technological applications in past years [1], [2], [3]. Hematite (α-Fe2O3), the most stable iron oxide, with n-type semiconducting properties under ambient conditions, has been investigated as gas sensor, rechargeable lithium-ion batteries and catalyst owing to its low cost, good reversibility and long-term stability [4], [5]. Recently, Fe2O3 nanomaterials show better properties for the detection of reducing gas at the lower working temperature than SnO2 and ZnO [6], [7], [8], [9], [10]. Several techniques including of template methods, solvothermal methods, chemical vapor deposition, sol–gel synthesis and electrospinning fabrication have been used to fabricate α-Fe2O3 nanomaterials [10], [11], [12], [13], [14], [15]. But it still remains a challenge to develop simpler method to controlled fabricate α-Fe2O3 nanomaterials.
Solid-state synthesis has the advantage of simple process, high yield and low cost. Especially, there is no limit of reactant solubility in the design of chemical reaction system unlike in the liquid phase system. But high temperature is usually required for traditional solid-state synthesis, which result in the high energy consumption and long time-consuming. Low-heating solid-state synthesis that was applied at low temperature less than 100 °C has been studied and developed to synthesize the inorganic nanomaterials in recent years [16], [17], [18], [19], [20], [21]. This method has attracted more and more attention due to the simple process, low energy consumption and mild condition.
In this paper, α-Fe2O3 nanoparticles with different size were synthesized by the speed-controlled solid-state chemical reaction. To the best of our knowledge, there is little report about synthesizing size-different ferric oxide by the control of reaction speed in solid-state chemical reaction. The gas-sensing properties of α-Fe2O3 to the different gas were systematically investigated. The influence of size on gas-sensing properties of α-Fe2O3 was discussed.
Section snippets
Synthesis
All the regents are analytical pure and were used without further purification. In a typical synthesis, 2.78 g (10 mmol) of FeSO4·7H2O and 2.10 g (35 mmol) urea were mixed and ground for 50 min at room temperature, the caesious paste was formed, and heated at 50 °C in water bath for 1 h. Then the product was calcined at 400 °C for 2 h in air, and washed with distilled water and ethanol for removing the excrescent salt and dried in air. Another product was fabricated followed the same procedure using
The microstructure of the products
Fig. 1 shows the XRD patterns of the products prepared by the solid-state reaction technique. It can be seen that all of the diffraction peaks could be indexed to α-Fe2O3 (JCPDS No. 33-0664). No characteristic peaks were observed for other impurities such as ferroferric oxide or ferrous iron oxide. The average crystallite size (D) was determined from the X-ray line broadening using Scherrer's formula, D = 0.89 λ/β cos θ, where λ is the wavelength (Cu-Kα1), β is the full width at the half maximum
Conclusions
In summary, α-Fe2O3 nanoparticles have been controlled synthesized by low-heating solid-state reaction. The products with smaller size can be obtained through slowing down the reaction speed of solid-state reaction. The α-Fe2O3 nanoparticles have high response value to ethanol and acetone, fast response/recovery characteristic and good long-time stability at lower working temperature than commercial materials, which can be regarded as excellent potential candidates for ethanol and acetone
Acknowledgements
This work was financially supported by the Natural Science Foundation of Xinjiang University (BS100129 and XJEDU2012I03), the Natural Science Foundation of Xinjiang Province (No. 2010211A09), the National Natural Science Foundation of China (Nos. 21101132, 21061013 and 21271151), Xinjiang Autonomous Region with Science and Technology Project Plan (No. 200991101), Autonomous Regions High Technology Research and Development Program (No. 201016118) and Program for Changjiang Scholars and
Yali Cao is an associate professor at Institute of Applied Chemistry, Xinjiang University of China. She received her PhD in Materials science and Engineering from Xi’an Jiaotong University of China in 2009. Her current research interests are in the area of metal oxide semiconductor gas sensor and nanostructured materials.
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Yali Cao is an associate professor at Institute of Applied Chemistry, Xinjiang University of China. She received her PhD in Materials science and Engineering from Xi’an Jiaotong University of China in 2009. Her current research interests are in the area of metal oxide semiconductor gas sensor and nanostructured materials.
Haiyang Luo is a master student at Institute of Applied Chemistry, Xinjiang University of China. Her current research work is concentrated on the synthesis for nanometer functional materials by solid-state reaction technique.
Dianzeng Jia is a professor at Institute of Applied Chemistry, Xinjiang University of China. His research field is the studies on nanometer functional materials and photochromic materials.