Synthesis of α-Fe2O3 with the aid of graphene and its gas-sensing property to ethanol
Introduction
Over the past few years, hematite (α-Fe2O3) has attracted a great deal of attention in different fields because of its low cost, nontoxicity, environment-friendly, corrosion resistance under ambient conditions, high stability and multiple functions [1], [2]. It has been intensively investigated for applications in water treatment, magnetic devices, pigments, catalysts, sensors and medical fields [3], [4], [5], [6], [7], [8], [9], [10]. Consequently, great efforts have been devoted to the synthesis of α-Fe2O3 nanoparticles with different morphologies owing to its novel chemical and physical properties.
Especially, the key issue for Fe2O3 preparation is to control their aggregation to get well-dispersed nanoparticles, which is significant for improving their gas-sensing properties. Recently, Zhang and co-workers reported the synthesis of hollow sea urchin-like α-Fe2O3 nanostructures and nanocubes via a hydrothermal and annealing method, and the products show high gas-sensing responses, short response/recovery time and long-term stability in detecting many organic gases including ethanol [11]. Sun et al. prepared bundle-like α-Fe2O3 nanorods by a simple calcination of β-FeOOH precursor derived from a hydrothermal method in the presence of vinyl pyrrolidone, presenting good gas sensing performance toward acetone and ethanol [12]. Li et al. showed that the single-crystalline α-Fe2O3 has high sensitivity, short recovery time and good reproducibility toward ethanol and acetone [13]. Moreover, Song et al. developed a simple hydrolysis method for synthesizing large-scale α-Fe2O3 hollow microspheres, exhibiting a potential application in ethanol detection [14]. Up to now, α-Fe2O3 nanoparticles with various morphologies, such as nanobelts, microspheres, hollow spindles, quasicubes, nanowires, rhombohedra and nanorings, have been fabricated [15], [16], [17], [18], [19], [20], [21]. Based on these results, the α-Fe2O3 with high dispersion and controllable shape are considered as appropriate candidates for gas sensors. Therefore, the development of an effective method to synthesize well-dispersed α-Fe2O3 with high gas sensing property is highly desirable.
Herein, we developed a two-step route to fabricate α-Fe2O3 nanoparticles via a hydrothermal reaction between Fe(NO3)3 and CH3COONa, and subsequent annealing in air at 600 °C for 1 h. The as-prepared product exhibits excellent gas-sensing performance to ethanol. It is important to note that the graphene content in precursor of α-Fe2O3 plays a great role on gas sensing performance of obtained α-Fe2O3. Moreover, a comparative gas sensing study between as-synthesized α-Fe2O3 in the presence of graphene and pure α-Fe2O3 was performed to demonstrate the reason for improving gas sensitive performance of obtained nanoparticles.
Section snippets
Preparation of graphene oxide (GO)
GO was synthesized from purified natural graphite (bought from Qingdao Zhongtian Company) with a mean particle size of 44 μm according to Hummers and Offerman method [22]. All the other chemicals were of analytical grade and used without further purification.
Synthesis of α-Fe2O3@graphene nanocomposites
The α-Fe2O3@graphene nanocomposites with differing graphene contents (5, 10, 20, 30, 40 and 50 wt%, calculated by the feeding ratio of GO) were synthesized by a hydrothermal reaction. A typical experiment for synthesis of α-Fe2O3@graphene
Structure and morphology of as-prepared nanoparticles
XRD diffraction patterns of the as-prepared pure Fe2O3&H, Fe2O3–G (0.2) and Fe2O3–G (0.2)&H are shown in Fig. 2. The diffraction peaks in these samples are assigned to α-Fe2O3 (JCPDS 33-0664) [11]. The peaks at 2θ value of 24.1, 33.2, 35.6, 40.9, 49.5, 54.1, 62.4 and 64.0o can be indexed to (012), (104), (110), (113), (024), (116), (214) and (300) crystal planes of α-Fe2O3, respectively. However, no typical diffraction peaks of GO or graphene are observed in the XRD pattern of Fe2O3–G (0.2).
Conclusions
In summary, Fe2O3–G (0.2)&H nanoparticles have been successfully prepared via a two-step method. The addition of graphene can effectively improve the dispersion of Fe2O3 nanoparticles. The sensor based on Fe2O3–G(0.2)&H exhibits high sensor performance at 280 °C, and the response value of 19–1000 ppm of ethanol is much higher than that of pure Fe2O3 counterpart in the same conditions. Importantly, it is found that the addition of graphene plays an important role for improving the dispersion of Fe2
Acknowledgment
This investigation was supported by the Jiangsu Funds for Distinguished Young Scientists (BK2012035), the National Natural Science Foundation of China (Nos. 51322212, 21206075), the Research Fund for the Doctoral Program of Higher Education of China (No. 20093219120011), and the National Basic Research Program of China (2014CB931700/2014CB931702).
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