Fabrication of α-Fe2O3@graphene nanostructures for enhanced gas-sensing property to ethanol
Introduction
Over the past few years, hematite (α-Fe2O3) has attracted much attention in different fields owing to its many excellent properties such as low cost, environment-friendly, multiple functions, corrosion resistance under ambient conditions and high stability [1], [2], [3]. It has been widely studied for applications in magnetic devices, catalysts, water treatment, pigments, lithium batteries, sensors, photocatalyst, biological and medical fields [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19].
As an important gas sensor material, α-Fe2O3 is a n-type semiconductor (Eg = 2.1 eV), whose performance strongly depends on the morphology, specific surface area and structure. Recently, Wang et al. reported on the synthesis of three-dimensional hierarchical flowerlike α-Fe2O3 nanostructures via a simple solvothermal method, and the product presents excellent ethanol sensing performances, quick response and recovery times because of the unique porous and well-aligned nanostructures [20]. Sun et al. prepared mesoporous α-Fe2O3 nanostructures by the soft template synthesis method, presenting better gas sensing performance toward acetic acid and ethanol gas than its nanosphere and nanowire counterparts [21]. Based on these results, the kind of loose-hierarchical structures of α-Fe2O3 materials are considered as good candidates for gas sensors because they have larger surface-area-to-volume ratio and lower density than solid structures. However, the improvement on the detection sensitivity and stability still remains to be further improved and perfected. Therefore, the seeking and development of effective strategy to synthesize various kinds of loose-hierarchical structure materials with improved gas sensing properties are highly desirable.
As a new carbon material, graphene possesses a special two-dimensional (2D) crystalline structure, remarkable electrical and thermal conductivity, larger surface-area-to-volume ratio, high chemical stability and excellent adsorptivity [22], [23], [24], [25], [26], [27], [28], [29], [30], [31]. Therefore, graphene is a good precursor for producing this kind of loose-hierarchical structure materials. An et al. have shown that the synthesized WO3 nanorods/graphene nanocomposites behave high-efficiency visible-light-driven photocatalysis and NO2 gas sensing [32]. Neri et al. investigated the sensing behavior of SnO2/reduced graphene oxide nanocomposites toward NO2 [33]. Moreover, Esfandiar explored the decoration of TiO2/reduced graphene oxide with metal nanoparticles, exhibiting wide range of hydrogen sensitivity, low working temperature and fast response time [34]. Actually, there are lots kind of metal oxides (ZnO [35], [36], [37], TiO2 [38], [39], Fe3O4 [40], [41], [42], SnO2 [43], MnO2 [44], [45], [46] and Co3O4 [47]) have been reported to constitute composite materials with graphene in order to improve their performances. However, to the best of our knowledge, few studies on the gas-sensing properties of Fe2O3-graphene nanocomposites have been reported so far.
Herein, we develop a one-step facile hydrothermal route to directly fabricate α-Fe2O3@graphene nanocomposites with different graphene contents. The as-prepared products exhibit good gas-sensing performance to ethanol in comparison with pure α-Fe2O3. It is important to note that the graphene content in nanocomposites plays a great role on the gas sensor performance, and the Fe2O3@graphene nanocomposite contained 2% graphene by mass gives the best activity. Moreover, a comparative gas sensing study between the as-synthesized α-Fe2O3@graphene and pure α-Fe2O3 was performed to demonstrate the reason for improving gas sensitive performance of obtained nanocomposites.
Section snippets
Synthesis of α-Fe2O3@graphene composites
Graphene oxide (GO) was synthesized from purified natural graphite bought from Qingdao Zhongtian Company with a mean particle size of 44 μm according to Hummers method [48]. All the other chemical reagents used in this experiment were of analytical grade (Shanghai Chemical Reagent Company). The α-Fe2O3@graphene nanocomposite with differing graphene contents (1,2,3,4,5 wt%, calculated by the feeding ratio of GO) were synthesized. A typical experiment for the synthesis of α-Fe2O3@graphene
Structure and morphology of α-Fe2O3@graphene nanocomposites
The XRD diffraction patterns of the as-prepared pure Fe2O3, Fe2O3-G (0.02) and Fe2O3-G (0.05) are shown in Fig. 2. The diffraction peaks in these samples are assigned to α-Fe2O3 (JCPDS 79-1741), and no other phase is observed in the patterns [52]. It is interesting to note that the α-Fe2O3@graphene composites present more obvious diffraction peaks than those of pure Fe2O3, implying that the presence of graphene facilitates the crystallization of Fe2O3. However, no typical diffraction peaks of
Conclusions
In summary, α-Fe2O3@graphene nanocomposites gas-sensing material with different graphene contents has been successfully prepared via a one-step hydrothermal method. The graphene sheets are decorated with Fe2O3 nanoparticles with average diameters of 80 nm. The sensor based on Fe2O3-G (0.02) exhibits the best performance in all sensors investigated in this work when operating at 280 °C. The response value of 1–1000 ppm ethanol is much higher than that of pure Fe2O3 counterpart in the same
Acknowledgments
This investigation was supported by the Jiangsu Funds for Distinguished Young Scientists (BK2012035), Program for New Century Excellent Talents in University (NCET-11-0834), the Natural Science Foundation of China (No. 51322212, 21206075), the Fundamental Research Funds for the Central Universities (No. 30920130111004, 2012ZDJH002).
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