A high performance hydrogen sulfide gas sensor based on porous α-Fe2O3 operates at room-temperature
Introduction
Hydrogen sulfide (H2S), as a commonly-used chemical gas is extensively utilized in metallurgy, medicine, pesticide and catalyst fields. However, H2S also is an inflammable and malodorous toxic gas, which is harmful to the human nerve and respiratory system even at low concentration. As generally reported, the short term (10 min) and long term (8 h) exposure limit of H2S has been set to 15 ppm and 10 ppm, respectively. When the concentration reaches over 15 ppm, the human olfactory nerve would be paralyzed and the ability to sense H2S declines [1], [2], which could result in lethal consequences. Hence, it is urgent to develop a high-performance H2S gas sensor with high-efficiency, high-reliability, high sensitivity, low cost, low detection limits, and low operation temperature for environmental protection and personal safety during industrial production process.
In recent years, numerous materials including metal oxide semiconductor materials, such as In2O3 [3], [4], WO3 [5], [6], ZnO [7], [8], [9], SnO2 [10], and novel functional materials, such as graphene [11], carbon nanotube [12] have been exploited as H2S gas sensor due to their superior sensing performance towards H2S gas. Among them, the metal oxide semiconductor (MOS) based gas sensors have gained special focus because of their low manufacturing cost, low operation power consumption, simple design, and ease of incorporation into microelectronic devices with possible high device integration density. Of various metal oxide based H2S gas sensors, the α-Fe2O3 based sensors have been proven to be promising due to their high sensitivity, high selectivity and non-toxicity.
Hematite (α-Fe2O3), which is the most stable iron oxide, possesses n-type semiconducting properties with a band gap of 2.1 eV under ambient conditions [13]. As an important and promising functional material, α-Fe2O3 has been widely applied in various areas including photo-catalyst, magnetic materials, waste-water treatment, anode material of lithium batteries [14], [15], [16], [17], [18]. Additionally, it is considered as a good candidate in the gas sensing field. It is well known that the gas sensing properties of α-Fe2O3 dependent strongly on its morphologies, such as aspect ratio, size, orientation and crystal density [19]. Thus, over the past decades, considerable efforts have been made to improve the sensor's sensitivity and selectivity, stability and reproducibility by controllable synthesis of various α-Fe2O3 nanostructures, such as nanospindles [20], nanorings [21], nanospheres [22], nanorods [23], nanowires [24] etc., Moreover, α-Fe2O3 with porous structure has been demonstrated to be an favorable architecture for boosting gas sensing performance due to the porous structures’ significantly enhanced the surface-area-to-volume ratio and material's active sites, which would make the gas diffusion or mass transport onto the surface of materials much more convenient and effective in comparison to the solid ones [25], [26], [27]. For example, Wang et al. synthesized porous α-Fe2O3 nanorods by a facile solution approach, and then utilized the material as a gas sensor for ethanol detection [23]. Deng et al. reported a high-performance H2S gas sensor based on porous α-Fe2O3 nanospheres by microwave-assisted a hydrothermal process [28]. However, it is a disadvantage that most porous α-Fe2O3 based gas sensors reported previously operate at high temperature (200–500 °C), which severely restricted its practical application. Therefore, reducing working temperature or operating at room-temperature would be of great significance.
Hence, in this paper, we report a high-performance room-temperature H2S gas sensor based on porous α-Fe2O3, prepared by the annealing of β-FeOOH precursor derived from a facile hydrothermal method. The sensing characteristics including sensitivity, selectivity, stability, response time and recovery time are investigated. In addition, the H2S sensing mechanism of porous α-Fe2O3 based sensors is also discussed.
Section snippets
Experimental procedure
All the reagents were of analytical grade and used without any further purification, purchased from Sinopharm Chemical Reagents Co., Ltd. (Shanghai, china). Besides, all the water used throughout the experiment was deionized water with a resistivity of 18.3 MΩ cm.
The preparation of the porous α-Fe2O3 nanoparticles consists of two steps including the formation of β-FeOOH precursor prepared by hydrothermal reaction and the further annealing of the as-prepared β-FeOOH precursor. In a typical
Structural and morphology characterization
Fig. 3 shows the XRD patterns of the obtained precursor and the final product by annealing the precursor at 500 °C for 2 h. As is shown in Fig. 3a, all of the diffraction peaks correspond well to the tetragonal β-FeOOH (JCPDS NO.34-1266) and no impurities peaks can be observed in the patterns, indicates the high purity of the product. Fig. 3b displays the XRD pattern of the final product. It can be seen that all the diffraction peaks are well matched with the standard hexagonal structure of
Conclusions
In summary, a novel porous α-Fe2O3 nanoparticles based gas sensor was reported in this work. The fabrication process involves the formation of β-FeOOH as a precursor and thermal conversion β-FeOOH to porous α-Fe2O3 by annealing treatment. As a gas sensor, it showed a high-performance in H2S detection, the response to 100 ppm H2S gas reached 38.4 at room temperature and the detection limit was as low as 50 ppb. Moreover, the sensor also exhibited an excellent selectivity, reproducibility and
Acknowledgments
This work was supported by the Fundamental Research Funds for the Central Universities (ZYGX2012J047), the Joint Fund of the National Natural Science Foundation of China and the China Academy of Engineering Physics (U1330108).
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