Controlled synthesis and gas-sensing properties of hollow sea urchin-like α-Fe2O3 nanostructures and α-Fe2O3 nanocubes
Introduction
Ammonia and various volatile organic compounds have been released in high quantities into the atmosphere as a result of human activities, and have generated environmental risks. Chemical sensors for the detection of these flammable and/or toxic gases play a very important role in chemical industries, environmental protection, public safety and human health. Metal oxides [1], [2], [3], [4], such as SnO2, ZnO, Fe2O3 and V2O5, function as gas-sensitive materials by changing their resistance due to exposure to oxidizing or reducing gases. Nevertheless, there are still some critical limitations to be overcome for the commercial sensors based on particulate or thin-film semiconductor metal oxides, such as limited maximum sensitivity, high working temperatures and lack of long-term stability [5]. Recently, nanorods, nanowires and nanoribbons of metal oxides were used to fabricate sensors; the results indicate that one-dimensional (1-D) nanomaterials are promising for highly sensitive chemical sensors [5]. Therefore, the fabrication of the metal oxide nanomaterials with a defined size and shape for gas sensor application is currently a major focus of nanoscience and nanotechnology.
Hematite (α-Fe2O3), the most stable iron oxide with n-type semiconducting properties (Eg = 2.1 eV) under ambient conditions, is widely used as catalysts, pigments, gas sensors, and electrode materials [3], owing to its low cost, high resistance to corrosion, and environmentally friendly properties. The previous studies mainly focused on the α-Fe2O3 films [6], [7], [8], [9], [10], [11] and powders [12], [13]. Stimulated by both the promising applications of iron oxides and the novel chemical and physical properties of nanoscale materials, considerable efforts have been made in the synthesis of α-Fe2O3 nanostructured materials with different morphologies. Up to now, a variety of α-Fe2O3 nanostructured materials in various geometrical morphologies have been successfully fabricated, such as nanoparticles [14], nanotubes [15], nanowires [16], nanobelts [16], nanocubes [17], nanorods [18], spindles [19], hollow spheres [20], [21], nanoplates [22], nanorings [23], rhombohedra [24] and complex hierarchical structures constructed with nanoscale building blocks [25], [26], [27], [28], [29], [30]. In particular, three-dimensional (3-D) superstructures assembled with one-dimensional nanorods have attracted much attention because of their unique properties and potential applications [28], [29], [30]. However, to our knowledge, the synthesis of hollow sea urchin-like α-Fe2O3 nanostructures has not been reported until now. The hollow nanostructures have widespread potential applications in catalysts, gas sensors, drug delivery, etc., owing to their higher specific surface area and lower density.
Recently, the nanorods [3], nanotubes [15], hollow spheres with a mesoporous shell [20], porous nanospheres [21], nanorings [23] and flutelike porous nanorods and hexapod-like nanostructures [31] of α-Fe2O3 have been used to fabricate gas sensors for the detection of ethanol, acetone, 92# gasoline, heptane, hydrogen, formaldehyde, toluene, acetic acid and ammonia. However, they did not investigate the stability of the sensors even though stability is one of the most important parameters of sensors. In addition, the sensing properties of hollow sea urchin-like α-Fe2O3 nanostructures and α-Fe2O3 nanocubes have not been studied until now.
In this paper, we report on controlled synthesis of hollow sea urchin-like α-Fe2O3 nanostructures and α-Fe2O3 nanocubes. Control over the both α-Fe2O3 nanostructures were achieved by adding different anions in the Fe3+–H2O hydrothermal system. To the best of our knowledge, this is the first report of the selective synthesis of α-Fe2O3 superstructures and nanocubes. The gas-sensing properties of the α-Fe2O3 superstructures, nanocubes and nanoparticle aggregations with irregular morphology in detecting ammonia, formaldehyde, triethylamine, acetone, ethanol and hydrogen were studied. The sensitivities of the as-prepared α-Fe2O3 superstructures are higher than that of nanocubes and nanoparticle aggregations of α-Fe2O3 with irregular morphology.
Section snippets
Synthesis
Hollow sea urchin-like α-Fe2O3 nanostructures: In a typical synthesis, 10 mL of 0.1 M sodium sulfate (Na2SO4) aqueous solution was added to 2 mL of 0.5 M iron chloride (FeCl3) solution under magnetic stirring. After stirring for 10 min, 8 mL of deionized water was added under constant stirring to form a homogeneous solution. The mixed solution was sealed into a Teflon-lined stainless steel autoclave of 50 mL capacity and heated at 140 °C for 12 h. After reaction, the autoclave was cooled to room
Microstructures of hollow sea urchin-like α-Fe2O3 nanostructures and α-Fe2O3 nanocubes
Fig. 2 shows the XRD patterns of the α-FeOOH precursors prepared by the hydrothermal reaction of FeCl3 with Na2SO4 at 140 °C for 12 h and α-Fe2O3 products obtained by calcining the precursors at 600 °C in air for 2 h. As can be seen in Fig. 2a, all the diffraction peaks of α-FeOOH precursors can be indexed to the pure orthorhombic α-FeOOH, which are consistent with the values in the literature (Joint Committee on Powder Diffraction Standards, JCPDS No: 81-0462). All the strong and sharp diffraction
Conclusions
In summary, hollow sea urchin-like α-Fe2O3 nanostructures have been successfully fabricated via the hydrothermal reaction of FeCl3 and Na2SO4 and subsequent annealing in air. Sensor based on the α-Fe2O3 superstructures shows high gas-sensing responses, short response and recovery time and long-term stability in detecting ammonia, formaldehyde, triethylamine, acetone and ethanol, indicating that these hollow sea urchin-like α-Fe2O3 nanostructures could be promising candidates as the building
Acknowledgments
This work was supported by National Natural Science Foundation of China (Grant No. 20573072) and Specialized Research Fund for the Doctoral Program of Higher Education (Grant No. 20060718010).
Fenghua Zhang was born 1982, and she is now a master student at the School of Chemistry and Materials Science under the supervision of prof. Heqing Yang. Her research project now focuses on “synthesis and characterization of α-Fe2O3 nanostructures”.
References (38)
- et al.
Nanopillar ZnO gas sensor for hydrogen and ethanol
Sens. Actuators B Chem.
(2007) - et al.
Preparation and gas sensing properties of vanadium oxide nanobelts coated with semiconductor oxides
Sens. Actuators B Chem.
(2006) - et al.
Characterization and gas-sensing properties of nanocrystalline iron (III) oxide films prepared by ultrasonic spray pyrolysis on silicon
Sens. Actuators B Chem.
(2000) - et al.
Fabrication and gas sensing properties of α-Fe2O3 thin film prepared by plasma enhanced chemical vapor deposition (PECVD)
Sens. Actuators B Chem.
(2001) - et al.
Sol–gel route to pseudocubic shaped α-Fe2O3 alcohol sensor: preparation and characterization
Sens. Actuators B Chem.
(2005) - et al.
The influence of morphology on the response sensors of iron-oxide gas sensors
Sens. Actuators B Chem.
(1995) - et al.
NO2 gas sensitivity of sol–gel-derived α-Fe2O3 thin films
Thin Solid Films
(1995) - et al.
Characterization and gas-sensing behavior of an iron oxide thin film prepared by atomic layer deposition
Thin Solid Films
(2008) - et al.
Preparation and characterization of nanocrystalline α-Fe2O3 by a sol–gel process
Sens. Actuators B Chem.
(1997) - et al.
Structural and gas sensing properties of ultrafine Fe2O3 prepared by plasma enhanced chemical vapor deposition
Mater. Sci. Eng. B
(1997)
Fractal growth of single-crystal α-Fe2O3: from dendritic micro-pines to hexagonal micro-snowflakes
Mater. Lett.
Synthesis of hollow microspheres constructed with α-Fe2O3 nanorods and their photocatalytic and magnetic properties
J. Alloys Compd.
Preparation and gas-sensing properties of thermally stable mesoporous SnO2
Sens. Actuators B Chem.
Facile synthesis of SnO2 hollow nanospheres and applications in gas sensors and electrocatalysts
Eur. J. Inorg. Chem.
Synthesis of hematite (α-Fe2O3) nanorods: diameter-size and shape effects on their applications in magnetism, lithium ion battery, and gas sensors
J. Phys. Chem. B
Hydrothermal synthesis and gas sensing characters of ZnO nanorods
Sens. Actuators B Chem.
Easy synthesis and magnetic properties of iron oxide nanoparticles
Chem. Mater.
α-Fe2O3 nanotubes in gas sensor and lithium-ion battery applications
Adv. Mater.
Controlled growth of large-area, uniform, vertically aligned arrays of α-Fe2O3 nanobelts and nanowires
J. Phys. Chem. B
Cited by (0)
Fenghua Zhang was born 1982, and she is now a master student at the School of Chemistry and Materials Science under the supervision of prof. Heqing Yang. Her research project now focuses on “synthesis and characterization of α-Fe2O3 nanostructures”.
Heqing Yang received his PhD degree from Xi’an Jiaotong University in 1999. He did his post-doctorial research in Fudan University for two years from 2000 to 2002. Now, he is doing research in the School of Chemistry and Materials Science, Shaanxi Normal University. He is currently involved in research on using nanostructured materials as gas sensors, catalysts and biosensors.
Xiaoli Xie received her MS degree in physical chemistry in 2008 from Shaanxi Normal University, Xi’an, China.
Li Li received her MS degree in inorganic chemistry in 2002 from Northwest University, China. She is now a PhD student at the School of Chemistry and Materials Science under the supervision of prof. Heqing Yang.
Lihui Zhang received her MS degree from the School of Chemistry and Materials Science, Shaanxi Normal University, in 2004. She is now a PhD student at the School of Chemistry and Materials Science under the supervision of prof. Heqing Yang.
Jie Yu was born in 1982, and he is now a master student at the School of Chemistry and Materials Science under the supervision of prof. Heqing Yang.
Hua Zhao was born in 1982, and he is now a master student at the School of Chemistry and Materials Science under the supervision of prof. Heqing Yang.
Bin Liu received his MS degree from the School of Chemistry and Materials Science, Shaanxi Normal University, in 2004. He is now a PhD student at the School of Chemistry and Materials Science under the supervision of prof. Heqing Yang.