Large-scale hydrothermal synthesis of WO3 nanowires in the presence of K2SO4
Introduction
Over the past few years, much effort has been devoted to the synthesis of semiconductor nanowires, nanorods, and nanobelts, because of the importance of understanding the dimensionality confined transport phenomena and fabricating nanodevices and nanosensors [1], [2], [3], [4]. Many attempts have been made to synthesize one-dimensional nanostructured materials [5], [6], [7], [8], [9], [10], [11], [12], [13], [14]. Of the methods used in 1D nanostructure synthesis, hydrothermal processes have emerged as powerful tools for the fabrication of anisotropic nanomaterials with some significant advantages, such as controllable particle size and low-temperature, cost-effective, and less-complicated techniques. Under hydrothermal conditions, many starting materials can undergo quite unexpected reactions, which are often accompanied by the formation of nanoscopic morphologies that are not accessible by classical routes.
Among various metal oxides, WO3 is a versatile wide band-gap semiconductor for many valuable applications. WO3 has found useful applications in semiconductor gas devices [15], electrochromic devices [16], and photocatalyses [17]. Thus far, preparation of single-crystalline, 1D nanostructured tungsten oxide in mass quantity has been accomplished by heating a tungsten foil, covered by SiO2 plate, in an argon atmosphere at 1600 °C [18] or recently by electrochemically etching a tungsten tip, followed by heating at 700 °C under argon [19]. The employed harsh conditions, contamination by platelets, and uncontrolled size hamper systematic investigations on size-dependent properties of 1D nanostructured tungsten oxide itself as well as of inorganic derivatives prepared from the oxide. Recently, the hydrothermal synthesis of ultralong and single-crystalline Cd(OH)2 nanowires using alkali salts as mineralizers was reported by Tang et al. [20]. The 1D nanostructure synthesis using inorganic salt instead of surfactant and water-soluble high molecule has strong points in non-pollution, low-cost, easy-cleanout and recovery. Herein, we describe a facile inorganic route for synthesis of uniform WO3 nanowires in aqueous solution. This novel method is based on treating freshly prepared H2WO4 in the presence of K2SO4 salt under hydrothermal conditions at 180 °C for 12 h.
Section snippets
Synthesis of WO3
Na2WO4 (1 g) was dissolved in 30 ml deionized water to form a transparent solution. A (3 mol l− 1) HCl solution was added dropwise into the above solution under continuous stirring until tungstenic acid was precipitated thoroughly. Next, the centrifuged precipitate was dissolved in 30 ml deionized water, 40 g K2SO4 was added to the system and agitated to form starchiness, and then transferred into Teflon-lined autoclave with a capacity of 50 ml. Hydrothermal treatments were carried out at 180 °C
Results and discussion
The morphologies of the final products were demonstrated in Fig. 1a–c. On the basis of the SEM check, the proportion of the nanowire morphology was estimated to be about 100% (Fig. 1a). As shown in the SEM images, the average diameter of these uniform nanowires was about 10 nm and the length was up to several microns (Fig. 1b). Therefore, the nanowires reached a high aspect ratio of more than 500. A TEM image of a single nanowire with diameter of about 10 nm was shown in Fig. 1c. The selected
Conclusion
In summary, tungsten oxide nanowires with relatively uniform diameters ranging from 10 to 20 nm and lengths up to several micrometers were synthesized on a large scale. With the distinctive and promising properties of tungsten oxide, the as-synthesized nanowires may serve as functional materials in the fabrication of nanosized sensors and flat panel display systems. The important role of K2SO4 salt in the synthesis has been demonstrated. This aqueous route should be feasible for large-scale
Acknowledgment
We wish to acknowledge the financial support from the Natural Science Foundation of Fujian Province (no: 2006J0153).
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