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Novel hexagonal WO3 (h-WO3) nanorods have been successfully prepared on a large scale by a simple hydrothermal method by adding Na2SO4. Uniform nanorods with diameters of 100–200 nm and lengths of up to several micrometres are obtained. The morphology evolvement and the growth mechanism were studied carefully with different quantities of Na2SO4. Different experimental parameters can lead to different structures and morphologies of the final products in our experiment. The current understanding of the growth mechanism of these nanostructures potentially provides important information about the structure design and morphology-controlled synthesis of WO3 and other oxides. The electrochemical performances of the as-prepared h-WO3 nanowires as anode materials of Li-ion batteries have also been investigated. These batteries have a discharge capacity of 215 mA h g−1 at the initial cycles and show an extreme capacity retention. The results imply that these h-WO3 nanorods are promising anode materials for Li-ion batteries.

The ultraviolet (UV) photoconductance properties of a single hexagonal WO 3 nanowire have been studied systematically. The conductance of WO 3 nanowires is very sensitive to ultraviolet B light and a field-effect transistor (FET) nanodevice incorporating a single WO 3 nanowire exhibits excellent sensitivity, reversibility, and wavelength selectivity. A high photoconductivity gain suggests that WO 3 nanowires can be used as the sensing element for UV photodetectors. Measurements under UV light in vacuum show that the adsorption and desorption of oxygen molecules on the surface of the WO 3 nanowire can significantly influence its photoelectrical properties. The WO 3 nanowires have potential applications in biological sensors, optoelectronic devices, optical memory, and other areas. KEYWORDSHexagonal WO 3 nanowire, ultraviolet, photodetector Since discovery of ultraviolet (UV) radiation, the applications of UV light in biotechnology, medical applications, astronomy, and materials science research have been an active research area [1]. In these activities, much attention has been paid to the issue of the safety of UV radiation. UV irradiation of human bodies can damage DNA structure, suppress the immune system, and increase skin photoaging, leading to an increasing number of cancer cases [2]. Therefore, highefficiency and low-energy consumption UV detectors are in high demand. Nano-photodetectors based on one-dimensional wide bandgap semiconductor materials in the form of nanowires, nanotubes, or nanofibers have been demonstrated to have very attractive performances due to the low dimensions and large surface-to-volume ratios of such nanomaterials [3][4][5][6]. To date, photoconductance based on wide bandgap semiconductors, for example, GaN, ZnO, Ga 2 O 3 , and Si 3 N 4 nanostructures, has been employed for UV detection [7][8][9][10].Tungsten oxide (WO 3 ), a very important type of semiconductor material, has been extensively investigated due to its promising physical and chemical properties [11][12][13][14]. By virtue of its outstanding electrochromic, optochromic, and gasochromic properties, in the past few decades WO 3 has been used to manufacture various devices such as flat-panel displays, electrochromic "smart" windows, optical modulation devices, write-read-erase optical devices, gas sensors, and field emission devices [15][16][17]. WO 3 is a potential material for detecting UV radiation because it has an indirect large energy band gap Nano Res (2010) 3: 281-287

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