Hexagonal WO 3 (hex-WO 3 ) nanowires with high aspect ratio and crystallinity have been prepared for the first time by a microwave-assisted hydrothermal method. By using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and high resolution transmission electron microscopy, the phase and morphology of the products were identified, which were controlled by reaction temperature, holding time and added salts. Uniform hex-WO 3 nanowires with a diameter of 5-10 nm and lengths of up to several micrometres were synthesized by a microwave-assisted hydrothermal process at 150 C for 3 h in a solution containing (NH 4 ) 2 SO 4 as a capping reagent and Na 2 WO 4 as a starting material. The aspect ratio and specific surface area of hex-WO 3 nanowires were 625 and 139 m 2 g À1 , respectively, which represented one of the highest values reported for WO 3 . The electrocatalytic activity for hydrogen evolution reaction of hex-WO 3 nanowires was also investigated by cyclic voltammetry and linear sweep voltammetry. The results demonstrated that hex-WO 3 nanowires were a promising electrocatalyst for the hydrogen evolution reaction (HER) from water. Experimental Synthesis and characterizationTo synthesize 1D WO 3 , 2 g analytical grade sodium tungstate dihydrate (Na 2 WO 4 $2H 2 O) were dissolved in 45 ml distilled water under stirring at room temperature and 5 ml 3 M HCl was

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In this research, the effects of pH, reaction temperature and holding reaction time on the synthesis of one-dimensional ZnWO 4 nanostructures by a hydrothermal method were studied. Phase, morphology and atomic vibration were characterized by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and Fourier transform infrared (FTIR) and Raman spectroscopy. The pure monoclinic ZnWO 4 structure was synthesized at the pH solutions of 7 and 8. By varying the pH values, the mixtures of monoclinic ZnWO 4 and hexagonal ZnO as major and minor phases were detected at the pH 9 and 10 solutions, and the pure hexagonal ZnO phase at the pH 11 and 12. SEM and TEM images proved that ZnWO 4 nanorods grew along the [021] direction, with the reaction temperature and time to control their morphologies. The Zn-O, Zn-O-W, and W-O stretching vibrations were detected at 474, 888, and 726 cm À1 , and their corresponding bending vibrations at 430, 826, and 582 cm À1 , respectively. The optical properties of ZnWO 4 nanorods were also investigated by UV-visible (UV-vis) and photoluminescence (PL) spectroscopy. The above analyses proved that the appropriate condition for synthesizing of ZnWO 4 nanorods is at pH 8 by the 200 C and 24 h hydrothermal treatment.

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