Tungsten oxide nanowire may be prepared by hydrothermal method using Na2WO4•2H2O and HCl as raw materials with Na2SO4 as additive．
Hydrothermal Method to Prepare Tungsten Trioxide Nanowire
1. Weigh 3.68g (0.011mol) Na2WO4•2H2O into 20ml deionized water and stir it to dissolve;
2. Add 3M HCl to the above solution dropwise, stir it until the white precipitate no longer generated, and adjust the pH≈1;
3. Add in certain amount of 0.5M Na2SO4, continue to stir for 2h and transfer the solution to a 60ml PTFE-lined stainless steel reactor, sealed, placed in a constant temperature blast air oven, and reacted at 160°C for 12h;
4. Cool it down to room temperature, the obtained product by hydrothermal reaction was centrifuged and washed three times with deionized water and absolute ethanol respectively;
5. The washed product was transferred to a watch glass, then placed in a constant temperature air dry oven and dried at 100°C for 12 hours to obtain sample 1;
6. Change the concentration of additive while keeping the other conditions the same, i.e. replacing 0.5M Na2SO4 with 0.25M and 0.125M Na2SO4 to obtain Sample 2 and Sample 3 respectively.
The above samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), UV-Vis diffusion reflectance spectra (UV-vis), electron energy spectrum dispersion (EDS) and laser Raman spectroscopy (Raman) measurements．
The results show that the products via hydrothermal process are hexagonal WO3 nanowire with Na2SO4 as additive, and the thickness and length of nanowire have a slight difference, suggesting that different concentrations of Na2SO4 have certain influence on the grain size, but no effect on the crystal form and morphology．
Photocatalytic degradation of Rhodamine B solution (1×10-4mol/L) show that WO3 nanowire prepared in the presence of 0. 125M Na2SO4 has smallest size, the average diameter and length of the sample are respectively 5nm and 1um，exhibiting the best photocatalytic activity, and its degradation rate of Rhodamine B solution is 96. 01% under visible-light irradiation (≥420 nm) after 150 min．
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