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 for 12 h. After that, the autoclave was allowed to
cool down naturally. The finally products were collected and
washed with deionized water and ethanol several times and
dried in air at 80 °C. The WO3 nanowires were finally obtained.