The sol-precipitation method, which is very useful for
obtaining pure, homogeneous, and nanosized powders,
was used to prepare precursor of the WO3 nanocrystallites.
WCl6 (Aldrich Co.) was dissolved in ethanol in a
N2 atmosphere and stirred at 70 ◦C for 48 h to obtain
a tungsten-alkoxide solution. The ammonia-hydroxide
solution was dropped into the mixed solution below pH
5.0 to precipitate the tungsten hydroxide. The precipitates
were washed with ethanol and dried at 100 ◦C.
WO3 fine powders were obtained after calcination in an
air atmosphere.