A block copolymer solution was prepared by dissolving 0.2 g P123
in 5 ml anhydrous ethyl alcohol. A tungsten precursor of W(OC2H5)6
was slowly added into this solution to be 0.8 wt.%. Another ethanol
solution of 4.0 wt.% PVP was prepared in a separate bottle, and then
mixed with the W(OC2H5)6/P123 solution. This was magnetically
stirred for 12 h at room temperature to achieve a homogenous
composite solution. The composite solution was loaded into a 3 ml
plastic syringe with a metal needle at the tip. A high-voltage of 5.5 kV
was applied to the needle, and a grounded tube collector was placed
10 cm away from the needle tip. Composite WO3 nanofibers were
collected on a piece of aluminum foil at a steady flow rate of 0.4 ml/h.
Then, to form WO3 nanofibers, the as-electrospun nanofibers were
thermally treated at 120 °C overnight and then calcined at 500 °C in
air for 3 h. A slow heating rate of 2 °C/min was used to ensure the
formation of mesoporous WO3 nanofibers.